opti510r: photonics · different em waves have diff. wavelengths planck constant: h = 6.626068 x...
TRANSCRIPT
OPTI510R: Photonics
Khanh Kieu
College of Optical Sciences,
University of Arizona
Meinel building R.626
Important announcements
Homework #1 assigned, due Jan 24
No class Monday, Jan 21th
TA office hour: 3-4 PM, Wednesdays (8th floor breakout
area)
Properties of Light
Nature of light
Velocity of light
Frequency and wavelength
Polarization
Coherence
Other light characteristics
Nature of light
The nature of light has been a fascinating topic for many generations
of researchers. We all see and feel light but what it is exactly is still something
that challenges our minds.
17th century known facts about light:
• Light has different colors
• Light can travel through vacuum
• Light can be reflected and refracted
(Snel’s law)
i r
i = r
Nature of light
Corpuscular theory of light: light consists of corpuscles or
very small particles flying at a finite velocity (Isaac Newton).
Can be used to understand reflection, refraction and different colors of light
Isaac Newton
So what is light?
But fails to explain diffraction, interference and polarization of light
Nature of light
The wave theory of light: At first, the nature of light is thought of as wave propagating
in a medium called luminiferous aether. But all attempts to detect the aether have failed
so far. So the theory based on the aether was more or less abandoned. The
electromagnetic theory of light was then developed, culminating in the Maxwell’s
equations. In modern understanding, aether has no role in the theory of light.
Christiaan Huygens (1629-1695)
In 1845, Michael Faraday discovered
Faraday rotation
In 1873, Maxwell published his set of
equations
The Michelson–Morley
experiment (1887)
wikipedia.com
Nature of light
Christiaan Huygens (1629-1695)
In 1845, Michael Faraday discovered
Faraday rotation
In 1873, Maxwell published his set of
equations
Reflection, refraction, diffraction,
Interference, and polarization explained
The wave theory of light: At first, the nature of light is thought of as wave propagating
in a medium called luminiferous aether. But all attempts to detect the aether have failed
so far. So the theory based on the aether was more or less abandoned. The
electromagnetic theory of light was then developed, culminating in the Maxwell’s
equations. In modern understanding, aether has no role in the theory of light.
Electromagnetic Waves (EM)
Infrared-waves
Wavelength dimensions of sub-mm to micron
Infrared waves are thermal
Image of a small dog in mid-infrared lightInfrared LED in remote control
Credit: Prof. Norwood
Infrared-waves
Telecommunication bands
Thermal imaging, remote sensing
Measuring the temperatures
of clouds
Credit: Prof. Norwood
Visible-waves
Wavelength dimensions of 0.38 to 0.78 microns
Human eye is most sensitive at 555mm
Credit: Prof. Norwood
Ultraviolet-waves
Wavelength dimensions of 10 to 200 nm
Sun emits UV radiation. Prolong exposure is bad for
skin, eye and immune system. Exposure is needed
for generation of Vitamin D.
Credit: Prof. Norwood
Nature of light
Christiaan Huygens (1629-1695)
In 1845, Michael Faraday discovered
Faraday rotation
In 1873, Maxwell published his set of
equations
Reflection, refraction, diffraction,
Interference, and polarization explained
But… Photoelectric effect, black body
radiation, Compton effect not explained
The wave theory of light: At first, the nature of light is thought of as wave propagating
in a medium called luminiferous aether. But all attempts to detect the aether have failed
so far. So the theory based on the aether was more or less abandoned. The
electromagnetic theory of light was then developed, culminating in the Maxwell’s
equations. In modern understanding, aether has no role in the theory of light.
Nature of light
The corpuscular theory of light came back?
The quantum theory of light: In an attempt to explain blackbody radiation,
Planck postulated that electromagnetic energy could be emitted only in quantized
form, in other words, the energy could only be a multiple of an elementary unit,
, where h is Planck's constant.
The classical physics prediction was completely wrong! (It said that an infinite
amount of energy should be radiated by an object at finite temperature)
Different EM waves have diff. wavelengths
Planck constant: h = 6.626068 x 10-34 m2kg/s
/hchE
Nature of light
Wave-particle duality: OK! It must be both wave and particle then!
de Broglie formulated the de Broglie
hypothesis in 1924- all matter has a wave-
like structure (1929 Nobel prize):
Confirmed by electron
Interference (1937 Nobel prize)
Book by de Broglie
http://iopscience.iop.org/article/10.1088/1367-2630/15/3/033018/meta
Velocity of light
The velocity of light is a fundamental constant in physics. c = 299,792,458m/s
Maxwell proposed that light travel with the speed of light 1865.
Einstein postulated that the speed of light with respect to any inertial frame
is independent of the motion of the light source.
According to special relativity, c is the maximum speed at which all energy,
matter, and information in the universe can travel.
At the moment the meter is defined through the speed of light
How to measure the velocity of light?
Measure the velocity of light
Rømer Observation: Delay in the time of eclipses of the moon as observed from earth
Measure the velocity of light
Fizeau apparatus
(c = 315000 km/s)Foucault apparatus
(c = 298000±500 km/s)
Source: wikipedia.com
Measure the velocity of light
Measure the velocity of light
• In 1983: "The meter is the length of the path travelled
by light in vacuum during a time interval of
1/299792458 of a second.“
• As a result of this definition, the value of the speed of
light in vacuum is exactly 299 792 458 m/s
Measure the velocity of light
Astronomical measurements
Time of flight measurement
Cavity resonance
Electromagnetic constants
Interferometry
1675 Rømer and Huygens,
moons of Jupiter
220000
1729 James Bradley,
aberration of light
301000
1849 Hippolyte Fizeau,
toothed wheel
315000
1862 Léon Foucault,
rotating mirror
298000±500
1907 Rosa and Dorsey, EM
constants
299710±30
1926 Albert Michelson,
rotating mirror
299796±4
1950 Essen and Gordon-
Smith, cavity resonator
299792.5±3.0
1958 K.D. Froome,
radio interferometry
299792.50±0.10
1972 Evenson et al.,
laser interferometry
299792.4562±0.0011
1983 17th CGPM,
definition of the metre
299792.458 (exact)
Velocity of light-Practical uses
LiDAR
3D imaging
GPSWikipedia.com
osa-opn.orghttp://theexceptioncatcher.com/p/GizGPSBth#.Ut8x2vTn-IU
Frequency and wavelength of light
Frequency and wavelength of light
The wavelength of light changes in a medium.
How about the frequency?
The wavelength of light defines the smallest spot size
that the laser beam can be focused down to.
Diffraction limit
How to measure frequency and
wavelength of light?
OSA (Optical spectrum analyzer)
The oscillation frequency of visible light is too fast to be measured
with conventional electronics directly.
How to measure frequency and
wavelength of light?
A high-resolution spectrum of CO2
in the near-IR was obtained using a Fourier-transform spectrometer (laserfocusworld.org)
Fourier-transform
spectrometer
How to measure frequency and
wavelength of light?
Fourier-transform
spectrometer
Fast acquisition speed, high resolution, low cost
Momentum of light
The momentum of light:
Angular momentum of light?
Wikipedia.com
NASA
spin angular momentum orbital angular momentum
Polarization
Linear polarization
Circular polarization
Elliptical polarization
Unpolarized light
How to measure the polarization state of a light beam?
Polarization
Optical Isolators
Imaging
All-optical switching
Magnetometer
…
Coherence
Temporal coherence
Spatial coherence
Applications: Interferometry,
coherent communication, imaging (OCT)…
Other light characteristics
Spectral bandwidth (OSA)
Average power, peak power (power meter)
Pulse energy, repetition rate (energy meter)
Intensity
Divergence, beam quality (M2 measurement)
Properties of Light
Nature of light
Velocity of light
Frequency and wavelength
Polarization
Coherence
Other light characteristics
Question for thoughts
Can you come up with your own theory of light?
Why light travels at the speed that it travels?
Can we use light to propel a satellite into its orbit?
Can you come up with a better way to measure the speed
of light?
Can something move faster that the speed of light?
Good books to read
Book by de Broglie (1937) by Albert Einstein and
Leopold Infeld (1967)by Thomas Kuhn (4th ed. 2012)