“light sources and interaction of light with matter” · “light sources and interaction of...

““Light Sources and Interaction ofLight Sources and Interaction of

Light With MatterLight With Matter””IST 8A Lecture #3 - Jan. 12, 2005IST 8A Lecture #3 - Jan. 12, 2005

M. M. MolinaroMolinaro, F. , F. ChuangChuangIST 8A (Shedding Light on Life) - W05IST 8A (Shedding Light on Life) - W05

Lawrence LivermoreNational Laboratory

Sources of LightSources of Light

What do you think are some of theWhat do you think are some of thesources of light?sources of light?


IncandescenceIncandescence:: light emission by thermal radiation of a temperature high light emission by thermal radiation of a temperature highenough to render the source of radiation visible.enough to render the source of radiation visible.

ElectroluminescenceElectroluminescence:: light-emitting diode (LED) light-emitting diode (LED) LaserLaser: : light amplification through the stimulated emission of radiationlight amplification through the stimulated emission of radiation FluorescenceFluorescence:: light emission resulting from absorption of shorter-wavelength light emission resulting from absorption of shorter-wavelength

electromagnetic radiation. Persists for less than 10electromagnetic radiation. Persists for less than 10-8-8 sec after excitation. sec after excitation. PhosphorescencePhosphorescence:: similar to fluorescence, but persisting longer than 10 similar to fluorescence, but persisting longer than 10-8-8 sec sec

following excitation.following excitation. ChemiChemi- and Bio-luminescence- and Bio-luminescence:: e.g., the firefly e.g., the firefly Blackbody radiationBlackbody radiation:: ““purepure”” form of incandescence form of incandescence

Sources of Light - IncandescenceSources of Light - Incandescence

What is it and how does it work? IWhat is it and how does it work? Incandescencencandescence is the release of is the release ofelectromagnetic radiation from a hot body due to its high temperature. Theelectromagnetic radiation from a hot body due to its high temperature. Therelease of radiation is usually in the release of radiation is usually in the infraredinfrared ( (heatheat) and the visible region of the) and the visible region of theelectromagnetic spectrum (we perceive as light.) Incandescence occurs in bothelectromagnetic spectrum (we perceive as light.) Incandescence occurs in bothlight bulbs where the light bulbs where the electrical resistanceelectrical resistance to electron flow excites electrons in to electron flow excites electrons inthe material to jump to a higher orbit, and thus subsequently release a photon;the material to jump to a higher orbit, and thus subsequently release a photon;and when something is on fire or during an explosive or a combustion reaction.and when something is on fire or during an explosive or a combustion reaction.X-rays can also be produced by incandescence, but often most energy isX-rays can also be produced by incandescence, but often most energy iswasted in the form of heat. wasted in the form of heat. Tungsten bulb glows at 2700K.Tungsten bulb glows at 2700K.

Range of wavelengths produced Range of wavelengths produced IR and visibleIR and visible Energy efficiency: Energy efficiency: about 90% given off as heatabout 90% given off as heat

http://en.wikipedia.org/wiki/Incandescencehttp://en.wikipedia.org/wiki/Incandescent_light_bulb http://www.gwebdesign.de/company-en.html

Sources of Light - ElectroluminescenceSources of Light - Electroluminescence

What is it and how does it work? What is it and how does it work? ElectroluminescenceElectroluminescence is an is an opticalopticalphenomenonphenomenon and and electrical phenomenonelectrical phenomenon where a material such as a natural where a material such as a naturalblue diamond emits light when an electric current is passed throughblue diamond emits light when an electric current is passed throughit.Electroluminescence (EL) is mainly observed in it.Electroluminescence (EL) is mainly observed in semiconductorssemiconductors. The electric. The electricfield excites field excites electronselectrons in the material which then emit the excess energy as in the material which then emit the excess energy asphotons. photons. LEDs LEDs are the most well known example of electroluminescence.are the most well known example of electroluminescence.

Range of wavelengths produced Range of wavelengths produced (LED)(LED) is a is a semiconductorsemiconductor device that emits device that emitsincoherentincoherent monochromaticmonochromatic light light. . The wavelength of the light emitted dependsThe wavelength of the light emitted dependson the on the bandgap bandgap energy of the materials forming theenergy of the materials forming the pn pn junction. The materialsjunction. The materialsused for an LED haveused for an LED have bandgap bandgap energies corresponding to near-infrared, visibleenergies corresponding to near-infrared, visibleor near-ultraviolet light.or near-ultraviolet light.

Energy efficiency: Energy efficiency: 2 to 4 times more efficient than incandescent - less heat!2 to 4 times more efficient than incandescent - less heat!

http://en.wikipedia.org/wiki/Electroluminescencehttp://en.wikipedia.org/wiki/LED

http://www.fortrantraffic.com/signals/led/LED.htm

http://www.kolej.pl/modele/JTZ/obwody/swiatlo.html

Demo:Demo:RGB LEDRGB LED


LASERLASER = = LLight ight AAmplification through mplification through SStimulatedtimulatedEEmission of mission of RRadiationadiation

MonochromaticMonochromatic CoherentCoherent DirectionalDirectional Can focus to few hundred nm, high powerCan focus to few hundred nm, high power Range from UV to Visible to IR + some are tunableRange from UV to Visible to IR + some are tunable Can pulse down to Can pulse down to femtosecondsfemtoseconds

http://science.http://science.howstuffworkshowstuffworks.com/laser..com/laser.htmhtm

http://en.wikipedia.org/wiki/Laser


3. Excited atoms emitphotons in randomdirections

1. Ruby laser in non-lasing state

4. Photons travelingparallel to rod axis getreflected back andforth, exciting moreatoms in the process

2. Light flash excitesatoms in the ruby rod

5. Monochromatic,coherent, directionallaser beam exits frompartially mirroredsurface

How a Ruby Laser WorksHow a Ruby Laser Works

Sources of Light - FluorescenceSources of Light - Fluorescence

What is it and how does it work? What is it and how does it work? Fluorescence is the property of some atomsFluorescence is the property of some atomsand molecules to absorb light at a particular wavelength and to subsequentlyand molecules to absorb light at a particular wavelength and to subsequentlyemit light of longer wavelength after a brief interval, termed the fluorescenceemit light of longer wavelength after a brief interval, termed the fluorescencelifetime. The process of phosphorescence occurs in a manner similar tolifetime. The process of phosphorescence occurs in a manner similar tofluorescence, but with a much longer excited state lifetimefluorescence, but with a much longer excited state lifetime

Range of wavelengths produced Range of wavelengths produced Usually the fluorescent materials areUsually the fluorescent materials are““excitedexcited”” by shining UV light and they re-emit in the visible and infra-red. by shining UV light and they re-emit in the visible and infra-red.

Energy efficiency: Energy efficiency: 4 times more efficient than incandescent. Low heat!4 times more efficient than incandescent. Low heat!

http://en.wikipedia.org/wiki/Fluorescence

Inside the glass tube is a partial vacuum and a smallamount of mercury. An electric discharge in the tubecauses the mercury atoms to emit light. The emitted light isin the ultraviolet range and is invisible, and also harmful toliving organisms, so the tube is lined with a coating of afluorescent material, called the phosphor, which absorbsthe UV and re-emits visible light.

http://www.geology.wisc.edu/~museum/old/whatis3.html


http://micro.magnet.fsu.edu/primer/lightandcolor/fluorointroduction.htmlhttp://www.bris.ac.uk/Depts/Synaptic/info/imaging/imaging_1.htm

FluorescenceFluorescence:: light emission resulting from absorption of shorter-wavelength light emission resulting from absorption of shorter-wavelengthelectromagnetic radiation. Persists for less than 10electromagnetic radiation. Persists for less than 10-8-8 sec after excitation. sec after excitation.

http://micro.magnet.http://micro.magnet.fsufsu..eduedu/primer/techniques/fluorescence/excitation.html/primer/techniques/fluorescence/excitation.html


Dr. D. Talapin, University of Hamburg,http://www.chemie.uni-hamburg.de/pc/Weller/

http://www.qdots.com/live/render/content.asp?id=84

Quantum DotsQuantum DotsSources of Light - FluorescenceSources of Light - Fluorescence

Sources of Light - PhosphorescenceSources of Light - Phosphorescence How it works -How it works -

PhosphorescencePhosphorescence is a is aradiativeradiative transitiontransition involving a involving achange in the change in the spin multiplicityspin multiplicityof a molecule. Because of thisof a molecule. Because of thischange, thechange, the radiative radiative transitiontransitionis delayed, and theis delayed, and thephosphorescent material glowsphosphorescent material glowsa while after the incidenta while after the incidentillumination stops. Because ofillumination stops. Because ofthis, phosphorescent materialsthis, phosphorescent materialsare most commonly calledare most commonly called"glow-in-the-dark"."glow-in-the-dark".

http://www.valhallaarms.com/technology/lighting_fx.htm

http://images.iwoot.com/large/glofri_lg.jpg

http://www.olympusfluoview.com/theory/fluoroexciteemit.htmlhttp://en.wikipedia.org/wiki/Phosphorescence

Sources of Light - Sources of Light - Chemi Chemi and Bioluminescenceand Bioluminescence

How it works: How it works: ChemoluminescenceChemoluminescence (sometimes(sometimes""chemiluminescencechemiluminescence") is the emission of light") is the emission of light((luminescenceluminescence) as the result of a chemical reaction.) as the result of a chemical reaction.Most simply, given Most simply, given AA and and BB, with an excited, with an excitedintermediate intermediate ◊◊, we have,, we have,

[ [AA] + [] + [BB] ] --> --> [[◊◊] ] --> --> [[ProductsProducts] + light] + lightThe decay of the excited state[The decay of the excited state[◊◊] to a lower energy level] to a lower energy level

is responsible for the emission of light.is responsible for the emission of light. WhenWhen chemoluminescence chemoluminescence takes place in livingtakes place in living

organisms, the phenomenon is calledorganisms, the phenomenon is calledbioluminescencebioluminescence

http://en.wikipedia.org/wiki/Chemoluminescence and Bioluminescence

http://www.omniglow.co.uk/inpublisher/uploaded_images/snaplight_pk_ass.JPG

http://www.mbari.org/itd/retrospective/bioluminescence.html

Sources of Light - Sources of Light - Chemi Chemi and Bioluminescenceand Bioluminescence

LuminolLuminol : : Luminol is used by investigators to locate blood, even if it has beencleaned or removed. Using its natural property of chemiluminesence, it glows ifblood is present. The glow lasts for about 30 seconds and is blue. Luminol reactswith the iron in hemoglobin, a pigment present in blood.

http://en.wikipedia.org/wiki/Luminol

http://curiouslee.typepad.com/photos/best_of_curiouslee/firefly.html

How it works: How it works: A blackbody is an object that emits a well defined spectrum of radiationsolely based on its temperature. Blackbody temperature is the temperature of an object if itis reradiating all the thermal energy that has been added to it; if an object is not ablackbody radiator, it will not reradiate all the excess heat and the leftover will go towardincreasing its temperature.

Stefan-Stefan-Boltzmann Boltzmann lawlaw - overall power emitted per unit area. - overall power emitted per unit area. WienWien’’s s law - Defines strongest emissionlaw - Defines strongest emission Real objects never behave as full-ideal black bodies, and instead the emittedReal objects never behave as full-ideal black bodies, and instead the emitted

radiation at a given frequency is a fraction of what the ideal emission would be.radiation at a given frequency is a fraction of what the ideal emission would be.

Sources of Light - BlackbodySources of Light - Blackbody

http://www.astronomycafe.net/qadir/q72.html

HotterHotterColderColderEven as the peak wavelength moves into the ultra-violet enough radiation continues to be emitted inthe blue wavelenths that the body will continue to appear blue. It will never become invisible.

http://en.wikipedia.org/wiki/Blackbody

Sources of Light - IR emissionSources of Light - IR emission

ExamplesExamples

http://coolcosmos.ipac.caltech.edu/image_galleries

Demo:Demo:ThermometerThermometer

Interactive AppletInteractive AppletBlackbodyBlackbody

Sources of Light - BlackbodySources of Light - Blackbody

??Incoming photonIncoming photon

QQ: : What happens when photons hit matter..?What happens when photons hit matter..?

AA: : Both light and matter can be affected. Consider bothBoth light and matter can be affected. Consider bothFates of LightFates of Light, and , and Fates of MaterialFates of Material..!..!

??Target materialTarget material

Interaction of Light with MatterInteraction of Light with Matter

Incoming photonIncoming photon

Reflected photonReflected photon

Materials with highMaterials with highelectron density, suchelectron density, suchas metals (i.e., silver,as metals (i.e., silver,mercury, aluminum)mercury, aluminum)

ReflectionReflection: : The return of radiationThe return of radiationby a surface, without change inby a surface, without change inwavelength.wavelength.

Demo: Laser reflect, measure anglesDemo: Laser reflect, measure angles


Incoming photonIncoming photon Transmitted photonTransmitted photon

Materials like water,Materials like water,glass, plastic, etcglass, plastic, etc……

TransmissionTransmission: : The conduction of radiant energy through a medium.The conduction of radiant energy through a medium.



Transmitted photonTransmitted photonMaterials like water,Materials like water,glass, plastic, etcglass, plastic, etc……

RefractionRefraction: : CChange in direction of a wave dueto a change in velocity..

Demo: Vapor chamber + Demo: Vapor chamber + plexiglasplexiglas


Snell’s Law: n1sin(θ1) = n2sin(θ2)The refractive index of a material is the factorby which electromagnetic radiation is sloweddown (relative to vacuum) when it travels insidethe material. Glass 1.5-1.9, diamond 2.41

ray in the denser medium is always closer to the normal

http://en.wikipedia.org/wiki/Refraction

Interactive AppletInteractive AppletReflection and RefractionReflection and Refraction




Forward scatterForward scatter

Side scatterSide scatter

Back scatterBack scatter

ScatteringScattering: : The change in spatial distribution of a beam of radiation whenit interacts with a surface or heterogeneous medium. The sky blue becausemolecules in the air preferentially scatter blue light. Scattering varies as afunction of the ratio of the particle diameter to the wavelength of the radiation.

http://en.wikipedia.org/wiki/Scattering


DiffractionDiffraction: T: The apparent bending and spreading of waves when they meetan obstruction. Diffraction also occurs when any group of waves of a finitesize is propagating; for example, a narrow beam of light waves from a lasermust, because of diffraction of the beam, eventually diverge into a widerbeam at a sufficient distance from the laser.


??


Scattering Demo - Scattering Demo - tape andtape andplastic cupplastic cupDiffraction Demo - Diffraction Demo - LightLightthrough a slit or on a hairthrough a slit or on a hair


http://www.olympusmicro.com/primer/lightandcolor/diffraction.htm andhttp://www.olympusmicro.com/primer/java/diffraction/index.htmll



AbsorptionAbsorption: : The loss of light as it passes through a material,The loss of light as it passes through a material,generally due to its conversion to other energy forms.generally due to its conversion to other energy forms.

EnergyEnergy

Transforming EnergyTransforming Energy

ThermalThermal

ElectricalElectrical

ChemicalChemical

PhotonicPhotonic

KineticKinetic

HeatHeat

ElectricityElectricity

ChemistryChemistry

LightLight

MotionMotion

Interaction of Light with BiomaterialsInteraction of Light with Biomaterials

Incoming photonIncoming photon ReflectionReflectionAbsorptionAbsorptionTransmissionTransmissionScatteringScattering

In complex materials, any combination of interactions areIn complex materials, any combination of interactions arepossible. The exact nature of each process depends on thepossible. The exact nature of each process depends on thephysicalphysical andand chemical structurechemical structure of the biomaterial. of the biomaterial.

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