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Polarized Light and Polarimetry OPTI 623 Spring 2012 © Russell A. Chipman
orientation
Russell A. Chipman
OPTI 623
Spring 2012
DOLP
Polarized Light and Polarimetry
2
Section
Polarization in Nature
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Sky polarization
Natural scene polarization
Cloud polarization
Sun polarization
Solar system polarization
IR black body polarization
Polarized Light and Polarimetry OPTI 623 Spring 2012 © Russell A. Chipman
Humans Have Little Polarization Sensitivity
• <3% polarization
sensitivity
• Rhodopsin is randomly
oriented
• Weak polarization
dependent absorption
in nerves around fovea
• Hadinger’s brush
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Many Animals Have Polarization Vision
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Bees
Ants
Butterflies
Octopus
Squid
Cuttlefish
Salmon
Lobsters, some species can also signal with polarization
Dung Beetles
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Polarized Light and Polarimetry OPTI 623 Spring 2006 © Russell A. Chipman
1/31/2006
Polarization Pattern in Blue Sky
Polarized Light and Polarimetry OPTI 623 Spring 2012 © Russell A. Chipman
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Sky and Cloud Polarization
• Ground Multi-Spectral Polarimetric
Imager (MSPI) Image taken June
22, 2010 at 9:00 AM
• Scene is looking to the East
Polarized Light and Polarimetry OPTI 623 Spring 2012 © Russell A. Chipman
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Stokes Parameters
I  I 0  I90
I  I 45  I135
I – Total Intensity of scene
Q – 0° or 90° polarization
U - 45° or 135° polarization
Q  I 0  I 90
-Q
U  I 45  I135
+U
+Q
-U
Polarized Light and Polarimetry OPTI 623 Spring 2012 © Russell A. Chipman
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Meridian Coordinates
• Horizontal Polarization is the
projection on Latitude
• Vertical polarization is
projection on Longitude
+Q
-Q
Polarized Light and Polarimetry OPTI 623 Spring 2012 © Russell A. Chipman
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Representations of Polarization
Clouds have much less polarization than sky
Degree of Linear Polarization
Angle of Linear Polarization
Q2  U 2
DoLP 
I
AoLP 
U 
1
tan1  
2
Q
Polarized Light and Polarimetry OPTI 623 Spring 2012 © Russell A. Chipman
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Automobile’s
orientation
DOLP
Intensity at 660 nm
Degree of Linear Polarization
Orientation
Yellow – horizontal
Blue - vertical
Polarized Light and Polarimetry OPTI 623 Spring 2012 © Russell A. Chipman
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Color Coding Intensity, DoLP, Orientation
Dim
Medium
Bright
The representation of intensity (S0) as brightness
DoLP as saturation from white for unpolarized light to fully
saturated for linearly polarized light
Orientation of polarization as hue: red 0°, yellow green 45°, cyan
90°, purple 135°. (left) low S0, (middle) intermediate S0, (right)
maximum S0.
Polarized Light and Polarimetry OPTI 623 Spring 2012 © Russell A. Chipman
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Stokes parameters Q, U are measured. Degree of Linear
Polarization (DOLP) and polarization orientation are extracted
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Polarized
Light and Polarimetry OPTI 623 Spring 2012 © Russell A. Chipman
orientation
DOLP
U
Polarization contains information about
material texture and orientation
Q
Multi-angle Spectro-Polarimetric Imager (MSPI)
Automobile Example
Polarized Light and Polarimetry OPTI 623 Spring 2012 © Russell A. Chipman
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Another Automobile
Polarized Light and Polarimetry OPTI 623 Spring 2012 © Russell A. Chipman
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Natural Polarization Scenes
Polarization Image of a Parking Lot
• A few areas of high linear polarization on cars.
• Polarization orientation is related to object orientation.
S0, Intensity
Degree of Linear Polarization
Angular Orientation of Polarization
Degree of Circular Polarization
Circular polarization below 3%.
Polarized Light and Polarimetry OPTI 623 Spring 2012 © Russell A. Chipman
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Natural Polarization Scenes
• Polarization image of bus.
• Polarization orientation is
related to object
orientation.
• Low Degree Of Linear
Polarization for lawn in
background and front of
bus in shade.
• Degree Of Circular
Polarization below 3%.
S0, Intensity
DOLP
Orientation
DOCP
Polarized Light and Polarimetry OPTI 623 Spring 2012 © Russell A. Chipman
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Natural Polarization Scenes
S0, Intensity
DOLP
• Low Degree Of Linear
Polarization for lawn in
background and front of
bus in shade.
Polarized Light and Polarimetry OPTI 623 Spring 2012 © Russell A. Chipman
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Natural Polarization Scenes
• Polarization image of bus.
• Polarization orientation is
related to object
orientation.
• Polarization orientation
follows shape of bus
• Note car on right
Orientation
Polarized Light and Polarimetry OPTI 623 Spring 2012 © Russell A. Chipman
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Natural Polarization Scenes
• Polarization image of bus.
• Degree Of Circular
Polarization below 3%
• Most probably noise
• Usually little circular
polarization in natural
scenes.
DOCP
Polarized Light and Polarimetry OPTI 623 Spring 2012 © Russell A. Chipman
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Polarized Light and Polarimetry OPTI 623 Spring 2012 © Russell A. Chipman
Time Sequence of False Color Intensity Images
• From Meinel Building looking east image
•Red –
865 nm
•Green –
660 nm
•Blue –
470 nm
10:00am
11:21am
12:43pm
1:59pm
2:49pm
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Polarized Light and Polarimetry OPTI 623 Spring 2012 © Russell A. Chipman
Time Sequence of Multi-Wavelength DoLP Images
• From Meinel Building looking east image
• Black – unpolarized at all wavelengths
•Red –
865 nm DoLP
•Green –
660 nm DoLP
• Grey & White – equal DoLP at all
wavelengths
•Blue –
470 nm DoLP
• Blue – blue light has highest DoLP
10:00am
11:21am
12:43pm
1:59pm
2:49pm
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(multi-OPTI
l) 623 Spring 2012 © Russell
Polarized LightDOLP
and Polarimetry
A. Chipman
Time Sequence of 660 nm Angle of Linear Polarization Images
• Meinel Builiding looking east image
• Sun directly above 10:00 am image, moving up and to right
• Steady polarization rotation of most pixels associated with su motion
• Noisy in dark regions
10:00am
11:21am
12:43pm
AoLP (660nm)
1:59pm
2:49pm
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Polarized Light and Polarimetry OPTI 623 Spring 2012 © Russell A. Chipman
Meinel Opt.Sci.
building
I
6/24/2010
4:08PM (Az time)
DOLP
1st col: multi-l (R,G,B)
2nd column: Red
3rd column: Green
4th column: Blue
AOLP
Using Canon DSLR
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Polarized Light and Polarimetry OPTI 623 Spring 2012 © Russell A. Chipman
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Polarization Images
Vehicles crossing field
Infrared 10 micron
D. Chenault
Polaris Sensor Systems
Huntsville, AL
Polarized Light and Polarimetry OPTI 623 Spring 2012 © Russell A. Chipman
Automobile in Shade
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Intensity
660 nm Ground MSPI
Meinel parking lot
9:23 am, June 11, 2010
Polarized Light and Polarimetry OPTI 623 Spring 2012 © Russell A. Chipman
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Automobile in Shade
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Intensity
Degree of Linear Polarization
660 nm Ground MSPI
Meinel parking lot
9:23 am, June 11, 2010
Polarized Light and Polarimetry OPTI 623 Spring 2012 © Russell A. Chipman
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Imaging into
Shadows
Example
June112010_0923_images
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Polarized
Light and Polarimetry OPTI 623 Spring 2012 © Russell A. Chipman
Imaging Into Water Example
• Tub of water with
polarizers at bottom
• Next slide, milk is
added to water
29Chipman
Polarized Light and Polarimetry OPTI 623 Spring 2012 © Russell A.
Imaging Into Water Examples
• 55 ml of milk added to 30 L of water
• Even at low visibility, DOP image
shows location of polarizers
• Angle of polarization image conveys
polarizer orientation
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Polarized
Light and Polarimetry OPTI 623 Spring 2012 © Russell A. Chipman
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Color conveys information on the
composition of materials:
Green
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Blue
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chlorophyll
green paint or dye
copper
water with chlorophyll in it
sky
water
blue paint or dye
Quantum mechanical bond energies
Polarization conveys information on the direction of electron
oscillation during light emission.
Polarized Light and Polarimetry OPTI 623 Spring 2012 © Russell A. Chipman
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During light scattering
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Incident light applies forces along direction of light polarization
Electrons respond by oscillating
Radiate a polarization state based on electronic motions
Polarization conveys a projection of electronic motions along
the line of sight
• Polarization conveys indirect information on the illuminating
polarization state
• Therefore, polarization must reveal indirectly the orientation,
refractive index, and texture of surfaces.
Polarized Light and Polarimetry OPTI 623 Spring 2012 © Russell A. Chipman
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Polarization reveals indirectly the
orientation, refractive index, and texture of
the materials
• Polarization is the “orientation of the light”
• Polarization is the result of the “orientation of atomic oscillations”
• Technological advances in optics, mechanics, and computing are
bringing polarimetry from research area into a practical metrology
technique with many important applications.
Polarized Light and Polarimetry OPTI 623 Spring 2012 © Russell A. Chipman
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GroundMSPI
Multiangle Spectro-Polarimeter Imager
• Push-broom camera operation with FOV of 30°
• Measures linear polarization at 470, 660, and 865nm
• Photoelastic modulator based polarimeter
Polarized Light and Polarimetry OPTI 623 Spring 2012 © Russell A. Chipman
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Cloud Polarization
• Some clouds exhibit different polarization than sky
• Sky Polarization due to Rayleigh Scattering in the atmosphere
• Cloud Polarization can be due to
– Rayleigh Scattering
– Mie Single Scattering
– Multiple Scattering
Polarized Light and Polarimetry OPTI 623 Spring 2012 © Russell A. Chipman
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Cloud in detail
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Camera produces large 90° sweep
Small cloud
Stands alone – not influenced from light from other clouds
Scatter angle θ =
140°
Scene is to the East
θ
Polarized Light and Polarimetry OPTI 623 Spring 2012 © Russell A. Chipman
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Cloud in detail: 470 nm
• Brightness – Intensity
• Saturation – DoLP
• Hue - AoLP
Composite image
Polarized Light and Polarimetry OPTI 623 Spring 2012 © Russell A. Chipman
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Cloud in detail: 660 nm
• Higher contrast in Intensity
• Decrease in DoLP
• Portions of the cloud shares same
polarization orientation as the sky
• Other portions of the cloud change in
angle by about 90°
Composite image
Polarized Light and Polarimetry OPTI 623 Spring 2012 © Russell A. Chipman
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Cloud in detail: 865 nm
• Highest contrast in Intensity
• Lowest DoLP wavelength
• Much of the cloud orientation
polarization changes with respect to
the sky by about 90°
Composite image
Polarized Light and Polarimetry OPTI 623 Spring 2012 © Russell A. Chipman
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Cloud in detail
• Polarization state shown as
a vector
– Magnitude: DoLP
– Angle: AoLP
Red: 865 nm
Green: 660 nm
Blue: 470 nm
Polarized Light and Polarimetry OPTI 623 Spring 2012 © Russell A. Chipman
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Panoramic Scene
Combination
Image
Brightness –
Intensity
Saturation –
DoLP
Hue - AoLP
SE
SW
Angle of
Linear
Polarization
Polarized Light and Polarimetry OPTI 623 Spring 2012 © Russell A. Chipman
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Polarization During Light Scattering
• Incident light applies forces along direction of light’s E-field.
• Electrons respond by oscillating and radiate a polarization state
based on electronic motions.
• Polarization conveys a projection of electronic motions along
the line of sight.
• Therefore, polarization reveals indirectly the orientation,
refractive index, and texture of surfaces.
• Polarization is the “orientation of the light”.
• And polarization conveys indirect information on the illuminating
polarization state.
Polarized Light and Polarimetry OPTI 623 Spring 2012 © Russell A. Chipman
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Stars
• Most unpolarized
• Some high magnetic field stars are by a few percent
Polarized Light and Polarimetry OPTI 623 Spring 2012 © Russell A. Chipman
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So, how is the Sun polarized?
Polarized Light and Polarimetry OPTI 623 Spring 2012 © Russell A. Chipman
Sun
• Majority of wavelengths are unpolarized, but
Polarized Light and Polarimetry OPTI 623 Spring 2012 © Russell A. Chipman
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Sun
• Majority of wavelengths are unpolarized, but
• Zeeman scattering causes polarization dependent spectral line
splitting in many absorption bands
Polarized Light and Polarimetry OPTI 623 Spring 2012 © Russell A. Chipman
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• A side-by-side comparison of the solar surface, and the magnetic
image showing (red color) intense regions of magnetism near
sunspots. (Courtesy; UCAR - National Solar Observatory)
Polarized Light and Polarimetry OPTI 623 Spring 2012 © Russell A. Chipman
Magnetogram (mag.'net.o.gram)
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A magnetogram is an image that shows the strength of the magnetic field in the
direction of the line of sight.
Magnetograms are constructed from two a right and left circularly polarized narrow
band images taken in a spectral line that is sensitive to the magnetic field.
Grey areas in a magnetogram indicate that there is no magnetic field in the direction
of the line of sight, while black and white areas indicate regions where there is such
magnetic field.
Magnetogram Example
November 25, 2000
3/2/2005
MUG Meeting, Tucson
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Polarized Light and Polarimetry OPTI 623 Spring 2012 © Russell A. Chipman
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Zeeman Splitting on Sun
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Left: Spectrometer
slit crossing a
solar flare (vertical
black line)
Right: Spectrum
as function of
position on slit.
Near center,
Zeeman splitting
clearly visible in
center line.
http://rigel.csi.cuny
.edu/rowan/lecture
s/06a-The-SunLecture-SP_2006(part-1).pdf
Polarized Light and Polarimetry OPTI 623 Spring 2012 © Russell A. Chipman
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Polarized Light and Polarimetry OPTI 623 Spring 2012 © Russell A. Chipman
Solar spectral image of the Stokes parameters
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Example of a Stokes
vector spectral image
along monochromator
slit
Four simultaneous
images of the four
Stokes parameters.
Measured ZIMPOL
solar
spectropolarimeter in
a magnetized solar
region
Polarized Light and Polarimetry OPTI 623 Spring 2012 © Russell A. Chipman
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Polarization in the Solar System
Polarized Light and Polarimetry OPTI 623 Spring 2012 © Russell A. Chipman
Stokes parameter image of the Jupiter
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Linear Stokes
parameter
images of Jupiter
with the
wavelength in Ǻ.
Positive Q/I
(S1/S0) is parallel
to the rotation
axis (vertical).
Positive S2 is
rotated 45°
counterclockwise
from vertical.
ZIMPOL at the
Swiss IRSOL
solar telescope
in 2001.
Polarized Light and Polarimetry OPTI 623 Spring 2012 © Russell A. Chipman
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Stokes parameter image of the Saturn
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Linear Stokes
parameter
images of Saturn
with the
wavelength in Ǻ.
Positive Q/I
(S1/S0) is parallel
to the rotation
axis (vertical).
Positive S2 is
rotated 45°
counterclockwise
from vertical.
ZIMPOL at the
Swiss IRSOL
solar telescope
in 2001.
Polarized Light and Polarimetry OPTI 623 Spring 2012 © Russell A. Chipman
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Stokes parameter image of the Moon
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Linear Stokes
parameter
images of Moon
with the
wavelength in Ǻ.
Positive Q/I
(S1/S0) is parallel
to the rotation
axis (vertical).
Positive S2 is
rotated 45°
counterclockwise
from vertical.
ZIMPOL at the
Swiss IRSOL
solar telescope
in 2001.
Polarized Light and Polarimetry OPTI 623 Spring 2012 © Russell A. Chipman
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Black Body Emission Polarization
Aluminum IR Emissivity
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Light refracts out of the material
Fresnel’s equations for
transmission apply to the emitted
light
– Unpolarized at normal emission,
perpendicular
– P-polarized at non-normal
emission
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Smooth surfaces preferentially emit
p-polarized light
Aluminum example
p-polarization
s-polarization
Degree of Linear
Polarization
Polarized Light and Polarimetry OPTI 623 Spring 2012 © Russell A. Chipman
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Black Body Polarization Patterns
Reflection and Emission, Smooth Spherical Objects
• Surfaces preferentially reflect s-polarization
• Hot bodies emit more p-polarized light
• Cold bodies reflect more s-polarized light
Hot
Thermal
Equilibrium
Cold
• At equilibrium, reflection and emission are balanced, unpolarized.
Polarized Light and Polarimetry OPTI 623 Spring 2012 © Russell A. Chipman
Shape Estimation for Smooth Hot Blackbodies
Degree of Linear Polarization Patterns
Sphere
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Tilted Plate
Cylinder
Degree of linear polarization increases toward edges and indicates slope.
Ambiguous whether surfaces are tilted toward or away, concave or convex.
Polarized Light and Polarimetry OPTI 623 Spring 2012 © Russell A. Chipman
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Experimental Verification of Black
Body Polarization
Degree of Linear Polarization
• Germanium surface
• 3-5 micron
• Data includes both
significant emission
and reflection
• Both above and below
equilibrium
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Howe, et. al.. Proc. SPIE Vol. 4133 (2000).
Polarized Light and Polarimetry OPTI 623 Spring 2012 © Russell A. Chipman
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IR Imaging Polarimetry
for Landmine Detection
• Natural scenes are nearly unpolarized.
• Manmade objects have some linearly polarized light, especially
around edges.
• IR Imaging Polarimetry can assist mine detection.
Polarized Light and Polarimetry OPTI 623 Spring 2012 © Russell A. Chipman
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Day
Day
Night
Intensity
Degree of
Linear
Polarization
Polarized Light and Polarimetry OPTI 623 Spring 2012 © Russell A. Chipman
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End
Polarized Light and Polarimetry OPTI 623 Spring 2012 © Russell A. Chipman
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End
Polarized Light and Polarimetry OPTI 623 Spring 2012 © Russell A. Chipman
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Rainbows
Polarized Light and Polarimetry OPTI 623 Spring 2012 © Russell A. Chipman
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