DERMATOLOGICAL LASER AND AESTHETIC LASER

TREATMENTRS: AN OVER VIEW

AFSANEH JAVANMARD

1. Introduction

The ability to control and use optical energy, especially in the form of laser, is one of the most

significant achievements of science in the 20th century. Very few inventions or developments in any

field of science, has ever produced such a dramatic impact as laser.

Laser, is a very focused and narrow beam of light. Nevertheless, it is not just an ordinary light. It is a

special type of light with unique characteristics and important properties.

As the result of these special qualities and our ability to radiate it in a controlled manner, laser can be

used to perform a very wide range of different tasks.

Some article on the en.wikipedia.org even remarks that when laser was first made back in 1960, it was

even called “a solution looking for a problem”! This has been proved right. Nowadays, laser has

become ubiquitous and is an essential and inseparable tool for us. It is being utilised in thousands of

highly varied applications to perform a whole range of various tasks.

Laser applications are now vastly and commonly used and relied on in every section of our modern

society, including consumer electronics, telecommunications, industry, construction, science,

medicine, dentistry, education, law enforcement, police force, as well as military fields. Its

applications are constantly expanding in a very high speed (schools-wikipedia.org/wp/l/laser.htm,

2008/9).

Information materials on the www.cut-tec.co.uk suggest that industrial lasers are used for welding,

material heat treatment, making parts, cutting trough very heavy metals at an unmatchable speed,

drilling very accurately through hard and brittle materials, and operating many other precise

machinery works.

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Finely controlled and highly accurate lasers are widely used in medicine. Medical lasers can perform

very precise and delicate tasks, in a broad range of remedial, surgical and clinical, diagnostic

procedures. examples include bloodless surgery, laser tissue welding, vaporising tissues, coagulating

large blood vessels, cutting and volume ablation of tissues, laser scanning cytometry, low-level laser

therapy, ablating tumours, kidney stone treatments, photo bio-stimulation, laser wound healing,

ophthalmic surgery, scar revision, tattoo ablation and hair removal (emedicine, 2008).

Scientists use laser in great extends to carry out wide spectrums of different studies, researches,

experiments, and new breakthroughs, in all different areas of science; which would have been

impossible to achieve without utilising laser. www.wikipeia.org/wiki/laser lists different usages for

laser in science and suggests that scientists use laser to explore and study molecular, atomic and sub-

atomic structures, to measure ultra small atomic and sub-atomic or mega large astronomic lengths,

volumes and sizes, to calculate very high speeds, and even to detect tiny amounts of matters in space

with an incredible accuracy. It also suggests that laser has many other scientific uses for example

spectroscopy, laser annealing, laser inerfermometry and LIDAR.

In military section, laser is widely used to assist with many different tasks like marking targets,

guiding munitions, missile defence, electro-optical countermeasures (EOCM) and as RADAR

alternative (school-wikipedia.org, 2008/9).

Different laser equipped devices and consumer products are now very common features in our homes,

offices, shops, schools, and universities. The supermarket barcodes, CD and DVD players, computers

and laptops, scanners, pointing pens, printers and many more applications, all utilise different types of

laser (physic2000.com, 2008).

The list goes on. In fact, school-Wikipedia (2008/9) estimates that in the year 2004, excluding diode

lasers, approximately 131,000 units of different types of laser machines were sold worldwide,

Worthing a value of US$2.19 billion. In the same year, approximately 733 million units of diode laser

machines, with a value of US$3-20 billion, were sold!

1.1 History of laser

It is well acknowledged by all physic scientists and researchers that Albert Einstein laid the

groundwork for the invention of the laser in 1916, and developed the theoretic principles behind laser

and its predecessor, the maser (schools-wikipedia.org/wp/l/laser.htm, 2008).

As Silfvast (1996) explains in his book, Einstein’s treatise called “ON the Quantum Theory of

Radiation” was a groundbreaking re-derivation of Max Planks’ law of radiation based on the concept

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of probability coefficients for the absorption, spontaneous and stimulated emission and won him the

Nobel Prize. This concept was later termed “Einstein coefficients’” and was the first step toward

discovery of laser phenomenon.

Following that, Valentin A. Fabrikant, in 1939, suggested the possibility of amplifying short

electromagnetic waves by using the stimulated emission (en.wikipedia.org/wiki/laser, 2008).

In 1947, Willis Lamb and R.C. Retherford found apparent stimulated emission in hydrogen spectra

and succeed to demonstrate the stimulated emission for the first time (en.wikipedia.org/wiki/laser,

2008).

In 1950, a physic scientist called Alfred Kastler suggested the idea of using optical source of energy

to excite a material and induce emission. Two years later, he and his colleagues Brossel and Winter,

managed to experiment their suggested methods successfully for the first time, and confirmed their

theory(school-wikipedia.org/wp/l/laser, 2008/9).

Charles H. Townes and one of his graduate students called James P. Gordon produced the first maser,

the predecessor of laser, in 1953. Maser was a device that was developed on the principle of

stimulated emission, but amplified radiation in the microwave length region of electromagnetic

spectrum rather than infrared or visible light (Fox, 2008).

Townes later said, while working on the development of maser, he had encountered many oppositions

from some of his eminent scientist colleagues who thought the idea of maser was theoretically and

practically impossible (Physiol Rev., 1955 cited in Lee, 2008).

However, the maser device Townes developed, was incapable of maintaining a continuous radiation

output. Two other scientists from Soviet Union called Nikolay Basov and Alexandra Prokhporov,

worked independently on the developing a quantum oscillator and succeed to solve the problem of

maintaining a continues radiation output, by using more than two quantum energy level. The device

they developed used an optical pumping and was a multilevel system. In this system between the

ground state and upper energy level, there is a meta-stable energy level where atoms or molecules

remain for slightly longer than the upper energy level, before falling back to the ground state. When

atoms or molecules get excited to the high and unstable energy level, then fall into the meta stable

level rapidly enough, they would accumulate in that meta stable energy level and would build up the

population inversion. Therefore, the system could maintain the radiation output (en.wikipedia.org,

2008).

Townes, Basov, and prokhorov shared the 1964 Nobel Prize in physic “for fundamental work in the

field of quantum electronic, which has led to the construction of oscillators and amplifiers based on

maser-laser principle” (school-wikipedia.org, 2008).

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In 1957, Charles Townes and his scientist colleague called Arthur Leonard Schawlow, at Bell

laboratories, proposed the idea of inducing emission and amplifying radiation in the visible light

wavelength. They called the concept an “optical maser.” They developed the physical operating

principles for the optical maser a year later. Schawlow and Townes sent a manuscript of their

suggested operating principles and their theoretical calculation to Physical Review, which published

their paper that year (Volume 112, Issue 6) (Schawlow & Townes, 1958 cited in Lee, 2008).

Around the same time Gordon Gould, a graduate student at Columbia University, was working on his

doctoral thesis about energy levels of excited atoms of thallium. Whilst working on the thesis, he

developed some ideas and made notes about “laser” in November 1957. In his notes, he also

suggested using an open optical resonator, which became an important part of future laser systems

(en.wikipedia.org, 2008).

Gould also made the name “laser” for the first time. He first introduced the term “laser” to the public

in his 1959 conference paper “The LASER, Light Amplification by Stimulated Emission of

Radiation.” Gould’s idea was that “aser” to be a suffix and be used with an appropriate prefix

depending on the spectra of radiation emitted by the device. For example, xaser for x-ray emitting

devices, uvaser for ultra violet emitting devices, raser for radio-frequency emitting devices and so on.

Gould’s paper also included possible applications for a laser, such a spectrometry, interferometry,

radar and nuclear fusion. Afterward he continued working on developing his ideas further

(en.wikipedia.org, 2008).

Theodore H. Maiman made the first working laser in 1960, at Hughes Research Laboratories in

Malibu, California, beating several other research teams including those of Townes at Columbia

University, Arthur Schawlow at Bell Laboratories, and Gould at a company called TRG (Technical

Research Group). Maiman used a solid-state synthetic ruby crystal pumped by a flash lamp. His

system had a three energy level pumping scheme, and produced red laser light at 695 nanometres

wavelength (school-wikipedia.org, 2008).

The ruby laser became the first medical laser, when it was used in 1963 to coagulate retinal lesions.

(Lee, S; 2007)

An Iranian physic scientist called Ali Javan, made the first gas laser in 1961, using a mixture of

helium and neon. Javan later received the Albert Einstein Award in 1993.

Javan also developed the concept of semiconductor diode laser working with Basov (school-

wikipedia.org, 2008).

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1.2 Recent innovations

Since laser was first developed to this day, scientists have been constantly researching, developing,

and improving the laser technology. They have been continuously introducing different concepts for

producing different laser systems, different types of laser beams. They have discovered new materials

that emit different wavelengths, and have increased the number of various possible ways of exploiting

laser light. They have put the greatest of efforts in advancing the laser systems, making the

efficiencies of laser machines better and better, improving lasers’ power, and increasing our

knowledge and abilities in the fields of laser more and more. And the rewards have been great.

Now laser researchers are able to produce a wide variety of improved and highly specialized laser

systems, designed and optimized for different performance goals, including:

New wave length bands

Maximum average output power

Maximum peak output power

Maximum output pulse duration

Maximum power efficiency

Maximum charging

Maximum firing

(Laser Systems Product Group of AMT, 2008).

Laser systems can also be produced in all different sizes. Scientists are now capable of making lasers

in the whole range of sizes from microscopic diode laser with numerous applications, to football field

sizes neodymium glass lasers used for intertial confinement fusion, nuclear weapon research, and

other high energy density physic experiments (en.Wikipedia.org, 2008).

Some laser research laboratories are now able to create ultra-short, very high intensity laser pulses.

The world most powerful laser was developed at the Lawrence Livermore Laboratory in 1998 and it is

capable of producing laser pulses with output power of 1300 tetra watt. These high intensity pulses

can produce filament propagation in the atmosphere(en.Wikipedia.org, 2008).

Another laser research laboratory called The National Ignition Facility is working on a new laser

system that, when complete will have an output power of 700 tetra watt and will contain a192-beam,

1.8 mega joule laser system adjoining a 10-metre diameter targeting chamber. The system is expected

to be completed in April 2009 (cut-tec.co.uk, 2008)

Research for new lasers will continue. The age of laser is upon us.

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2. General principles and physics of laser

The term “laser” was first developed by Gordon Gould and is an acronym derived from the phrase

Light

Amplification by

Stimulated

Emission of

Radiation

The term has since entered the English language as a standard word, laser, losing the capitalization in

the process. The back-formed verb to lase means to “produce laser light” or possibly “to apply laser

light to” (cut-tec.co.uk, 2008).

In analogy with optical lasers, a device which produces any electromagnetic in a coherent state is also

called a “laser”, usually with the indication of type of particle as prefix (for example atom laser,

electron laser).

In most cases laser refers to the source of the coherent photons or waves, i.e. light or other

electromagnetic radiation (schools-wikipedia.org; 2008)

It should be mentioned that the word light in the acronym Light Amplification by Stimulated

Emission of Radiation is typically used in an expansive sense, as photons of energy in any radiation; it

is not limited to photons in visible spectrum. Hence, there are radio-frequency lasers, infrared lasers,

ultraviolet lasers, x-ray lasers, etc.

A good knowledge and comprehension of the general principle and physic behind laser, also thorough

understanding of the special properties of laser beam is very important for a laser therapist or

physician. It enables him/her to better appreciate the laser technology, and fully understand its

capabilities, possibilities, and limitations. It also gives the therapists the ability to devise the best

treatment plan; use the most appropriate techniques, and choosing the most suitable parameters for

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each individual client. It allows the therapist to modify the treatment plans, techniques, or parameters

depending to each client’s needs. This will facilitate a safe, efficient, and successful laser treatment.

So, let us discuss the properties and characteristics of laser and pulsed light first, and then we will go

into their principles and physic.

1.1 Properties of laser and pulsed light

Laser light produced by all different laser system, have four basic properties in common, which

separate lasers from ordinary light sources. The council for scientific and industrial research, CSIR, in

its published work called “The basics of laser physics,” explains these properties of laser as followed:

Monochromaticity –the light emitted by a laser device or the laser beam is monochromatic.

This means all the photons present in the laser beam have the same wavelength and

frequency. The laser light has a precisely defined wavelength because of the way in which the

laser is constructed. In contrast, ordinary pulsed light produced by a flash lamp is

polychromatic. This means the pulsed light is consisted of a combination of many different

wavelengths (colours).

Polychromatic radiation

Monochromatic radiation

Directionality- laser light is collimated or non-

diverging. Laser devices emit a relatively narrow beam in a very specific direction. Therefore,

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Picture1

(Physic world.com/laser, 2008)

the produced laser beam is directional and focus with all the waves( or photons) in the laser

light travelling at the same direction and parallel to each other. In contrast, the pulsed light

from light bulbs and flash lamps are very diverging. Ordinary pulsed light is emitted in every

spatial direction away from the source. The waves in the pulsed light diverge away from each

other.

picture1 (physicworld.com/laser, 2008)

Coherence – the laser light is coherent which means all the wavelengths of the laser light are

in phase in time and space.

Brightness – it is defined as the power emitted per unit area of the output mirror. In other

word, a laser’s brightness is the intensity in the laser beam divided by the emission line. A

laser produces unbelievably bright light. Fox (2008, p.4-5) explains that the great brightness

of laser arises from two factors. Firstly, the light in a laser system is emitted in a well-defined,

very focus and narrow beam. Therefore, the power per unit area of the beam is very high,

even though the total amount of power can be rather modest. Secondly, the laser light is

amplified many times before it is allowed to leave the lasing system.

These two factors mean the brightness of laser is extremely high in comparison to

conventional light sources i.e. light bulbs or white light. For example, a laser beam with 1mW

power has a spectral brightness that can be easily millions of times greater than that of a

100W light bulb. An ordinary light bulb works at a few thousand degrees centigrade. To

produce the brightness of a laser beam, an ordinary light bulb would have to reach impossible

temperature of millions of degrees centigrade.

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These unique characteristics of the laser light make it a very useful and effective for medical and

clinical applications.

2.2 Physic of laser

Laser beam can be described as a series of electromagnetic radiation that have the same wavelength,

frequency, and travel at a constant speed. The light waves have been described as electromagnetic

waves, because they have both electrical and magnetic components (Campbell, 2008).

As laser is a monochromatic electromagnetic radiation, it has a specific wavelength. Wavelength is

defined as:

“The distance between successive points of equal amplitude and phase on a wave i.e. trough to trough

or crest to crest” (Campbell, 2008).

Picture 3 (Campbell, 2008)

Aforementioned laser is electromagnetic wave, so it has a frequency too. Frequency as defined by Fox

(2008), is the number of waves that pass a given point in one second. The frequency can be describes

as the number of cycles per second.

As an electromagnetic wave, laser can have any wavelength within the electromagnetic spectrum.

This means it can have a very wide range of wavelengths that stretches from long radio waves,

through microwaves, infrared, visible light, ultra violet waves, and X-rays to ultra short wavelength of

gamma rays (en.wikipedia.org, 2008).

The wavelength of the electromagnetic waves has an inverse relationship with the frequency and

energy. The longer the wavelength, the lower its frequency and energy will be and vice versa

(physicworld.com, 2008).

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l wavelength

It is important to remember because laser can be made emit radiation over a very large part of

electromagnetic spectrum not only the visible region. As the visible light makes up only a small part

of electromagnetic spectrum, so many laser devices produce laser beams, which is not visible, the

human eyes.

Spontaneous emission

All atoms and molecules can give off radiations if they become excited by heat, light, electricity or

any other source of energy. The way a particular atom or molecules does this and the type of radiation

it gives out, is unique to that particular type of atom or molecule; and depends on its atomic or

molecular structure. Every type of atom or molecule has a different atomic and molecular structure

and emits only a specific type of radiation with a certain wavelength when it is excited. Therefore, the

wavelength of the radiation emitted by an excited atom or molecule is a very good indication of its

structure (mwit.ac.th/physicslab, 2008).

Several physic scientists and researchers in their book on quantum physics of atoms and molecules,

have analyzed the concept of spontaneous emission in details, including Eisberg and Resnick (1985,

chapter 4). It has been indicated that normally all the atoms and molecules within a material are at rest

at a stable lower energy level, called “ground state. When they absorb electrical, optical, thermal, or

any other form of energy, they can get excited, meaning that their energy level is boosted to a higher

energy level. But excited atoms or molecules are very unstable at the higher energy level (E*), and

tend to spontaneously fall back into their preferred and stable level of ground state (E°) within a tiny

fraction of a second. As the atoms or molecules fall down to a lower energy level, they release the

absorbed energy in the form of photons (photon can be visualized as small packet of energy) or short

trains of electromagnetic waves. This way the excited atoms or molecules emit electromagnetic

radiations. This process is referred to as spontaneous emission of radiation.

Picture 4

(Kwok-sang, 2007)

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The wavelength of the radiation given off by an atom or molecule depends on the difference between

the upper and lower energy levels of that atom or molecules. The greater the energy difference, the

shorter the wavelength of the radiation given out. Usually in atoms the higher and lower energy levels

are quite a long way apart, and the energy difference between the higher and lower are quite great. So

the laser systems or lamps that operate using atoms tend to emit radiation in the near infrared or

visible region of the electromagnetic spectrum (Fox, 2008).

As we know, each atom has of a nucleus, which is consisted of sub-atomic particles: protons and

neutrons. Moving around the nucleus, are the atom electrons. Normally each electron moves around

the nucleus at a particular orbit. Each orbital level has a specific energy level.

When a photon of energy interacts with an atom, it is the electron absorbs the energy, and gets

excited. When excited, the electron moves to a higher energy orbital level. However, the electron is

not very stable in higher energy orbital level, and very quickly moves back to its preferred orbit,

releasing the energy as it does so.

Picture 5 ( physicworld.com, 2008)

The electrons of molecules also can get excited in the same way, and emit high frequency radiation in

near infrared or visible light part of electromagnetic spectrum too. However, molecules have some

other types of energy level as well. The molecular energy levels are related to the way the atoms that

make up the molecules, are positioned and move in relation to each other. The atoms that make up a

molecule can move to and from each other (molecular vibrational motion) or they can move around

each other (molecular rotational motion). The difference of the energy level between different

quantum state of molecular vibration is less than the energy difference between orbital levels of

electrons. As the result, the radiation released by the molecular vibrational motion, is in the infrared

part of electromagnetic spectrum. The difference of energy level between different quantum states of

molecular rotation is even less than the molecular vibration, so the radiation given off by the

molecular rotational motion is usually in microwave part of electromagnetic spectrum

(mwit.ac.th/physicslab, 2008).

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Picture 6 ( physicworld.com, 2008)

In a flash lamp, most of atoms are excited to many different energy levels, and some of them reach the

highest energy level. Of course, each atom only spends only a tiny fraction of a second in an excited

state. Soon it emits energy and falls back to a lower energy level.

In a flash lamp, each excited atom gives off photon in its own accord and independently from other

atoms, but at any given moment in a glowing lamp, there are more atoms in the lower energy levels

than at higher levels.

The above two factors mean that the radiation emitted by different atoms can have different

wavelength, therefore the emitted waves are not in time with one another, instead they are all jumbled

up (physic2000.com, 2008).

Stimulated emission

In a laser a different situation to a flash lamp occurs, which is referred to as stimulated emission in

quantum physic. Lee .S, MD, in his paper called “Lasers, general principles and physics,” describes

the concept of stimulated emission in an easy to understand way. He explains when a photon

(containing high enough energy) strikes an atom at its ground state (E°), it causes the atom to go to its

higher energy level (E*). If a second photon strikes the atom at the E* level, the atom emits two

photons of the same frequency and in the same direction, as it returns to its ground state E°. So if on

their brief descent from E* to E°, the excited atoms or molecules at the E* are further bombard with

the same energy that caused the initial transition from E° to E* or a proportional amount, the net

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result is the liberation of an amount of energy twice of the original. This emission occurs in phase

(coherence) with and in the direction as the first bombarding photon. This process is called stimulated

emission. (Lee, 2008)

Picture 7 (Lee, 2008)

These two photons move off travelling in the same direction, with the same frequency and in phase

with each other. Then they will strike two more excited atoms in the E*energy level. So within a

small fraction of a second the process has been repeated many times. As all these waves are all in

phase with each other, they will reinforce each other. This way the radiation is amplified.

Picture 8 (Wilfrid Laurier University, WLU, physics

lab, 2007)

Population inversion

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In order for the stimulated emission process to start and continue, there must be enough number of the

excited atoms in the higher energy level E*. In fact if there are more atoms at the ground state E° than

there are at the higher E* level, as there are in a flash lamp, then the energy we discharge into the

lasing material will be mostly absorbed by the atoms at the ground state E° to go to higher energy

level E*. Therefore, the loss will be greater than the gain and the energy we put into the system will

not be amplified (Johansson, 1995).

The key to solving this problem when producing laser, is the concept of population inversion.

Johansson (1995) explains that if we put very intense and high amount of energy into system fast

enough, then a very large number of atoms will be excited into high energy E* level. Then it will be

possible to achieve a situation when the number of atoms in higher energy E* level is greater than the

number of atoms in the ground state E°. This situation is referred to as population inversion.

Picture 9 ( Fox, 2008)

At this point any more photons of energy that are put into the system, it will strike the excited atoms

at the high energy level E*stimulating them to fall back into ground state E°, emitting two photons of

the same wavelength. Soon chain reaction of stimulated emission will start and in fraction of a

second, this chain reaction produces a powerful eruption of a coherent beam of radiation: a laser.

So far, we have thought of the stimulated emission occurring in a laser system, as being in a simple

two-level system like that shown in picture 8. However, in reality a laser operating through such a

two-level system is very unusual. Johansson (1995) explains the reason is that, under equilibrium

conditions, energy level E2,has a negligibly small population, which is a much lower population than

energy level E1has. Pumping the system with energy E2−E1, will result, initially, in net absorption,

which will continue until both populations are equal, a condition known as saturation. At this point,

any further pumping will result in absorption and induced emission occurring at the same rate.

Therefore, population inversion cannot normally be achieved.

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To overcome this problem and in order to achieve and obtain population inversion, usually a system

with a minimum of three energy levels is necessary. In such system, there is a semi stable higher

energy levelE2, between the ground state energy level E1and the highest energy level E3.When atoms

reach this semi stable level, they become more reluctant and remain there for slightly longer than

other levels before falling back into the ground state. The population inversion then is achieved

between levels 2 and 1, by pumping the 3-1 transition. The level 3 to level 2 transition process must

be efficient and very fast in order to build up the population of level 2, while the population of level 1

is depleted. This way, in these types of multilevel systems achieving and maintaining the population

inversion, is much easier. Lasing then can occur in the level 2 to level 1 transition

Picture 9 (Kwok-sang, 2008)

Picture 10- three-level laser system (Kwok-san, 2008)

In more complex laser systems, there are even more energy levels than three. Commonly a four-level

or five-level systems are used.

a) A five- level laser b) A four- level laser

Picture 11 (WLU, 2007)

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2.3 Design

A basic laser device is consisted of three principle components:

1. An active laser medium or gain medium

2. A laser cavity or an optical resonator

3. An energy source or a pump

(Lee, 2008)

The active laser medium or gain medium converts and amplifies the input energy into the laser beam

by the quantum process of stimulated radiation, discovered by Albert Einstein while researching the

photoelectric effect. It is material of controlled and specialized purity, size, and shape, which can be

solid, liquid, or gaseous. Different active mediums emit radiation with different energies and

wavelengths (en.wikipedia.org, 2008).

The active medium is energized; its atoms become excited to higher energy quantum levels, and a

population inversion is induced by the energy source. This process is called pumping and the energy

source is referred to as a pump. The energy the pump discharge for absorption by the active medium,

might be in the forms of electrical, thermal, optical or chemical energy

(school-wikipedia.org/wp/l/laser, 2008/9)

The laser cavity is a vacuum tube or box, which contains the active medium and makes an oscillator

from an amplifier. The laser cavity does this by having two parallel mirror or reflectors facing each

other at each end the tube. The reflecting surface of one these mirror is coated with special material to

be 100% reflective at the specific laser wavelength. The other mirror is coated so it is partially

reflective and allows 1 to 10% of the radiation to leak out of the laser cavity as the laser beam (Lee,

2008).

The distance between the two mirrors must be an integral number of half-wavelength necessitating

extremely accurate measurements. This ensures that the radiation will be amplified in the same phase.

Because the radiations that travel in opposite directions, meet in between the mirrors. If such

radiations are out of phase when they meet, they will interfere with each other. In contrast, if they are

in phase with each other as they meet; they will enforce and amplify each other (Johansson, 1995).

Johansson (1995) also explains the process, which amplifies the radiation within the laser cavity.

When the active medium emits photons by the means of stimulated emission, these photons are

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reflected back and forth between the two mirrors many times. Each time a wave is reflected from the

mirror it meets other waves, which are moving towards the mirror, and as they are in phase, they will

be amplified. In addition, each photon passes through the active medium many times before it leaves

the cavity. Each time it passes through the active medium it collides with one of the active medium

atoms in the excited state. These collisions stimulate the atoms to emit photon. As other photons,

collide with other excited atoms in the same way, the radiation energy inside the resonator builds up

to a very high level very rapidly and is amplified exponentially by reflection between the parallel

mirrors.

Picture 12 ( El Rouby, 2007)

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Picture 13- the basic constructional design of a laser system (El Rouby, 2007)

2.3 Laser types

Lasers can be categorised by two criteria: by the mode of operation and type emitted laser beam; and

by active medium used.

By radiation:

Laser devices can generate and deliver laser beams, in general, in two ways: as a constant and

uninterrupted flow of radiation (called continuous wave laser or CW laser) or as multiple discrete

pulses of radiation (called pulsed laser).

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These two types are fundamentally different in design, operation, and the output beam. Lee (2008)

about the properties of each of these laser modes, states that:

In a continuous wave or CW laser, energy is continuously pumped into the active medium in

a way that it achieve and maintain an equilibrium between the number of atoms that are

excited and boosted into higher energy levels and the number of the photons emitted from the

excited atoms. In such equilibrium, a continuous laser output with a stable average beam

power is produced. The duration of each laser emission is approximately 0.25 s. With such a

long duration and with the constant delivery of energy to the tissues, significant tissue

destruction happens. To reduce the extent of their thermal damage, CW laser devices have

been modified to utilise a electronically controlled, timed shutter. These shutters operate

mechanically and like a gate that can be preset and timed to prevent the output of laser beams

in regular intervals. This way the laser beams are sent out in a pulsate pattern. However, they

are not a real pulsed laser and the average beam power during the period each output is

constant. They are just chopped off physically.

In pulsed laser, the power of the output beam varies with respect to time, usually taking the

form of alternating “on” and “off” periods. In other words, the laser is emitted in multiple

discrete pulses, which usually are broad and randomly shaped. Pulsed lasers have pulse

duration or pulse width of tens of milliseconds to just a few milliseconds. This type of laser is

sometimes referred to as long pulse laser.

In many applications we need to deposit a very large amount of energy in as short time as

possible. For example in laser ablation, only the top layers of the incident tissues evaporate if

they receive the required energy in a very short time. However, if the same amount of energy

is delivered over a longer period, the heat will have time to be transferred to deeper layers of

tissue and will cause thermal damage and less of the surface layers will evaporate. Therefore,

some laser devices are designed to produce very intense, very high-energy beams of laser in

ultra short pulses, between 10-25 ns. These lasers are referred to as Q-switching lasers. In Q-

switching lasers, photons are prevented from being reflected back and forth between the

cavity mirrors. This is done by placing a very high speed, electrically sensitive, and

polarisable optical shutters called Pocket cell, the 2 mirrors. Because the photons cannot

resonate in the laser cavity, the stimulated emission will not start. This allows the population

inversion to build up and reach a maximum level. Then the Pocket cell opens and allows the

photon to oscillate back and forth again. Subsequently the stimulated emission starts. And as

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the population inversion has been built to maximum potential energy level, it generates a very

intense and very powerful laser beam.

By the active medium

Maiman used a synthetic ruby crystal when he invented the world first laser. Once the first laser was

made, the floodgate opened. Within a few short years, laser research at industrial labs and universities

grew in various directions, as did the laser industry. Since then to now, hundreds of different lasers

have been made, hundreds of different active medium have been used to produce thousands of

different wavelengths in the electromagnetic spectrum from far infrared through visible light to ultra

violet and even x-ray.

However, all these different active mediums are categorised (geocities.com/ laser_types-

_and_classifictions, 2008), as followed:

Solid-state lasers:

In these laser systems, the active medium has been distributed in a hosting solid matrix. The host

material is generally a type of crystal or glass. The distributed active medium or dopant, are usually

rare earth elements. Solid-state laser are usually optically pumped.

There are many different type of solid lasers produced. Examples of some of the most common ones

are: ruby laser, Alexandrite laser, Nd:YAG, Erbium:YAG.

Gas lasers:

The gas lasers are one of the oldest types of lasers. In these types of laser, the active medium is a type

of gas that fills the laser cavity. These days variety of gas lasers are available and are used for various

purposes. Gas lasers are made with many different gases, but the most common ones includes helium

laser, helium-neon laser (He-Ne), argon laser, Co2 laser.

Excimer lasers:

20

The name Excimer is derived from the terms excited and dimmers. These laser systems, use a reactive

gas such as chlorine or fluorine mixed with an inert gas such as argon or xenon. When electrically

stimulated, a special type of excited molecule called dimer is produced and when lased it emits laser

beams in ultra violet range.

Semi conductor lasers:

In these lasers, a type of semi conductor material is used as an active medium. Semi conductor lasers

are very power efficient and economical to operate. They can be built in very small and compact

sizes. Therefore, they are the most commercially used lasers these days.

Dye lasers:

Dye lasers use different types of complex organic days such as rhodamine 6G in a liquid solution or

suspension as their active medium. Dye lasers are highly tuneable and can be adjusted to produce a

broad range of wavelength or ultra short pulses (as short as a few femtoseconds).

Free electron lasers:

Free electron lasers, also referred to as FELs, generate coherent, high power radiation that is

widely tuneable, currently ranging in wavelength from microwaves, through infrared, to the

visible spectrum, and to soft X-rays. They produce the widest frequency and wavelength range of

any laser type. Laser beams generated by FELs, have the same optical traits and properties of

other lasers, however the fundamental of FELs’ operation is very different. While other laser

systems operate on the principle of bound atomic or molecular states, FELs use a relativistic

electron beam as the active laser medium, hence the name free electron

(school-wikipedia.org/wp/l/laser, 2008/9).

21

3. Skin and light interaction:

When skin is the incident site for radiation (i.e. visible light), three distinctive phenomena occurs: skin

reflects scatters or absorbs, and transmits (penetration of radiation into skin) the radiation. All three

mechanisms take place to varying degrees and proportion upon any skin and radiation interaction. The

degree and percentage of light reflection, absorption, and scattering; determines the depth of

penetration (Bassel, 2007).

When radiation hits the skin it must pass through stratum corneum, before it can reach underlying and

viable tissues. Factors such as the thickness of the stratum corneum, its composition, and morphology

affect the amount of radiation that pass through the stratum corneum. Research has shown that “for

normally incident radiation, the regular reflectance of an incident beam from normal skin is always

between 4% and 7% over the entire spectrum from 250-300 nm, for both white and black skin

(Anderson. R. R; 1981).

Anderson believes within any layer of skin around 93% to 97% of any incident radiation not returned

by normal skin reflectance, may be either absorbed or scattered by skin. These two process taken

together essentially determine the penetration of radiation into skin.

Optical scattering is an interaction of light as it passes through matter in which the direction of the

incident rays is changed by the molecules and other small particles present within the medium.

Scattering plays an important role in spatial distribution of the absorbed energy (interaction of laser

beam with living tissue, 2008).

Anderson (1981) state that scattering results from inhomogeneities in a medium’s refractive index,

corresponding to the physical inhomogeneities. The distribution and intensity of light scattering

depends on the size and shape of inhomogeneities and relative to the wavelength. He believes that

scattering by the collagen fibres to be of major importance in determining the depth of penetration of

optical radiation within the dermis.

Radiations are absorbed by the chromophores present in the skin structure. Chromophore refers to

any particle, substance, or cell, which can absorb the radiation strongly. Once photons enter the skin,

they are absorbed by the chromophores within the skin, and the energy of the photon is transferred to

the chromophores and the photons no longer exists (Bassel, 2007).

22

There are three main endogenous chromophores present within skin: melanin, oxy-haemoglobin, and

water. Other endogenous chromophores include riboflavin, bilirubin, protoporphyrin IX. An example

of exogenous chromophores is tattoo ink. The level of absorption of radiation by the skin is

determined with the type, concentration, amount, and distribution of these chromopohores present in

the skin, which vary between individuals and between anatomic location of target tissue (Anderson,

1981).

Absorption is a function of chromophores and wavelength. An important characteristic of these

chromophores is that they are wavelength dependant. Different chromophores have different

absorption coefficients for different wavelength.

Absorption and penetration of radiation have an inverse relationship. The more a radiation is absorbed

by the skin’s chromophers, the less it can penetrate into the skin.

Therefore, the level and depth of penetration is determined by the level of corneal, epidermal, or

dermal absorption; and the thickness of the skin and the wave length of the radiation.

Absorption coefficient is a measure of the degree of absorption by the chromophores at particular

wavelength (Lee, S. 2007).

Picture 14 – absorption spectra of major skin chromophores

(Hsein Jen, 2004)

As the table above ( Hsein Jen, C.T. 2004) demonstrates, in near infrared (770-1100 nm) and red

wavelength melanin is the dominant chromophore. The melanin absorption coefficient increases

towards the ultra violet end of spectrum. Therefore, the short wavelength ultraviolet, violet, and blue

23

lights are strongly absorbed by melanin in the epidermis level, and cannot penetrate deep into skin.

The absorption coefficient of melanin decrease as we move towards the longer wavelength region of

red and near infrared, which can explain the deeper penetration ability of red and infrared light into

the skin. At mild infrared (1200-300nm) and far infrared (3000-10000 nm) region of the spectrum,

absorption by melanin is almost negligible. However, at these regions water has a very high

absorption coefficient and absorbs the radiations very strongly. As most of body’s tissues including

skin, tissues are made up of water, so these radiations are absorbed very strongly with top skin layers.

That is why Co2 laser, which emits radiation in 10000nm part of spectrum, is used for ablative skin

resurfacing.

As mentioned before, the penetration depth of the radiation is wavelength dependant

Picture 15- penetration depth of different wavelength radiation

( Campbell, 2008)

As we can see in the table, the longer wavelength infrared and red lights can penetrate deep into the

skin, even down to subcutaneous layers. The penetration depth of the lights is decreased towards the

shorter wavelength blue, violet, and ultra violet lights. Almost, top skin layers absorb all of the near

ultra violet lights (UVA).

Generally over ultra violet, visible, and NIR spectrum, penetration increases with increasing

wavelength. It can vary from several micro metres in ultra violet region, up to several millimetres in

the NIR region.

24

Another important factor, which influences the depth of penetration of radiations and their photo-

biological effects on the tissues, is the radiation power.

Power density:

Power density (Pd) of a laser beam, refers to the intensity of the beam. The power density (Pd) of

laser beam is defined by Lee (2008) as the energy the beam delivers during one second into per unit

area of the incident tissue. Power density is measured by calculating the wattage of the laser beam per

diameter of the beam. This means, power density and the beam diameter have an inverse relationship,

as shown here:

Pd = (100 W) / d2

Here W is the laser power in watts, and d is the diameter of the laser beam in centimetres

(Lee.S.;2007).

The measurement unit for power density (Pd) is watt per centimetre square.

Fluence:

Fluence is an indication dose of the energy we have discharged into the tissue. Fluence is defined as

the total amount of energy we discharge into per unit area of the target tissue, every time we radiate a

beam of laser into that tissue (Frenz, 2002).

Fluence is time dependant. It means for a given wattage of the laser, the longer we radiate the laser

beam into the skin, the more energy we will deposit onto the skin (Lee, 2008).

Lee(2008) shows that Fluence is calculated as follows:

Fluence = Pd × t

Here t is the duration of exposure in second

Fluence can also be calculated as below:

Fluence = JA

25

Where J is the total energy amount of the laser beam in joules and A is the size of the cross-sectional

area of the laser beam in square metre(Lee, 2008).

The following then applies:

Fluence = JA

= Power (w )×Time (s)

Spot ¿(cm2) (bentlon.com, 2008)

The aforementioned factors and characteristics of light skin interaction are very important

considerations. As one, by choosing the power, energy, time, and wavelength of the laser, can have

control over the extend of photo-biological effect, the depth of penetration, and the tissue that will be

directly affected by the laser radiation. This allows the selective targeting of the chromophores in the

tissue depending on the aim of the treatment. This property is one of the underlying principles of the

concept of Selective Photo Thermolysis (SP).

Light can produce a photo-biological effect within the tissue with three different mechanisms by

thermal (by producing heat in the absorbing tissue), mechanical (by producing shock wave), and

photochemical by producing chemical reactions within the cells (interaction of laser beam with living

tissue, 2008).

With rare exception, lasers, IPLs, and VPLs used within beauty field, treat the skin by thermal

mechanism, which is producing localized heating at the sites of energy absorption.

3.1 Selective photo thermolysis:

Selective photo thermolysis is a fundamental concept for safe and effective treatments using lasers,

IPLs, and VPLs. It outlines the essential factors (fluence, wavelength, time, penetration depth) in

order to successfully and safely produce localized photo thermolysis.

Anderson and Parrish first introduced the concept of Selective Photo Thermolysis (SP) in 1983, when

they described the principles for producing discrete laser-induced positive thermal damage to specific

26

chromophre targets at the cellular level, in a way to minimize undesired thermal damage to the

surrounding tissues caused by thermal diffusion.

SP is a method used for producing:

Selective absorption of light by target chromophores

Confinement of the laser-induced heat to these target tissues

The first one is achieved by choosing the appropriate wavelength light for particular target

chromophores. In other word, if we choose a wavelength that is strongly absorbed by the

chromophores present in the target, but it is poorly absorbed by other chromophores present in the

surrounding tissues, then the most of the laser energy will be absorbed by the target’s chromophores.

this makes it possible to produce the required heat within the target structure without damaging the

surrounding tissues (Akita & Anderson, 2004).

The rate of thermal diffusion of a given tissue is called thermal relaxation time (T R) and is defined as

the time required by a given tissue, to lose 50% of its heat through thermal diffusion into surrounding

tissue(Lee, 2008).

It is measured in terms of the area affected and the thermal diffusivity (D) of the target tissue, as

follows:

T R= r2

4 D (Lee, 2008)

Where r is the radius of the target tissue.

Therefore, significant thermal diffusion (and hence thermal damage) to the surrounding tissues is

minimized if the duration of the laser pulse is shorter than the T R of the target tissue (Lee, S. 2007)

Thermal relaxation time and SP are not very complicated concepts. When a tissue is heated, it will

transfer some of its heat to the tissues around itself so its heat cools down. The time it takes for the

tissue to transfer a considerable amount of its heat to the other tissues is called thermal relaxation time

of the tissue.

Now, if we choose a laser pulse which has a duration shorter than thermal relaxation time of our target

structure (the structure which contains the absorbing chromophres), then the target structure will not

27

have enough time to transfer its heat to the other tissues around it. Therefore, the heat will remain

within the structure, producing positive thermal damage to the structure without damaging the

surrounding tissues.

Ideally, the pulse width or duration should be just below or equal to thermal relaxation time of the

target structure, to ensure a good heat confinement, but allowing the target to heat up sufficiently and

uniformly. A useful approximation is that the thermal relaxation time of the target in milliseconds is

around the square of its size in millimetre (Akita & Anderson, 2006).

Sadick and Weiss (2001) also suggest another important concept called “selective thermokenitic,”

which allows us to selectively cool down the skin surface without cooling down the target structure.

To do this, we choose pulse duration, which is longer than the thermal relaxation time of top

epidermis layers (3-10 milliseconds) but just below the thermal relaxation time of target structure.

Then we use a cooling mechanism on the skin surface. Because the pulse duration is longer than

epidermis thermal relaxation time, it allows the heat to be transferred from the epidermis to the cooler,

which facilitates the partial cooling of epidermis. Nevertheless, the cooling device will not cool the

target structure because the laser pulse duration is shorter than thermal relaxation time of the target

(Sadick, N.S & Weiss, R.A. 2001)

4. Clinical lasers and light sources

Lasers and light sources now are in use extensively and form a necessary, vital, and large portion of

clinical aesthetic procedures, and it is constantly growing and evolving.

Laser and light technology and optic of skin science have steadily advanced during past couple of

decades; and now facilitate treatments of many different skin conditions including a host of vascular

and pigmented lesions, wrinkles, tattoos, scars, acnes, hirsutism, hypertrichosis, superflus and

unwanted hair (Lee, 2008).

The most common laser and light source systems currently being used for cosmetic procedures are:

Ruby lasers

Alexandrite lasers

Semi-conductor diode lasers

Nd:YAG lasers

28

Er:YAG lasers

Co2 lasers

Argon lasers

Pulsed dye lasers

Exogenous chromophore –assisted lasers

IPL or Intensive Pulsed Light

VPL or Various Pulsed Light

Ruby lasers:

Ruby laser was the first ever laser made in 1960 by Maiman. It became the first medical laser as well,

when it was used 1963 to coagulate retinal lesions (Lee, S. 2007)

Ruby laser is a three level solid-state laser using a synthetic ruby crystal. It is pumped optically and it

produces pulsed beams of visible light with an intense red colour. There are two type of ruby lasers

available: normal mode ruby laser (or long pulse ruby laser) which has a pulse duration in the range of

millisecond, and Q-switching ruby laser which produces high power, intense, ultra short pulses with

duration range of nanoseconds (Johansson, 1995). Wavelength of ruby lasers is 695 nm. Light in this

wavelength spectra are heavily absorbed by the melanin. This makes ruby lasers very effective in

treatment of melanin rich structures such as hair and skin pigmented lesions.

Long pulse ruby lasers are one of the most effective and commonly used lasers for hair removal. Ruby

laser light does not penetrate in the skin as deep as other lights in the red and infrared region if

electromagnetic spectrum (hair laser removal.co.uk, 2008).

As the result of these two characteristics of ruby laser light (very high absorption coefficient by

melanin, and less depth of penetration) it is absorbed too heavily by melanin rich top epidermal layers

of darker skin. This will damage the melanocyte cells and can cause hyper or hypo pigmentation

condition in dark skinned people. It also creates too much heat too near the skin surface and can cause

skin burn. In addition, the thick black hair of darker people has a much higher absorption coefficient

than finer brown hair, and 695 nm ruby light, which, can heat up these hair shafts to such a high

temperature that can cause extensive thermal damage to skin tissue around the hair follicle. Therefore,

ruby laser is not suitable for the treatment of skin types IV, V, and VI (Lepselter & Elman, 2003).

However, the high absorption coefficient wavelength 695 nm by melanin (the highest among red

sufficient temperature for positive damage will be reached for effective hair removal in fair people.

The little amount of melanin means there will not be a risk of skin burn of pigmentation destruction.

29

This has made ruby laser one of the most effective lasers for removal of lighter hair (Haedersdal &

wulf, 2004).

High power, ultra short pulses of Q-switching ruby lasers, along with high melanin absorption and

less penetration of wavelength 695nm, mean this type of laser are very effective for treatment of

epidermal pigmented lesions such as lentigines and freckles and tattoo removal specially blue-black

tattoos and some green inks (skin laser directory.co.uk, 2008).

The best -known ruby laser systems currently in the market are The Ruby Star (Aesculp-Meditec;

Jena, Germany) and the Sinon ruby laser (Wave light; Erlangen Germany) which both are dual-mode

lasers ( Dierickx, 2006).

Alexandrite lasers:

Alexandrite laser is a four level, optically pumped, solid state laser that produces visible red pulsed-

lights with the wavelength of 755nm (Johansson, 1995).

Alexandrite laser systems are available in two types of normal mode and Q-switching. It uses the

same mechanisms of ruby laser, and the light it generates has similar properties to ruby light.

Dierickx (2006) suggests that the longer wavelength of 755 nm means alexandrite laser can penetrate

deeper into skin than ruby laser, and the ratio of energy deposited in the dermis to the epidermis is

greater with alexandrite laser. Therefore, the risk of epidermal damage is smaller with alexandrite

lasers.

Alexandrite lasers are also more power efficient. As the result, they have replaced ruby lasers in the

terms of popularity and the width of spread. Five different alexandrite lasers are currently available in

the market: Apogee (Cynosure; Chelmsford, Mass), Epitouch Alex (Lumenis; Santa Clara, Calif),

GentleLase (Cadela; Wayland, Mass), UltrawaveII-III (Adept Medical; Rancho Santa Margarita,

Calif), and Epicare (LightAge, Somerset, NJ) (Dierickx, 2006).

Diode lasers:

Diode lasers use a solid semi-conductor material as the active medium. The semi-conductor active

medium is pumped by electrical discharge and it produces laser light in near infrared and into visible

30

red region of the spectrum. Diode laser is a pulsed light with the wavelength of 800-840 nm

(Johansson, 1995).

At 800 nm wavelength, diode laser can penetrate into skin more deeply than ruby or alexandrite

lasers, so there is less risk of over-heating and epidermal damage, so individual with darker skin types

(V-VI) can be treated more safely with diode laser systems. In general, diode lasers have been found

to be very effective for various skin treatments, and to produce impressive result while they are much

better tolerated by patients with darker skin types (Fiskerstrand & Svaasand & Nelson, 2003).

Diode lasers can be designed to produce very high power laser beams with broad range of pulse width

from 5-1000 milliseconds (Johansson, 1995).

Semi-conductor lasers are some of the most efficient of all lasers, with an energy efficiency of about

30%, so they are very economical to run. In addition, they can be manufactured in very compact sizes

and are very lightweights (Johansson, 1995). As result, diode laser systems currently are one the most

popular and most widely used laser devices in the cosmetic and beauty clinics.

Many different diode laser devices have been approved by FDA, for cosmetic procedures and are

available in the market now including: LightSheer XC, formerly Coherent Medical, now Lumenis’

Sanata Clara, Calif; Apex-800, Iridex, Mountain View, Calif; F1 diode laser, Opus Medical,

Montreal, Canada; Mediostar, Asclepion-Meditec, Jena, Germany; EpiStar, Nidek, Gamagori, Japan

( Dierickx, 2006).

Nd:YAG lasers:

Nd:YAG is a solid-state laser, which uses Neodymium-doped yttrium aluminium garnet as the active

medium. Nd:YAG is pumped optically and it emits laser radiations in infrared region of

electromagnetic spectrum with wavelength of 1064 nm (Johansson, 1995).

At this wavelength Nd:YAG laser can penetrate deep into dermal layer of the skin. In fact Nd:YAG

laser has the deepest penetration in comparison to all other clinical laser systems.

Long wavelength of Nd:YAG increases the ratio of energy deposition in the dermis to the epidermis,

which results in reduction of epidermal heating. However, the absorption coefficient of melanin at

wavelength 1064nm is lower than other infrared or red parts of spectrum. The reduced melanin

absorption at this wavelength, necessitates the need for high fluencies in order to adequately induce an

effective positive epidermal or dermal damage ( Dierickx, 2006).

31

The deep penetration into dermis and poor melanin absorption alongside with an epidermal cooling

system, make the Nd:YAG lasers potentially the safest laser system for treatment of darker skin types

up to VI. Currently Nd:YAG lasers are the most commonly used lasers for treatment of skin photo

types IV, V, and VI in the cosmetic field due to its high safety profile. It is also the laser of the choice

for treatment of pseudofolliculitis barbae and other skin conditions commonly seen in people with

darker skin types. However, poor melanin absorption in Nd:YAG lasers also means they are not

effective for removal of fine or light hair, and are not as effective as other laser systems for hair

reduction treatments (Lepselter & Elman, 2003).

However, the reduced melanin absorption means very high fluencies (50-100 J/cm2) is required to

induce sufficient positive thermal damage for effective treatments.

There are two types of Nd:YAG lasers available: long-pulsed Nd:YAG lasers with pulse width in

milliseconds range and Q-switch Nd:YAG with very short pulse durations in the range of

nanoseconds. The long pulsed versions are most commonly used for hair reduction procedures on the

clients, while Q-switching types are commonly used for tattoo removal. So far 25 different types of

Nd:YAG lasers have been cleared by FDA for permanent hair reduction including: Gemini

(Lasescope; San Jose, Calif), CoolGlide (Cutera; Brisbane, Canada), SmartEpill (Cynosure,

Chelmsford, Mass), Athos (Quantel; Les Ulis Cedex, France), Dualis (Fotona, Ljubljana, Slovenia),

Varia (CoolTouch, Roseville, Calif), and Mydon (Wavelight, Erlangen, Germany) (Dierickx, 2006).

Co2 lasers:

`Patel at Bell Laboratories developed the Co2 laser in 1964. It emits invisible radiation in far infrared

parts of electromagnetic spectrum at wavelength of 10,600 nm. At this wavelength, light is heavily

absorbed by water, which is the primary constituent and choromophore of every cell within any living

tissue. Co2 laser can target both intracellular and extracellular water. When the light energy is

absorbed by water-containing tissues, skin vaporization occurs. Thus, the energy generated by carbon

dioxide laser can be used for cutting through or volume ablation of tissues. This unique characteristic,

makes the Co2 laser the most widely used medical laser today (Lee, S. 2007)

Co2 laser is the most commonly used laser for ablative skin resurfacing in dermatology. This laser

light is absorbed by water-containing skin cells within top skin layers, resulting in superficial tissue

vaporization with production of coagulative necrosis in the remaining dermis. If the sufficient energy

fluence is deposited into skin within a very short pulse duration (optimal pulse width <326μs ), there

will be extremely rapid temperature rise in the surface skin tissue, with almost no thermal diffusion

32

and minimal coagulation or residual thermal damage. The minimum energy fluence of 5 J/cm2is

necessary to exceed the vaporization threshold of the targeted skin (Bader, R, S. 2007).

Two different carbon dioxide laser technologies can deliver the energy needed for skin vaporization in

less than one millisecond. One is to use an ultra short pulsed high energy laser or Q-switching laser.

The other uses a computer-controlled photo-mechanical shutter system, which flash scans a

conventional continuous waveCo2 laser beam so rapidly that the emitted light is prevented from

contacting skin for more than 1millisecond (Bader, R S. 2007)

Er:YAG lasers:

Er:YAG laser system use yttrium-aluminium garnet doped with erbium as the lasing medium, which

emits laser radiation in far infrared region of the electromagnetic spectrum with wavelength of 2940

nm (Johansson, 1995).

This wavelength is heavily absorbed by the water contents of skin tissues, resulting in tissue ablation.

Er:YAG laser was developed in response to the demand for less aggressive modalities of ablative skin

rejuvenation (El Rouby, 2007).

At 2,940 nm wavelength, Er:YAG laser is absorbed 12-18 times more efficiently water-containing

superficial skin tissues than carbon dioxide laser. In addition, it has a ultra short pulse width of

250μsec, and at fluence of 5 J/cm2 , Er:YAG laser ablates about 5-20μm of tissues per laser pass, with

minimal residual thermal damage, whilst Co2 laser ablates about 20-60μm of tissues with up to

150μm of residual thermal damage. Therefore, Er:YAG laser is a much less aggressive ablative laser

with much better side effect profile (Tanzi, E L. 2006).

But the downside is that Er:YAG lasers produce less impressive clinical improvement of the skin

than Co2 lasers, and the induced tissue tightening effect is reduced in Er:YAG lasers.

However, recently modulated Er:YAG laser systems (which utilise both short and long pulsed

modes)have become available. These new lasers have deeper tissue ablation ability, and can achieve

better collagen remodelling results, with added possibility of more significant tissue coagulation (El

Rouby, 2007).

All together, new modulated Er:YAG laser systems combine a precise controlled tissue ablation with

the ability to induce formation of dermal collagen by means of thermal injury, therefore achieving

impressive skin rejuvenation (Akita & Anderson, 2004).

33

Argon lasers:

Argon laser was first developed in 1962. Argon laser is a type of excimer laser that emits laser beams

in the blue –green region of the visible light at wavelength 488/514nm (Johansson, 1995).

The melanin has a high absorption coefficient at wavelength 488/514nm, so argon laser is absorbed

heavily by melanin present within epidermal layer of skin and cannot penetrate deep into skin.

Haemoglobin has a high absorption coefficient at this wavelength and absorbs the argon laser

strongly. Therefore, the effect of argon laser on the skin is superficial. Today, argon laser is used for

photo-coagulation (thermally obliterating without vaporization) of blood vessels in the treatment of

diabetic retinopathy and port-wine stains (Lee, S. 2007).

Pulsed dye lasers (PDL):

In pulsed dye laser or PDL, the stimulated emission of laser beam occurs in liquid solution or

suspension of fluorescent organic dye. DPL was invented by Sorokin and Lankard at the IBM

laboratories in 1966. They are unusual in that the active medium is a liquid. The dye solution is

optically pumped by a flash lamp. it emits pulsed laser beams in the greenish yellow part of visible

light (school-wikipedia.org, 2008/9).

. Early versions of PDL emitted laser light at wavelength 577nm with pulse duration of around 450

microseconds, which corresponds directly with the third main absorption peak of oxyhaemoglobin.

Consequently, PDL is primarily absorbed by oxyhaemoglobin present in blood vessels, therefore

selectively targeting the vascular lesions (El Rouby, 2007).

Over last decade, manufacturers have managed to extend the wavelength of PDL lasers to 585nm to

facilitate a deeper penetration without decreasing its absorption coefficient by haemoglobin. In

addition, the pulse duration has increased up to 1.5 milliseconds, making treatment of larger vascular

lesions possible (Goldberg, 2000).

Recently newer versions of PDL devices have been introduced into the market, with ultra-long

wavelength of 595nm, and the pulse duration is adjustable from 1.5 to 40milliseconds. They also

utilize a cryogen-cooling device to decrease pain and adverse effects. The new ultra-long PDL at

595nmcan provide an even deeper penetration than the 585nm version PDLs, making them more

effective at treating deep setting vascular lesions. In addition, as larger-calibre vessels require longer

pulse width to be destructed effectively, therefore by adjusting the pulse duration to the size of

targeted vessels, different-sizes vessels can be successfully treated (Nouri, K. 2008).

34

Today the PDL is considered as a kind of gold standard for treatment of port-wine stains, and

superficial haemangioma and variety of other acquired cutaneous vascular lesions such as

telangiectasias, cherry angiomas, and rosacea (Akita,2004).

PDLs are potentially safe and there is very low risk of adverse side effects, and it can be used to treat

infants aged only a few weeks.

PDLs are also successfully used for flattening and reducing the redness of scars and keloids. A low-

fluence PDL irradiation increases and stimulates dermal elastin (El Rouby, 2007).

Exogenous chromophore-assisted lasers:

In these methods instead of targeting a naturally occurring endogenous chromophore, an exogenous

chromophore is introduced into the skin tissues at the treatment site, and admitted into targeted

structure, then it is irradiated with laser at a wavelength that matches the peak absorption coefficient

of the exogenous chromophore. This method is suggested, that will eliminate the problem of

competing chromophores present in the skin. However, the main problem is finding a suitable

chromophore, which can be admitted reliably and distributed evenly throughout the whole depth of

the targeted structures (Morton, 2001).

One of the more common versions of this method is hair removal with carbon suspension Q-switching

Nd:YAG lasers. In so-called SoftLight technique (developed by ThermoLase; London, England), a

proprietary suspension of 10mm diameter carbon particles with a peak absorption coefficient in the

near infrared part of electromagnetic spectrum, is applied to the skin at the treatment area to enter the

hair follicles. Then the skin is irradiated with a Q-switching Nd:YAG laser with wavelength 1064nm,

and pulse width 10ns, using a 7mm spot size with relatively low energy fluence (about 2-3 J/cm2).

However, the problem seems to be that the ultra short nanoseconds duration of laser exposure and the

low fluence limits the extent of follicular damage (Dierickx, C. 2006).

Therefore, an immediate delay in the hair re-growth is observed following the treatment, but it does

not produce any long-term hair reduction.

35

Meladine

Recently, a new exogenous chromophore, called meladine, has been introduced to be used for

permanent hair reduction treatments. Medaline is a topical melanin-encapsulated,

phosphatidylcholine-based liposome solution, which is said to be able to selectively deposit melanin

directly into the hair follicle without staining the surrounding skin. This proprietary solution is

sprayed on the skin in the desired area. The liposome molecules are small enough to be able to

potentially penetrate infundibulum and into the hair follicle, resulting in temporarily melanin enriched

hair follicles. This is supposed to increase the light absorption by the follicular structure and improve

the effectiveness of the laser treatment; this method would specially be beneficial for clients with light

and blond hair colour (Dierickx, C. 2006).

Photo-dynamic therapy (PDT):

The principle behind PDT is that a photo-sensitizer is admitted into the targeted structure. One

important property of this photo-sensitizer should be that it becomes chemically reactive upon

exposure to the laser light, producing a type of toxic substance for example a reactive oxygen species,

as a result of the photo-chemical reaction induced by the laser light. This reactive oxygen will create a

therapeutic effect by causing positive damage to the targeted structure ( Acne scar treatment.net/acne

scarlaser treatment, 2008)

In the very recent years, introduction of a new generation of the photo-sensitizers, 5-ALA, has

opened up a variety of possible therapeutic uses including hair removal, acne vulgaris.

British Association of Dermatologists, in its guidelines for PDT, recommends that δ-Aminolevulinic

acid , to be applied topically on the skin couple of hours before treating the skin with laser light. The

unique feature of 5- ALA is that it is metabolised in the hair follicle and the pilosebaceous units by the

haem synthesis pathway to protoporphyrin IX, a natural endogenous chromophore. Therefore, 5-ALA

selectively increases the concentration of the natural endogenous chromophore within the hair follicle,

thus increasing photo-sensitivity of the targeted structure in this instance, hair follicle. Then, the skin

is radiated with an appropriate laser light with a wavelength that matches the peak absorption

coefficient of the protoporphyrin IX. The protoporphyrin IX has the highest absorption coefficient at

wavelength 405-420nm in the blue region of visible light. The second peak in the excitation spectrum

of prophyrins is the red light with wavelength 635(Morton, 2001).

The product of photo-chemical reaction of the protoprophyrin IX following the exposure to blue or

red light, is a reactive oxygen species, such as singlet oxygen or free radicals, Which will oxidize and

damage the follicular structure. The photo- dynamic therapy might be a useful approach for hair

36

removal. Because by this method photo-chemical destruction of all hair follicles is potentially

possible, regardless of the hair colour, or the stage of their growth cycle. PDT can potentially remove

even white hair (Dierickx,2006).

Intensive pulsed light sources or IPL:

Intensive pulsed light systems or IPLs are not true laser systems. Intensive pulsed light system (IPL)

is a very high intensity light source, which uses an extremely powerful flash lamp to emit a very high-

density poly chromatic pulsed light.

A flash lamp is an electric glow discharge lamp designed to produce extremely intense, incoherent

pulsed light in a broad spectrum of wavelengths (Campbell, 2008).

4.1 Physics and principles of flash lamps:

The lamp is consisted of a hermetically sealed thin tube, often made of fused quartz, which may be

straight or in different shapes including helical, “U” shape, and circular; and are filled with a noble

gas. There are two electrodes, one at each end of the tube, which are made of tungsten (because has

the highest melting point of any metal), and carry electrical current to the gas. A high voltage power

source is necessary to energize the gaz. A highly charged capacitor usually is used for this purpose to

allow delivery of very high electrical current in a very high speed when the lamp is triggered. The gas

used has a extremely high resistance to electrical current and will not conduct the discharged electrical

energy. As the result of the gas, the electrical energy will excite the gas up to highly excited higher

energy level ionized state. Once large number of the gas atoms is ionized, magnetic attraction pulls

the ions towards the opposite electrode and a spark will form between the ions and the electrodes,

which will propagate along the lamp, allowing the full ampere load from the capacitor to conduct

through the lamp. This sudden surge of amperes, heats up the gas very quickly to a plasma state,

where the electrical resistance becomes very low. So the electrical current will keep flowing between

two electrode, heating more and more of the gas atoms into ionized plasma state. As the excited

higher energy ionized atoms recombine with their lost electrons, they immediately fall beck into lower

energy state, releasing photons as they do so. (en.wikipedia.org, 2008)

37

xenon is most commonly used in the flash lamp devices, because of the brilliant, very bright and the

broad spectrum of light that it emits when excited; also for its high efficiency. Xenon can convert

nearly 50% of the input electrical energy into light (cut-tec.co.uk, 2008).

Picture 16- a basic xenon light

(en.wikipedia.org, 2008)

4.2 IPL verses laser

The light emitted from a flash lamp differs from the laser light in three ways:

The light from flash lamp is incoherent, which means its electromagnetic waves are not in

phase with each other. Each wave travels in a different phase and when they meet they will

interfere with one another. But laser light is coherent, and all its waves are in phase with one

another (Campbell, 2008).

The light from flash lamp is diverging and non-collimated. It propagates into space in every

spatial direction, and starts to diverge as soon as it leaves the light source. Nevertheless, the

laser light is collimated and non-diverging. Laser light dose not diverge noticeably and travels

in a focused narrow beam (Johansson, 1995).

The light from a flash lamp is polychromatic. Flash lamp emits every wavelength within the

visible light spectrum, and a little to the band of infrared radiation. In contrast, laser light is

monochromatic, and its entire waves have the same wavelength. In other word, laser only

emits light with a one specific wavelength (hair laser removal.co.uk, 2008)

The intensive pulsed light devices, like lasers, can be designed and made to have different of power

from extremely powerful to low intensity devices.

Intensive pulse light sources, like lasers, have many different industrial, commercial, medical, and

clinical applications.

38

4.3 History:

the xenon flash lamps, first developed as an energy source to optically pump the active medium in the

solid-state laser systems. Soon, it was being used independently with direct application of its energy

for performing a wide variety of different tasks in many different fields (scool-wikipedia.org, 2008/9).

As with lasers, flash lamps application for medical and clinical purposes started in the 1960s. During

the latter part of the 1960s, some published data emerged on treating eye and skin disorders using IPL

from flash lamp sources (intense pulsed light review.com, 2008).

In the early 1970s, some early attempts were made to deliver the xenon flash lamp energy via fibre-

optic filament, to be used as a mean of permanent hair removal. However, the results have not been

demonstrated to be permanent (hair laser removal.co.uk, 2008)

In 1976, Muhlbauer et al. first described the photo-thermal coagulation of capillary hemangiomas and

port-wine stains by means of polychromatic infrared light.[cite] however, in the 70s and 80s, there

were only a few articles about treating vascular malformations and tattoos with polychromatic, non-

coherent light (Raulin, C. 2002).

In the 1990, Goldman and Eckhouse began developing new high-intensity flash lamps for treating

vascular anomalies of the skin (hair laser removal.co.uk, 2008).

.In the 1994, the first flash lamp was cleared by FDA for use in treatment of vascular lesions. And

soon after, the first market-ready system that was based on IPL technology, called PhotoDerm VL

(Lumenis Ltd, Yorkneam, Israel) became available to public(Raulin, C. 2002).

The same year, one study noted hair loss as a side effect of vascular lesion treatment with IPL. Other

papers indicated the same result and reported hair loss as side effect of the IPL treatments, with some

of these papers the studies’ subjects being treatment of leg veins and telangiectasias. These reports

promoted one manufacturer to apply for and receive FDA clearance for hair removal in 1997. In 2000,

FDA began allowing some brands to claim permanent hair reduction in most skin types. The darkest

skin type is not included (hairlaserremoval.co.uk, 2008).

Last eight years, has witness significant series of further developments, inventions, discoveries, and

breakthroughs in both IPL technology and nature of skin-light interaction. As a result the spectrum of

possible indications, treatment options, and the levels of treatments efficiency has increased greatly.

39

4.4 IPL biophysical interactions and applications:

Today clinical IPL systems, are high intensity pulsed light sources, which emit a broad spectrum of

non-coherent, polychromatic light with wavelengths from 400nm to 1200nm. By applying different

cut-off filters on the light source, the specific parts of the shorter wavelengths, below the indicated

filter, can be filtered out. So that only wavelengths longer than the indicated filter can be emitted from

the device applicator. By using this method, the machine can be customized to selectively deliver the

desired wavelength (Dierickx, 2006).

The most commonly used cut –off filters are 515, 550, 560, 570, 590, 615, 640, 645, 695, and 755nm.

Alteration and adjustment of the spectral range used during IPL treatments, will permit the

modification of the depth of light penetration to match the target structure, the target size, and the

depth of the target location within the skin. In addition, it allows selective delivery of particular

wavelength to match the peak absorption coefficient of the selected target (Raulin & Greve &

Hortensia, 2002).

Possibility of adjusting the wavelength allows the therapist to select the treatment wavelength

according to the individual client’s skin type.

In the new versions of the IPL devices, the pulse duration is adjustable sometimes from 0.5 ms up to

25ms, to accommodate for different sizes of the different targets. The maximum fluence applied by

different IPL systems varies greatly from 20-90 J/cm2. Fluence of the most new IPL systems can be

adjusted as well from as little as 2-3J/cm2 up to the maximum fluence of the system, and can be

selected depending on the treatment, individual clients, and other parameter setting Raulin & Greve &

Hortensia, 2002).

.The size of the IPLs applicator head, generally referred to as spot size, plays an important role in the

depth of penetration of the light into skin. The larger spot size, improve the depth of light penetration

into skin, as they diminish the scattering of the light. Because skin surface is not a completely flat, the

scattering rate is increased with smaller, more focused beam ( Lepselter & Elman, 2003).

So larger spot size facilitate better penetration rate of the light, as well as reducing the treatment time.

The spot size varies between different IPL systems from 50-480mm2. Some IPL systems are devised

with different spot size to accommodate for different treatment areas Raulin & Greve & Hortensia,

2002).

Furthermore, a cool coupling gel is usually used on the skin with most IPL systems, to permit a good

optical coupling of the light and the client’s skin, improve the light penetration, reduce light

40

scattering, allow the better transferring of the heat from epidermis into the cool gel, and to prevent

skin from burning (Campbell, 2008).

Generally, the bio-optical effects of intense pulsed light with the tissue, is very similar to ones of

laser, and the same principles will apply. Mechanism of treatment with IPL , like laser, is Anderson

and Parrish concept of selective photo-thermolysis.

The new version IPL systems are equipped with a software, which guide the operator on the installed

digital screen, in choosing and setting the most suitable treatment parameters depending on the

clients’ skin type, colour, hair, and the treatment being performed (Dierickx, 2006).

In short the aforementioned properties of the IPL systems, allow a great deal of versatility in selecting

the individual treatment parameter according to the type of treatment; the treatment area; and the

selected target type, size and depth within skin. It also permits the modification of the parameters to

adapt to the different skin types and indications.

Different researches and clinical studies have concluded, “that high intensity flash lamp systems are a

successful and a non-invasive means of treatment; they provide a viable alternative to laser systems

and conventional therapeutic options when it comes to treating a series of the indications. IPL

technology has particularly proven its worth in the medical treatment of therapy-resistance port-wine

stains and venous malformations.” (Raulin, C & Greve, B, 2002).

Various published papers and documented clinical studies, have demonstrated high level of

effectiveness in numerous treatment options, along with low rate of adverse side effects, especially in

the area of aesthetic medicine and in cosmetic indications such as hypertrichosis, hirsutism,

telangiectasias, hemangiomas, poikiloderm of civatte, non-ablative skin rejuvenation (Raulin & Greve

& Hortensia, 2002).

.IPL systems have several distinct advantage over laser systems, mainly relating to IPL versatility in

permitting the choice of different wavelengths, penetration depth, pulse duration, number of pulses,

and energy fluence , therefore allowing different indication to be treated using the same device. The

other advantage of the IPL systems is flexibility to making the adjustments of different parameters

possible to adapt to individual patient’s characteristics and requirements.

Furthermore, they are more cost effective to run, and less expensive to purchase. They generally have

a larger spot size, which increases the speed of the treatment (Hair laser remvoal.co.uk, 2008).

However, because of the wide spectrum of potential combination of wavelengths, pulse width, pulse

fluence, number of pulses, the off time duration, and energy fluence, high level of knowledge about

the physics and principles of the photo-therapy, deep understanding of biological light-tissue

41

interaction, and a great deal of experience is essential when operating IPL systems. Also proper,

careful patient selection and critical diagnosis are important factors at keeping the incidents of adverse

effects of the treatment, (such as severe erythema, epidermal burns, superficial crusting, temporary or

permanent scarring, hyper or hypo pigmentation, or ineffective treatments,..) to minimum.

5.Various Pulsed light or VPL system:

Various pulsed light system, is the third generation of the skin treatment and hair removal systems.

This system, with the trade name of Ultra VPL, is the newest form of intensive pulsed light

technology, designed and invented by Energist ( Energist international Ltd, Swansea, UK), which has

been developed another step and has been advanced yet further from its predecessor IPL systems

(Ultra-vpl.com, 2008).

Ultra VPL, changes the way we treat different chromophores in the selected targets within the skin, by

changing the way the pulses of the intense light are emitted.

Ultra VPL machine is differs from and has advantage over conventional IPL systems in many ways.

Firstly, it has a state-of-the-art design, and it has been manufactured and produced to the highest of

standards. All of the different components utilise the most advanced technology available today, and

are from the highest quality (Campbell, 2008).

The second advantage is the energy available from the system. Ultra VPL is one of the most powerful

intense pulsed light sources currently available in the market (Ultra-vpl.com, 2008).

However, the main advantage of the Ultra VPL system over other IPL systems, is that Ultra VPL

delivers an adjustable sequence of discrete rapid micro pulses in each shot of intense light it emits.

The fluence of each shot, the number of micro pulses, their length, or duration, and most importantly

the length of delay between micro pulses can be adjusted. therefore, it allows for creating optimal

treatment protocols for a wide variety of skin types and conditions; broad range of indications, and

ensures safe, effective, and fast treatments (Campbell, 2008).

In another word, the conventional IPL systems, the energy fluence of each shot is delivered upon skin,

with one or two pulses of intense light. The pulse or the pulses have a fixed length (on time) and a

fixed time gap between the two pulses (off time). The light energy is delivered to skin during the

emission time of the pulse (or during the added emission time of the two pulses) or on time, and the

selected target along with the skin cool off during the fixed time gap between two pulses.

42

However, the disadvantages of this type of pulse structures are that the fixed on time and off time

offers little versatility, and does not allow the energy delivery and the treatment structure to be

adjusted to adapt with different types of skin or various indications.

On the other hand, deposition of the total energy fluence to the skin during one or two pulse often

create a very rapid build up of the heat in the target and the most importantly in the epidermis. As the

result, the temperature of the target structure and the epidermis will rise very sharply to a very high

temperature, above the damage threshold of epidermis and the tissues surrounding the target. This can

cause undesired damage to the surrounding tissues and even worse the epidermis, increasing the risk

of adverse effects such as skin burn, blisters, scaring, and hyper or hypo pigmentations ( Campbell,

2008).

The Ultra VPL, operates differently. In simple terms, it breaks down the exposure time of the light

pulse, into a series of very short equal micro pulses. And it delivers the total energy fluence during the

total on time of these micro pulses. Ultra VPL also breaks down the off-time into mini off-time

intervals separating the mini pulses (ultra-vpl.com, 2008).

For example, a typical IPL system delivers the total fluence of 30J/cm2 during a long pulse with the

on-time of 30millisecons, or during the on-time of two 15ms pulses, with a gap of 12ms in between

the two. The Ultra VPL will deliver the same total fluence with a different pulse structure.

The VPL, will break the 30ms on-time down to numbers of mini on-times, i.e. to 6 micro pulses with

5ms on-time for each micro pulse. The 30 J/cm2 fluence will be delivered into skin equally by these

micro pulses. Therefore, during the length of each micro pulse 5J/cm2 energy will be deposited into

skin. There will be four micro gaps of 3ms as the off time between the micro- pulses.

43

Picture 17- (Campbell, K. 2008)

This is called a pulse train. We represent a pulse train and its different parameters as followed:

Pulse train: F= X.Y.Z

Where X is the number of pulses, Y is the length of each pulse/on-time, and Z is the off time

(Campbell, 2008).

Therefore, to represent the pulse structure or pulse train of the above example we will write:

30=6.5.3

Thus the total length of each shot or the total train time can be calculated as followed:

(total pulse train time/length of each shot) = [(number of pulses) × (on time)] + [(number of pulses -1)

× (off-time)]

So:

T = (X ×Y) + [(X− 1) × Z] (Campbell, 2008)

44

Pulse Train

y

z

T

Total = x

Pulse TrainPulse Train

y

z

T

Total = x

Picture 18- pulse train (Campbell, K.2008)

One of the most important concepts of Ultra VPL system, is that the number of these pulses, the on-

time and the off-time are variable parameters, and should be selected for each individual treatment

according to the selected target, skin type, the treatment type, and desired outcome of that treatment.

Campbell (2008) states that Ultra VPL offers:

Three different pulse durations or on-times of 3, 5, and 7 milliseconds.

The number of micro-pulses can be between 2 to 15 pulses, giving 14 different options

The off-time can be selected from 1ms to 20 ms, giving 20 options

Therefore, altogether the Ultra VPL offers (14 × 20 × 3 =840) possible pulse structures.

And the total time of the longest pulse train possible or the longest shot is 385ms and the total time of

the shortest possible pulse train or the shortest shot is 7ms. Therefore the total pulse time or the length

of each shot can vary between 7ms – 385ms

5.1The principle of micro pulse structure:

Almost all of the photo based treatments, including laser and IPL/VPL assisted treatments, work with

photo-thermal mechanisms. So the objective of all of them is to deliver the sufficient light energy into

45

a selected target in order to raise the temperature of the target to critical point (which is the tissue

damage threshold), while sparing the surrounding tissue.

The tissue thermal damage threshold is usually about 70 ℃. Therefore, for a successful treatment we

need to ensure we raise the temperature of the selected target to about 70℃; at the same time, we

must ensure that the temperature of surrounding tissues and most importantly epidermis is kept within

a safe range to prevent any adverse effects and epidermal damage. The safe temperature for most

tissues usually is below 45-50℃ (Anderson & Altshuler, 2001).

All the different wavelengths in the visible light part of the spectrum, plus over lapping into the near

infrared and ultra violet parts (wavelengths between 350 – 1100nm), are heavily absorbed by two

natural chromophores melanin and haemoglobin.

Looking at the picture 14, we can see that haemoglobin has high absorption coefficient in the blue-

green and the yellow region of the spectrum. Although, melanin is the domain absorber of the red and

near infrared lights, but in order for a beam of light to reach the selected target within the structure, it

has to pass through the epidermis, where the epidermal melanin is a competing site for the light

absorption. Therefore, it is impossible to heat the selected target up, without heating the epidermis

too.

However, with using the principle of selective photo-thermolysis and the difference between thermal

relaxation times (T R) of the target and epidermis’ and utilising the micro-pulse structure of VPL; we

are able to control the temperature of the epidermis and keep it below a safe level throughout the

treatment.

As mentioned previously, the thermal relaxation time of a structure increases in line with the square of

its dimension. Thus, we can conclude that the smaller structures have much shorter T R than larger

structures. The melanin granules within the epidermis and melanocyte cells, have a very short thermal

relaxation time ( 1-10 ms), while the target structure, be it vascular lesion, hair follicle, ...), is a much

larger and denser structure. Therefore, the thermal relaxation time of the target will be much longer

the follicular T Ris 40-100ms ( Sadnick & Weiss, 2000).

As soon as we start radiating the target structure, the temperature in the target and the epidermis start

to rise. By the end of the first micro-pulse, the temperature in both the target and the epidermis will

rise for several degrees. However, if we choose the micro-pulse duration in a way, so it is longer than

epidermis thermal relaxation time [Y > (1-10ms)], but it is shorter than the targets thermal relaxation

time, then we make sure the temperature increase in the epidermis is much less than the target tissue.

46

As soon as the irradiation stops, and the off-time starts, the temperature in both the target and the

epidermis starts to fall down, but it happens much faster in the epidermis, than in the target. If we

select the off-time length, so it is longer than epidermis thermal relaxation time, but much shorter than

the target thermal relaxation time, then by the end of the off-time, the epidermis will have lost up to

half of its temperature and would have cooled down significantly.

In contrast, the target will have only lost a fraction of its temperature, usually less than 10%, so the

heat will be confined within the target (ultra-vpl.com, 2008).

. Picture 19- comparison of increased skin temperature in IPL and VPL

(Campbell, 2008)

During the second micro-pulse starts, the temperature of both epidermis and target will rise again, but

the rise will be more than epidermis. Besides, during the second off-time, the epidermis will cool

down again, while the target will have lost 10% of its total temperature by the end of the second off-

time, and the pattern will repeat.

Within the course of a few micro-pulses, the temperature within the target will build up to a high

level, while the epidermis temperature will be only slightly higher than its original temperature, and

certainly below a safe limit.

47

Time Time

Temperature

Temperature

Hair

Skin

Optimum

Safe

VLP system, therefore, enable us to raise the target temperature to the thermal damage threshold, in a

gradual process, while keeping the dermis in a safe thermal zone. The gradual heating of the target

ensures its sufficient thermal damage, also prevents undue pain to the client, hyper or hypo-

pigmentation usually caused by sudden rise in the epidermis and the tissue surrounding the target.

Due to the Ultra VPL micro-pulsing structure, the overall temperature rise of epidermis is not high.

Energist suggests that this eliminates the need for pre-cooling the skin prior to irradiation.

On the other hand, the main effect of pre-cooling is that the skin starts from a lower base line

temperature, to protect the skin more. However, pre –cooling of the epidermis, will also reduce the

base line temperature of the target structure within the skin to some extent. Thus we will need to

deliver more fluency to achieve the same level of thermal damage, which will be more of a risk for

epidermis (ultra-vpl.com, 2008).

Ultra VLP, instead, utilise a direct water – cooling mechanism, with applying a special optical –

coupling gel which has a high percentage of water content. Another advantage of the direct water –

cooling is that it keeps the applicator head cool, and prevents it from getting hot during the treatment.

This way the starting temperature of the skin surface is controlled even during long treatment

procedures (ultra-vpl.com, 2008).

In addition, it is advisable to avoid pre – cooling of the skin when treating vascular lesions as well as

skin rejuvenation treatments. As the pre – cooling causes the facial superficial blood vessels to

constrict, reducing the volume of the blood flowing in the target vessels, as the result decreasing the

absorption coefficient of the vessels and affecting the efficiency of the treatment (ultra-vpl.com,

2008).

48

Picture 20 ( Ultra-vpl.com, 2008)

Setting the treatment parameters:

As discussed earlier, the Ultra VPL system utilises a variable micro – pulsing mechanism, which is

very versatile and enables the therapist to modify the irradiation structure to adapt to individual

treatments and clients, by selecting the appropriate parameters. The most important parameters, which

determine the level of treatment efficiency, include wavelength, on – time, off – time, number of

pulses, and the energy fluency.

The wavelength should be chosen depending on which type of chromophores are present within the

selected target structure.

The Ultra VPL machine, produces radiations between 400 – 1200nm wavelength. The system devises

two cut – off filters. These filters will allow us to choose a suitable range of wavelengths, to be

emitted from the light source, while filtering out any shorter wavelengths below our selected range.

The spectrum of the wavelength we choose, should match the absorption coefficient of the

chromophores within the target. The system includes a red cut – off filter, which cuts out any

wavelengths shorter than 610nm. The red applicator emits red light with wavelengths between 610 –

950nm. Any wavelengths above this are negligible, due to the filtering technology and the water –

cooling mechanism, which intrinsically filters out any longer IR wavelength – the longer IR

wavelengths are heavily absorbed by water (Ultra-vpl.com, 2008).

49

The domain chromophore for red and near infrared lights (610 – 950nm) is melanin. Therefore, the

red filter should be used for hair removal treatments.

The other cut – off filter or yellow applicator, filters out any wavelengths shorter than 530nm, only

allowing wavelengths between 530 – 950nm to be emitted.

The peak absorption coefficient of haemoglobin lies within this region of the spectrum. Therefore, the

yellow applicator should be chosen for treatment of vascular lesions.

Another important factor, which affects the choice of wavelength, is the required depth of penetration.

The melanin absorbs strongly all the wavelengths between 530 – 950nm. In fact, the absorption

coefficient of the melanin decreases towards the longer wavelength. As we can see in the table [],

melanin absorbs the 530nm wavelength more than the wavelength 750nm.

However, we do not use the 530nm wavelengths for targeting melanin – hair shafts, because they

cannot penetrate into skin deeply enough. The hair matrix is lying deep within bottom layers of

dermis. Therefore, we need a wavelength, which not only is absorbed primary by melanin, but also is

able to penetrate deep into dermal layers, like red light.

However, when treating a pigmented lesion, we need a wavelength absorbed strongly by melanin,

which does not penetrate deeply into dermis; instead, it deposits all of its energy into epidermal layer.

Thus, the yellow applicator will be the right choice.

Another important parameter is the pulses durations or on – time. During this time, we irradiate the

target in order to increase its temperature. So the aim of the on – time duration is to deliver enough

energy to the target, in order to increase its temperature effectively, while confining the heat within

the target structure (Campbell, 2008).

Larger structures take much longer to heat up than smaller objects. Therefore we choose the on –

time, depending on the size of the target. An optimal duration is one, which is long enough to allow

the effective heating of the target, but at the same time is noticeably shorter than the target thermal

relaxation time, to ensure the confinement of the heat within the target.

There is a choice of three wavelengths with this system: 3, 5, and 7ms. Therefore, we choose the3ms

for the small targets, 5ms for medium sized targets, and 7ms for large targets (Campbell, 2008).

The off – time duration can be set between 1 – 2ms. The principle of off – time is to let the epidermis

to cool down. So the appropriate setting will depend on the client’s skin. Generally, darker skin

absorbs a greater percentage of the incident light, due to concentration of the melanin within the

epidermis. Thus, the temperature in this type of skin will rise more than fair skin. The higher

temperature means it takes longer for this skin to cool down.

50

The number of micro –pulses is a very important factor, which will affect the efficiency of the

treatment. The number of the pulses ultimately determines the total exposure time.

As we know

Pd = Ft

As shown in above equation, for a given fluence, the longer the energy transfer time, the less the

power and density of the treatment.

So, if the number of the pulses is too great, it means that; the total time it takes for us to transfer the

energy on to the target, will be too long. This will allow the target to cool down as it heats up. as the

result, the sufficient temperature within the target will not be achieved, making the treatment less

effective.

However, if we do not select enough number of pulses, then the total treatment time will be too short.

Therefore, the total energy will be transferred into the target, over a very short period. This causes the

target temperature, also the epidermis temperature to rise rapidly to a very high level, causing damage

to the surrounding tissue, and epidermis.

when choosing the number of pulses, we have to carefully consider the client’s skin type and

tolerance; also the required power in order for the treatment to be effective.

6. Various photo– skin therapy treatments:

As the result of new discoveries about the biological effects of light radiation on the skin tissues, and

the further improvements of laser technology and light source systems; over the past decade,

numerous light-based therapeutic options, particularly in the field of beauty, have become available.

In the last few years specially, there has been a great interest in the development of new non-invasive,

non-ablative methods to effectively treat and improve the appearance of different problematic skin

conditions. None of these methods can match the successful results achieved on a variety of

indications using laser systems and intense light sources.

Today, broad range of cutaneous conditions are safely and effectively treated or improved with

utilising light technology including;

Hair removal

51

Benign pigmented lesions

Benign vascular lesions

Non-ablative skin rejuvenation

Acne vulgaris

(Campbell, 2008)

6.1 Hair removal:

The mechanism of light assisted epilation, the same as majority of other laser treatments, is photo-

thermal mechanism. In this mechanism, a natural or artificial chromophore is present in the body, in

the selected treatment target, which absorbs the light more strongly than surrounding tissues and heats

up (Dierickx, 2006).

The laser hair removal focuses on the natural chromophore melanin, which is present in the hair shaft

and follicular structure (Akita & Anderson, 2004).

when we irradiate the treatment area with either monochromatic or broad band EMR (mainly visible

light or near IR), at a wavelength preferentially absorbed by melanin, then the incident light energy

will be mainly absorbed by the melanin within the hair shaft and follicular structure, and will convert

to heat, causing thermal damage to hair shaft and follicular structure. This way we can induce a

selective thermal damage to the hair follicle.

A hair follicle consists of three regions: the infundibulum, isthmus, and the hair bulb. The inferior

segment of the hair follicle lies below the arrector pilli muscle insertion, and it includes the hair bulb

and dermal pilli (Campbell, 2008).

The hair bulb is made up of germinative matrix cells along with interspersed melanocytes.

The dermal papilla is located at the base of hair bulb, and it is made of dermal sheath cells. It has a

rich blood supply, which supply the nourishment to produce new hair.

The bulge is located approximately one third of the way from the skin surface to the bulb, and

contains pluripotential stem cells (Lepselter & Elman, 2003).

52

Picture 21 – follicular structure (Campbell, 2008)

These three area, the matrix cells in the bulb, dermal papilla, and the outer root sheath and dermal

sheath in the bulge, are the hair growth centres.

For an effective hair removal, we should create a light induced thermal damage to these growth areas

(Lepselter, J & Elman, M. 2004)

Another point to consider for effective hair removal is the hair growth cycle.

Human hair has a life and growth cycle. This cycle is consisted of three stages: anagen, catagen,

talogen.

The total length of hair cycle, also the length of each stage varies widely depending on: anatomic

location, age, gender, hormones, season, and genetic.

Hair follicles undergo profound anatomic and metabolic changes between the growth stages, which

can affect their sensitivity to photo- thermolysis (Lin & Dierickx, 1998).

Anagen is the active growth stage of the hair. In this stage, actively growing matrix cells are heavily

pigmented, with high melanin concentration as the activity of the melonocytes is at its peak. During

the anagen the hair shaft is fully pigmented along its entire length. The dermal papilla and hair bulb

are deep within the dermis (at their maximum depth) and well connected. Therefore, the hair

absorption coefficient is high at this stage. In addition, the heat created within the hair shaft and bulb

is transferred to the dermal papilla more effectively (Lin & Dierickx, 1998).

53

.

When growth stage ends, the hair enters catagen. Catagen is a relatively brief transitional stage.

During this stage melanocyte activity and hair growth suddenly cease. The hair shaft becomes de-

pigmgmented, at least up to skin surface. Therefore, is has a much lower absorption coefficient from

this stage to the end of its cycle (Lin & Dierickx, 1998).

.

Besides, the base of the hair follicle moves upward to the resting stage, disconnecting itself from the

dermal papilla.

And the hair enters talogen. As the hair enters talogen, the melanin production is completely absent,

and the follicular stem cells are dormant.

So we can conclude that causing thermal damage to the follicle, only is effective during anagen stage.

Therefore, successful permanent laser hair removal or reduction, can only be achieved during anagen

stage. The clinical studies have proven this theory too (Lin, D & Dierickx, C & Manuskiatti, W.

1998).

a) Anagen |b) Catagen c)Talogen

Picture 22- hair growth cycle ( Dermatology Focus, 2006)

Physic and skin – optic of hair removal:

As discussed earlier, the mechanism of laser hair removal is selective photo-thermolysis (SP).

Our targeted chromophores are melanin present in the hair shaft. The treatment area is irradiated with

monochromatic laser or broadband intense pulsed light, with a selected wavelength primarily

absorbed by the melanin( Akita & Anderson, 2004).

As the melanin absorbs the light energy, it will heat up. This heat then will heat the adjacent follicular

structure by the thermal diffusion. The heat should be the right level to induce a thermal damage to

54

the hair and follicular structure, while sparing other skin structures. This way we have produced a

selective photo-thermal damage or selective photo-thermolysis.

However, effective laser hair removal is a multi-factorial process, which involves complex photo-

thermal reactions via the dermis, epidermis, matrix, hair shaft, and the follicle with the aim to induce a

sufficient thermal damage to the hair growth sites, while preserving the epidermis (Lepselter &

Elman, 2003).

Therefore, the efficient and successful irradiation of hair follicle by a light source, involves various

laser and tissue parameter. Lepselter and Elman (2003) have listed the most important laser

parameters as: wavelength, energy fluency, power density, irradiation time, repetition, spot size,

shape of the EMR pulses.

The main tissue parameters include absorption coefficient, scattering coefficient, depth, target size,

thermal diffusivity, and heat capacity.

We should select these parameters to induce adequate thermal damage, not only to the hair shaft and

matrix, but to the other hair growth sites, dermal papilla and bulge. Meanwhile, we should protect the

epidermis from overheating to prevent scarring or dyspigmentation (Altshuler & Anderson, 2001).

The hair root and bulb during anagen stage are located deep into dermal layer, on average 4-5mm

from the skin surface. Therefore, we need to select our parameters in a way to ensure adequate

penetration of the light into the skin.

The depth of penetration depends on different factors. Wavelength affects the depth of penetration

directly. Generally, longer wavelengths penetrate deeper into skin therefore; there will be greater ratio

of dermis to epidermis energy deposit.

So we need to choose a wave length that is absorbed mainly by melanin and can penetrate deep into

dermis. Melanin absorbs all the wavelengths between 350-1100nm very well. Around red to near IR

light most of the light energy is absorbed by melanin, this wavelengths can also penetrate deep into

dermis too. Although the absorption coefficient of the melanin decreases by the longer wavelengths,

and is higher toward the blue/violet end of spectrum than the red end, but shorter wavelengths cannot

penetrate deep into skin. So very low absorption coefficients by other competing chromophores , and

good penetration depth at red or near IR wavelength make them a good choice for hair removal.

Other than wavelength, spot size affects the depth of penetration too. Ideally, spot size should be as

large as possible to reduce the scattering of the light. When light is applied to the skin in a small

beam, as the epidermis is a irregular surface, it scatters the beam a great deal. The scattering of

photons diffuses the beam rapidly. The fluence decays very quickly as a function of depth. as the

55

result, most of the energy is dissipated in radial direction (outwards) and it cannot reach the hair bulb.

with a large spot size, light penetration is more efficient since the “source” of the photons has almost

planar geometry(Lepselter, J & Elman, M. 2003).

The fluency also affects the amount of light energy that reaches the hair bulb and is deposited into it.

As only, a percentage of the beam energy reaches the bulb. “for normally incident radiation, the

reflectance of an incident beam from normal skin is always between 4% and 7% over the entire

spectrum from 250 – 3000 nm, for both white and black skin(Anderson, R, R. 1981).

Therefore, only 93% - 96% of the light that is not reflected can potentially be absorbed to any layer

within skin structure. Some more percentage of the light on its way to the bulb through the different

skin layer, will be absorbed by epidermal melanin. In addition, some of the photons will be scatter

further (back scattering) by different skin layers. In human skin, only about 15%-20% of incident light

at 700nm penetrates to a depth of 3mm ( Lepselter, J &Elman, M. 2003).

The penetration depth can vary in different individual’s skin as well, as the result of different tissue

parameters. The epidermal or corneal transmittance spectra are compositely determined by absorption

by major epidermal pigment substances. Variations in concentration, distribution, or amount of these

chromophores, and in epidermal thickness, largely determine individual and anatomic variations in

epidermal spectral transmission(Anderson, R, R. 1981).

Therefore, we can conclude that for the same wavelength and fluency, the penetration depth will be

less in darker thicker skin types. This reconfirms the need to choose longer wavelengths for darker

skin types. Because not only the greater ratio of dermis to epidermis energy deposition in longer

wavelengths, make it safer for the dark skin types; but also the reduced absorption coefficient by

melanin at longer wavelengths enables the light to bypass better through the barrier of the

concentrated epidermal pigments. Therefore reaching the bulb area better.

Another point to remember is that the hair density at treatment site, will affect the penetration depth.

Denser present of hair, results in more of the light energy to be absorbed with the melanin-rich hair

shafts, therefore reducing the penetration depth. As the clients return for further treatments, decrease

in hair density means deeper penetration, so deeper setting follicles are more likely to be treated in

subsequent treatment than the initial treatments (Lin & Dierickx, 1998).

The other very important treatment parameter, which has been a lot of debates over it over the years,

is the pulse duration or the exposure time.

Frenz (2002) explains when any tissue is irradiated, the biological reactions occurring within the

tissue depends on parameters of exposure time and radiation fluency:

56

If extremely large amount of energy is radiated into tissue in a extremely short time it will

create a mechanical shock wave within the tissue, resulting in the exposure and fragmentation

of tissue. Q- switching lasers used for tattoo removal use this mechanism

If a large amount of energy is delivered into tissue very quickly it will rise the tissue

temperature very rapidly and evaporates the tissue resulting in tissue cauterization or ablation.

If the energy is delivered in to skin over moderate length of time, it will rise the tissue

temperature to the point of irreversible damage and de- natures the tissue resulting in tissue

coagulation

If we deliver the energy over a long period, it creates a reversible damage.

For hair removal, we need to coagulate the follicular structure. Therefore, we should avoid the target

temperature to rise to the vaporisation level.

If we raise the hair shaft and hair bulb temperature rapidly to the vaporisation level, the absorption

coefficient of the hair bulb will drop suddenly, before it has had sufficient time to heat the other

follicular structures to thermal damage level. Furthermore, radiation will not be effective, as the hair

bulb will absorb it poorly (Lin & Anderson, 1998).

In addition, if we vaporize the hair bulb a great amount of EMR energy will be consumed for phase

transmission and destructive processes. To prevent this undesired effect we need to limit the

temperature rise in the hair bulb to below the vaporisation level. The vaporisation temperature for

melanin is around 100℃ (Lin & Anderson, 1998).

Laser hair removal usually is performed using the selective photo-thermolysis concept, suggested by

Anderson and Parrish. According to SP method in order to achieve a selective photo-thermal

destruction of the target, we must deliver sufficient energy fluency; at a wavelength mainly absorbed

by the chromophore present in the target; within a time of less or equal to the target TRT.

However later on this concept was further developed by corollary concept of thermo-kinetic

selectivity ( Sadick & Weiss, 2000).

This theory propose that longer pulse duration will allow the intra-pulse cooling of the smaller

structures more rapidly than larger structures.

So this concept is being used to prevent epidermal damage.

As we irradiate the treatment area with a wavelength at which melanin is the domain absorber, then

the melanin in the hair bulb will heat the bulb up by absorbing the light. However, the melanin present

in the epidermis, represents a competing site and will heat the surrounding epidermal cells by

absorbing the light too.

57

The thermo-kinetic selectivity suggest that if we choose a pulse duration which is shorter than hair

follicle TRT, but longer than epidermal TRT, and melanocyte TRT, then these smaller structure will

lose some of their temperature through thermal diffusion, during the pulse duration. Therefore, their

temperature will not rise as high as the larger hair follicles.

In other word, they keep losing their heat as we are giving some more heat to them.

Melanocyte TRT is about 0.1ms and the entire epidermal TRT is between 3-10ms (depending on the

skin type). The follicular TRT is between 20 – 60ms, depending on the hair thickness and colour

(Lepselter & Elman, 2003).

We can conclude if we choose the pulse duration longer than (3-10mn) but shorter than (20-60mn) we

will confine the temperature rise and thermal damage to follicle and prevent the overheating of the

epidermis.

This concept also was used to design laser devices that deliver the light in a few pulses with off-time

in between. The off-time is set using the same principle.

The off-time is longer than epidermis TRT to allow sufficient cooling of the skin, but shorter than

follicle TRT to preserve the follicle temperature and also confine the thermal damage to the follicle.

In other word, we selectively heat up the follicle during pulses, and selectively cool than the

epidermis during off time.

However, recently Anderson has further developed the original selective photo-thermolysis concept

by suggesting a new method for un-uniformly pigmented targets (Altshuler, G.B. & Anderson,

R.R. ,2001).

As we know for effective hair removal the dermal papilla, bulge area, and outer root sheath and

dermal sheath need to be thermally destructed as well as the hair bulb. However, these areas do not

contain any melanin. Therefore the only way to destruct them is through heat transmission to them

from hair bulb by thermal diffusion. Anderson refers to this type of target as un-uniformed targets

because the chromophores are not distributed throughout the target. Only a part of the target absorbs

the light.

Anderson suggests that thermal damage of these types of targets requires deposition of enough heat

energy into absorbing area and good heat exchange between absorbing area and the target outermost

parts. Heat deposition depends on absorption coefficient of the absorber and the power density of the

EMR. Heat exchange depends on the distance between the absorber and the outermost parts of the

target and on the heat transmission coefficient of tissues (Altshuler, G.B. & Anderson, R.R. ,2001).

58

As we know, the temperature for thermal damage of most soft tissues is around 70℃. Therefore

Anderson propose that for optimal result, we should make sure the temperature of the outer root

sheath reaches a maximum of 70℃ while we maintain the bulb temperature at maximum 100℃ (Altshuler, G.B. & Anderson, R.R. ,2001).

This requires that EMR power density must be limited but sufficient to heat the target to damage

temperature.

Pd= Ft

So this means in order to limit the power density, we must increase the time. In other words, we

should avoid depositing the light energy to the hair bulb too fast. We need to deliver it over a longer

period.

Lin and Anderson ( 1998) refer the time it takes the bulb to transfer enough its heat to the outer root

sheath (ORT) in order for the ORT reach 70 ℃ is, as thermal damage time (TDT) of the follicle. And

they suggest that TDT is significantly longer than follicle TRT.

However, the challenge is how to keep the hair bulb temperature in a constant level of below 100℃

and sustaining the epidermal temperature within a safe limit during the course of such a long exposure

time.

The VPL system might be the right answer for this challenge. The micro – pulse mechanisms of VPL

system alongside with its adjustable micro off - time intervals, allows the long exposure time

suggested by the new extended SP, to be broken down into a series of micro pulses. The off-time

intervals then can be adjusted in such a way that it allows the hair bulb to lose some of its heat and to

cool down a little before its temperature is raised again by the subsequent micro-pulse. In other

worlds, the hair bulb cools down as it heats up. this way it is possible to maintain the hair bulb

temperature in a constant level, just below 100℃ even throughout a very long exposure time

suggested by new Extended SP Theory.

In addition, the VPL system, facilitates the flexibility to adjust the duration of off-time intervals

according to the skin type requirements, ensuring safe epidermal temperature throughout the long

exposure time.

It can be concluded that the new Extended Theory of the Selective Photothermolysis, reinforces the

advantages of VPL system over other conventional IPL systems.

59

Benign pigmented lesions:

The principle behind the pigmentation removal is slightly different to hair removal.

A dermatologist called Goldman was the first person to experiment the effect of laser light on the skin

in 1963. during his experiments he found out that light is absorbed selectively by melanin (Scheinfeld,

2008)

In later research he found out that when working with Q-switching lasers, the damage threshold of

pigmented lesions was independent of the skin colour (Scheinfeld, N. 2008). So he concluded that

selective damage was possible at the melanosome level.

Twenty years later, Dover, demonstrated that the selective destruction of the melanosomes are pulse-

width dependant. He irradiated melanosomes by different pulsed width lasers. After examining the

irradiated melanosomes with electronic microscope, he found that the melanosomes treated with loner

pulses were not destructed, while the internal structure of the melanosomes treated with short pulses

were destructed (Scheinfeld. N, 2008).

This is consistent with the classic SP theory. As the melanosomes are tiny structures their TRT is very

small. If treated with long pulses they lose their heat by transferring into surrounding cells while

being irradiated. So their temperature will not rise to thermal damage level. It can cause damage to

surrounding tissues.

Therefore, when treating pigmentation lesions, we use the photo-mechanical mechanisms or

vaporization methods. We need to deliver the energy required to destruct the melanosomes in as little

time as possible. This will either cause an acoustic wave within the melanosomes resulting in

scattering or fragmentation, Or it will rise the melanosommes temperature so rapidly, that vaporizes

them.

As mentioned before, the melanin absorbs light in the whole range of the visible light. When treating

pigmentation we use wavelength in the yellow or green part of EMR spectrum due to increased

absorption coefficient by melanin ad shorter wavelength region of spectrum and the more superficial

effect on the skin. As pigmentations are located in epidermal layers; we need a wavelength, which

deposits all its energy in epidermal layers and is strongly absorbed by melanin. Longer wavelengths

are not used as they penetrate deep into skin. They have been found to disturb the basement of

membrane with pigmentary incontinence (Scheinfeld. N, 2008).

The second absorption peak for haemoglobin lies in at wavelength between 600-570nm. After that, it

falls sharply toward 500nm. At wavelengths around 500 nm, there is the biggest absorption difference

60

between haemoglobin and melanin. As the result, wavelengths in that region are the most commonly

used for pigmentation treatments.

However, when treating deeper setting pigmentation, longer wavelengths (630 – 1100nm) can be

successfully used. The point to remember is that with longer wavelengths the more fluency is needed

to create the same thermal effect during the same pulse width (El Rouby, 2007).

Generally, the smaller structures consume less energy for their temperature to rise than larger

structures. Therefore, although the energy fluency needed depends on the lesion size, but generally is

less than we would need for hair removal.

Scheinfeld (2008) states that the epidermal repair following pigmentation treatment, happens in three

stages. Immediately after the treatment, the pigment changes its colour. It might turn whitish,

darkened, or scatter.

In the course of the following weeks, there might be a transient hypo-pigmentation while the body is

sloughing away the killed pigmented cells. This will be followed by gradual re-pigmentation back to

the normal colour.

Benign vascular tissues:

When treating the vascular lesion, our targeted chromophores are oxyhaemoglobins in the blood.

Haemoglobin absorbs the light in a wide range of wavelengths. However, there are two peaks on the

haemoglobin’s absorption coefficient chart. The highest peak is between 420-450nm and the second

peak is 570-600nm. For laser treatment f cutaneous vascular lesions, the second peak is usually used.

Because the very short wavelengths between 420-450nm are usually absorbed by the top skin layers

and will not penetrate into skin deep enough to be able to target the vessels (Goldberg, 2008).

The optimal vessel treatment can be achieved by denaturing and coagulating endothelium, the

innermost layer of the vessels. The principle used to treat vascular lesion is the Extended Selective

Photo-thermolysis similar to hair removal ( Lin & Anderson, 1998).

Lin and Anderson (1998) indicate that the haemoglobin within the blood absorbs the light and heats

up. Then it transfers its heat to the surrounding tissues, which is the endothelium. They suggest we

therefore, need to allow enough time for the blood to transfer its heat to the vessel wall. But we have

to remember that the endothelium is smaller structure in comparison to the hair follicle, so it heats up

quicker and has shorter TRT.

61

As result, we need to deliver medium energy in short pulses. The energy fluency should be set

depending on the depth and size of the lesion. The pulse width is set depending on the lesion size and

depth. If a client has deep setting lesions and superficial setting lesions, we can treat the superficial

first using wavelength 570nm, then treat the deeper ones in subsequent treatments using 600nm and

more energy.

Health and safety:

There are many different hazards involved when operating a laser or intensive pulsed light system.

Therefore, it is important that we are aware of these and protect the health and safety of our clients,

our colleagues, and ourselves.

Campbell (2008) divides the different laser hazards into following categories:

Biological hazards

Electrical hazards

Mechanical hazards

Fire hazards

Fumes

Biological hazards

Skin:

Biological hazards of laser can include skin burn, damage to skin and underlying tissues damage as

the result of accidental unprotected exposure. The extent and type of these damage depends on the

energy, wavelength, power density of laser (Campbell, 2008).

But in general the damages laser can cause to skin, can be divided to: photo-thermal damages, photo-

chemicals, photo-mechanicals

If skin is exposed to low level of laser energy for a long period, it causes photo-chemical damage such

as premature aging or cancer by excessive and chronic exposure to UV radiation

(geocities.com/laser_biological_hazards_skin, 2008).

If a medium energy laser light radiates to skin even for a very short time, it causes photo-thermal

damage like skin burn, tissue coagulation, cauterization.

62

If a high power laser light hits the skin even for small fraction of a second, it cause severe photo-

mechanical damage to skin and underlying structures, like acoustic shock to tissue, tissue rupture,...

(geocities.com/laser_biological_hazards_skin, 2008).

Eyes:

Laser irradiation of the eye can causes damage to the cornea, lens, or retina depending on the

wavelength of the light, the energy level, pulse duration and the absorption characteristics of the

ocular tissue(geocities.com/laser_biological_hazards_skin, 2008).

.The part of the eye that will be damaged, directly depends on the wavelength.

UV light: most of the radiation is absorbed in the lens and usually the effects are delayed and may not

occur for a long time. I.e. cataracts

Visible light and NIR: most of these lights is absorbed by the retina and can cause flash blindness,

retinal burns, and lesions.

Far infrared: most of the radiation is transmitted to cornea and can cause corneal burns

(geocities.com/laser_biological_hazards_skin, 2008).

We have to bear in mind that laser retinal injury can be severe because of the focal magnification

(optical gain) of the eye, which is approximately 100,000 times. This means that an irradiation of 1

W/cm2if entering the eye will be effectively increased to 100 W/cm2when it reaches the

retina(geocities.com/laser_biological_hazards_skin, 2008).

The pulse duration also effects the potential for eye injury. Pulses less than 1ms in duration focused

on the retina, can cause an acoustical transient, resulting in substantial damage and bleeding in

addition to the expected thermal injury (geocities.com/laser_biological_hazards_skin, 2008).

The ANSI Z136.1 standard, defines the Maximum Permissible Exposure ( MPE) that the eye can

receive without expecting an injury.

The first rule of laser safety is : never under any circumstances look into ant laser beam, and

prevent the laser beam and beam reflections from entering the eyes of ourselves or our clients.

Electrical hazards:

63

Laser uses large power electricity supplies, therefore there is a potential for different electrical

injuries. The main electrical hazard is electrical shock. Electrical shock can happen if we work with a

laser device, which has not been properly grounded or discharged, not following the OSHA lock-out

standards, lack of knowledge about the device, hidden signs, uncovered or improperly insulated

electrical terminals and wires (geocities.com/laser_biological_hazards_skin, 2008).

In order to prevent electrical shock, we must not remove the earth wire, panels, or the hand piece

cover. We must also remember that even when the mains supply is turned off, high voltages may

remain in some components such as capacitors ( Campbell, 2008).

.

Mechanical hazards:

Trailing cables, incorrect cable connection, placing the device near the exit, limited work space all

present a hazard.

There are also moving part inside the machine, therefore we should take care never enter our hand

inside the panel.

We should not move around the machine unless we have to. When moving it around, we must take

great care. We do not have much control because of its weight (Campbell, 2008).

Fire hazards:

There is a danger fire when using a laser device. It can occur inside the device or with the applicator

over the client (Campbell, 2008)..

We should always have and use the electrical fire extinguisher. It is best to use fire resistant material

for insulating the room and beam control.

Protective measures:

Three different type of protective measurement should be implemented for safe use of the laser

device.

Engineering measurement

Administration

Personal

64

Engineering:

Engineering controls will be the first line of defence, when it comes to preventing laser and its

ancillary hazards.

Ultra VPL machine has been designed and manufactured such to ensure high level of safety.

Some of the safety elements within the system are:

Key switch

Filtered viewing optic to protect the eyes

Hand piece holster

Earthed wire

Audible and visual emission indicating mechanism

Emission delay mechanism

In addition, it is important to follow the manufacturer’s advice carefully regarding service and

maintenance (Campbell, 2008).

Administration:

Campbell (2008) as followed explains the most important administrative protective measurements:

It is a good idea to obtain a copy of laser health and safety protection guidelines from the Non-

Ionizing Radiation Safety Committee, and follow their advices.

We must make sure that we are fully aware of and comply with the Standard Operating Procedures

(SOP).

We must always follow the advices by the Laser Protection adviser (LPA).

We need to check for local registration rules, and comply with them.

We must make sure that the equipment is serviced regularly with an authorized person. We need to

implement the laser safety officer’s guidelines.

Any organisation that uses laser equipments, must devise an approved, written standards

65

Outlining the operation, maintenance, and service procedures

Every single treatment carried out should be logged with the operator and the client details.

The clinic should be registered with health care commission and their set of rules and standards

should be closely followed.

The college has devised its own written standards that all the students need to comply to.

The laser machine must be restricted from the accessibility of unauthorized personnel.

Warning labels should be placed in a conspicuous places and all the protective devices must be clearly

labelled too.

Education and training should be provided for laser operators and maintenance personnel.

Access to the laser operating area needs to be restricted to allow entry only to personnel who have

been trained and who are listed on the Laser Safety Permit.

The laser system must operate by a key, and that key must be under control of an Authorized Laser

User at all times.

The area must be conspicuously posted to prevent inadvertent entry.

The area must be locked and the entrances interlocked to be able to stop the laser radiation in the case

of inadvertent entry.

Personal protection:

As the last line of defence, personal protective equipment must be worn when the laser system is in

operation, as operators, clients and other staff may be exposed to direct, reflected or scattered laser

beam.

The necessary personal protective equipments vary depending on the type of the laser system, its

power, and usage. Campbell(2008) lists some of the possible PPE required as bellow:

Laser protective Eyewear

Chemical protective clothing ( in case of using exogenous dye chromophore dyes, solvents, or

other chemicals)

Viewing filters

Radiation protective clothing and lotions

Masks

66

Although using some of these PPEs are optional or advisable, but using laser protective Eyewear is an

absolute necessity. In the case of all other protective measures failing, if we are wearing proper laser

safety glasses for the wavelength and the power of the laser we are using, we will protect our eyes.

Therefore, the importance of wearing laser safety glasses cannot be overemphasized.

As discussed earlier, different wavelengths interact with living tissues differently. We must bear in

mind that the same applies to the protective lenses we use. Each wavelength of laser beam requires a

specific type of lenses, which provide the optimum protection against that particular wavelength. On

type of lenses cannot protect our eyes against all different wavelength laser beams

(geocities.com/laser_biological_hazards_skin, 2008).

For example we must not use a pair of safety glasses that are rated to protect against 632 nm

wavelength, when we are using a 488 nm wavelength. The first factor to take into account when

choosing safety glasses is the wavelength.

The other important consideration with the laser protective eyewear is the optical density. Even if we

choose the proper lenses for a certain wavelength, lenses do not filter out all the light that might be

incident upon them, and not all lenses are rated the same. Therefore, it is necessary to take into

account the optical density of the laser system we use. The optical density (OD) is defined by

ANSIZ136.1 as the logarithm to the base ten of the reciprocal of transmittance:

OD = − log10t where t is t he transmittance (geocities.com/laser_biological_hazards_skin, 2008).

Generally it is strongly recommended to use the laser protective glasses, which are manufactured and

supplied by the company that we use their laser system, which is Energist in the case of Newcastle

college (Campbell, 2008).

Campbell also states other considerations that should be taken into account when choosing laser

protective glasses, as bellow:

Complying with contemporary standards

Good visible light transmission

Peripheral vision requirements

Prescription lenses

Allowing adequate ventilation

Comfort

Degradation of lenses material

Shock resistance

67

Damage threshold

There are some other points to remember.

Both wavelength and OD must be clearly labelled on either the temple for glasses, or on the frame,

for goggles.

The selection of proper protective eyewear is of paramount importance when considering eye safety.

The protective eyewear not only must provide protection from frontal and temporal exposures, but

also must be lightweight and comfortable to wear. In addition, it must allow for adequate ventilation.

Today’s manufacturers have tried to bear these in mind in designing new generation of laser safety

glasses. Glasses available today are not only comfortable and lightweight, but also they are stylish and

can be ordered with prescription lenses.

All protective eyewear must be inspected before each use to ensure that it will provide adequate

protection. Prior to using a pair of laser protective glasses, the lenses must be inspected for any deep

scratches and grooves. If any are found, the eyewear should not be used. The frame should also be

checked for any loose or missing temple screws and to ensure that the glasses comfortably fit our

face. It is most important to remember to check that the safety glasses will provide the proper

protection for the wavelength being used (geocities.com/laser_biological_hazards_skin, 2008).

68

References:

Acne scar treatment.net, 2008. Acne scar laser treatment [online]. Available at:

http://www.acnescarlasertreatment.html [Accessed 19 November 2008]

Akita, H. & Anderson R.R., 2004. Laser treatments in dermatology. The Journal of Cosmetic

Dermatology, 12 (06-2004), p.2-13.

Altshuler, G.B., Anderson, R.R. & Manstein, D., 2001. Extended theory of selective

photothermolysis. Lasers in Surgery and Medicine, 432(2001), p.416-432.

Anderson, R.R. & Parrish J.A., 1981. The optics of human skin. The Journal of Investigative

Dermatology, 77(1), p.13-19.

Bader, R.S., 2007. Cutaneous laser resurfacing: carbon dioxide. The Medscape journal [online],

November 2007. Available at: http://www.emedicine.com/derm/topic513.htm [Accessed 05 October

2008]

Bassel, M.H., 2007. Effects of visible light on the skin. Photochemistry and Photobiology, Mar/Apr

2008, p.10-27

Bentlon Ltd, 2004. Bentlon IPL dual power flash. [online]. Available at: http://www.bentlon.com

Cutting Technologies Ltd, 2008. Lasers: technical information., [online]. Available at:

http://www.cut-tec-.co.uk/lasers.htm [Accessed 27 November 2008]

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