modern optics lab lab 5 part 1: experiments involving light polarization measuring light...
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Modern Optics LabLab 5 Part 1: Experiments involving Light Polarization
Measuring light transmission through a dichroic material (“polarizer sheet”) as a function of polarization angle to verify Malus’ Law
Using polarization by reflection to determine the Brewster angle and then calculate the index of refraction of the reflecting material.
Qualitative observation of light polarization by scattering.
Topics
Modern Optics LabLab 5 Part 1: Experiments involving Light Polarization
Linearly polarized light
Modern Optics LabLab 5 Part 1: Experiments involving Light Polarization
Dichroic Absorption
Passes Is absorbedPartially absorbed and partially passes
Modern Optics LabLab 5 Part 1: Experiments involving Light Polarization
Dichroic Absorption
Partially absorbed and partially passes
E
E
||E cos|| EE
2Intensity E
222|| cosIntensity dTransmitte EE
(Malus’ Law)
Modern Optics LabLab 5 Part 1: Experiments involving Light Polarization
Polarization Dependent Reflection
tn
ini r
t
angleincident :i
angle reflected :r
angle ed transmitt:t
tr 180
Incident plane: Plane that contains incident, reflected and transmitted ray.
Modern Optics LabLab 5 Part 1: Experiments involving Light Polarization
Polarization Dependent Reflection
tn
in
Incident plane: Plane that contains incident, reflected and transmitted ray.
“Parallel polarized” light.
(parallel to incident plane) “p-polarized”
(p as in “parallel”)
Modern Optics LabLab 5 Part 1: Experiments involving Light Polarization
Polarization Dependent Reflection
tn
in
Incident plane: Plane that contains incident, reflected and transmitted ray.
“Perpendicular polarized” light. (perpendicular to incident plane)
“s-polarized” (s as in “senkrecht”)
Modern Optics LabLab 5 Part 1: Experiments involving Light Polarization
Fresnel Equations
Reflection Coefficients:
ti
ti
tiit
tiit
i
r
nn
nn
E
Er
tan
tan
coscos
coscos
||0
0||
ti
ti
tiit
ttii
i
r
nn
nn
E
Er
sin
sin
coscos
coscos
0
0
Reflection coefficients (relate to Electric field strength ratios)
For parallel polarized light:
For perpendicular polarized light:
Modern Optics LabLab 5 Part 1: Experiments involving Light Polarization
Modern Optics LabLab 5 Part 1: Experiments involving Light Polarization
Reflectances (relate to intensity ratios):
ti
tirR
2
22
|||| tan
tan
ti
tirR
2
22
sin
sin
Modern Optics LabLab 5 Part 1: Experiments involving Light Polarization
Brewster angle: R||=0
9090tantan
tan 22
22
||||
tititi
tirR
Modern Optics LabLab 5 Part 1: Experiments involving Light Polarization
Brewster Angle
tn
in
“Parallel polarized” light is not reflected at all if
incident under the “Brewster Angle”
90
Brewsteri
iii
ii
i
ii
t
iitiitt nnnnnnn
tan
cos
sin
90sin
sin
sin
sinsinsin
iit nn tan
Modern Optics LabLab 5 Part 1: Experiments involving Light Polarization
tn
inReflected light is s-polarized
under the Brewster angle.
90
Brewsteri
Modern Optics LabLab 5 Part 1: Experiments involving Light Polarization
Radiation pattern from an accelerated charge
e- Radiation is polarized
Modern Optics LabLab 5 Part 1: Experiments involving Light Polarization
Radiation pattern from an accelerated charge
e-
Length of arrow indicates intensity in that direction
Modern Optics LabLab 5 Part 1: Experiments involving Light Polarization
Scattered light
e-
incoming light
nothing scattered in this direction
scattered light
nothing scattered in this direction
Modern Optics LabLab 5 Part 1: Experiments involving Light Polarization
Scattered light
e-
incoming light
nothing scattered in this direction
scattered light
nothing scattered in this direction
Modern Optics LabLab 5 Part 1: Experiments involving Light Polarization
Scattered light
incoming light-unpolarized
scattered light
polarized
e-
polarized
Modern Optics LabLab 5 Part 1: Experiments involving Light Polarization
Rayleigh Scattering62
2
24
2
2
22
12
2
cos1 light scattered ofIntensity
d
n
n
RII o
incoming light
particle todistanceR
particle of refraction ofindex n particle ofdiameter d
Modern Optics LabLab 5 Part 1: Experiments involving Light Polarization
Intensity of scattered light
incoming light-unpolarized
e- 2cos10 2
1cos190 2
1cos190 2
2cos1180 2
1cos190 2
1cos190 2
62
2
24
2
2
22
12
2
cos1
d
n
n
RII o
Modern Optics LabLab 5 Part 1: Experiments involving Light Polarization
Color of scattered light
incoming light assume equal color intensity
62
2
24
2
2
22
12
2
cos1
d
n
n
RII o
Unscattered light
Scattered light
Looking at sunset
Looking at sky above
Modern Optics LabLab 5 Part 1: Experiments involving Light Polarization
Experimental Details: Using the Photometer to Measure Intensity
0 3
0
10
Zero Adjust
VariableSensitivityProbe Input
1000
3003
1CAL.
“Zero” adjustment:Start with “Sensitivity” 1000 (least Sensitive)Close off “Probe Input” with rubber stopper so that no light enters.Use Zero Adjust button to get needle to zero.Go to more sensitive setting (lower number) and zero, etc.
Measurement of Intensity:Start with “Sensitivity” 1000 (least Sensitive)Plug fiber optic cable into “Probe Input”.Step by step increase sensitivity but make sure needle stays within range.
See pages 19 ff of the “Advanced Optics Manual” for detailed operating instructions!!
Modern Optics LabLab 5 Part 1: Experiments involving Light Polarization
V.A Dichroic Absorption
Is the laser polarized?
Laser
PolarizerScreen
Modern Optics LabLab 5 Part 1: Experiments involving Light Polarization
V.A Measuring I() and verifying Malus’ Law
Zero Photometer Attach fiber optic cable to photometer and to rotational stage (tighten screw only very
lightly otherwise fiber optic cable may break internally). Do not bend fiber optic cable too tightly.
Top view
Laser
Fiber Optic Cable
Photometer
Polarizer
Measure I(). Plot I() versus cos2.
Modern Optics LabLab 5 Part 1: Experiments involving Light Polarization
V.A Measuring I() with two polarizers
Laser
Polarizer 1Screen
Polarizer 2 on)polarizatilaser to(
Vary the orientation of polarizer 1. Measure I() plot versus . Explain results.
Modern Optics LabLab 5 Part 1: Experiments involving Light Polarization
V.B Orienting the laser polarization to be horizontal
Rotate laser so that E-vector is horizontal (from V.A. you should know approximate orientation already).
With polarizer oriented as shown, fine tune the laser orientation until light transmission is minimized.
Top view
Laser
Polarizer (0-180 direction vertical)
Screen
Modern Optics LabLab 5 Part 1: Experiments involving Light Polarization
V.B Adjusting the glass plate
Front surface of glass plate should be hit by laser exactly at the rotation axis of the rotation stage.
Calibrate the zero degree position by using the back-reflection of the laser.
Top view
Laser
Glass plate
Short component holder
Polarizer (0-180 direction vertical)
Modern Optics LabLab 5 Part 1: Experiments involving Light Polarization
V.B Finding the Brewster angle
Rotate until reflection intensity is minimized to find the Brewster angle. Calculate the index of refraction of glass from the Brewster angle.
Top view
Laser
Polarizer (0-180 direction vertical)
Screen
Modern Optics LabLab 5 Part 1: Experiments involving Light Polarization
V.B Adjusting the glass plate
Front surface of glass plate should be hit by laser exactly at the rotation axis of the rotation stage.
Adjust 127mm lens so that sharp image of filament is seen on back side of lens holder.
Adjust glass plate orientation so that filament image is in the middle of lens holder.
Top view
Glass plate
Short component holder
Incandescent Light
200mm
127mm lens
Approx.330mm
Filament image
Approx.750mm
Modern Optics LabLab 5 Part 1: Experiments involving Light Polarization
V.B Adjusting lens position and getting Brewster angle
Rotate rotational stage by approx. 30 degrees. Readjust lens position so that filament is in focus on the screen. With polarizer select parallel polarization component. Look at intensity versus incident
angle. Then do the same for perpendicular polarization component. Make a qualitative comparison of I() for the two components. Determine the Brewster angle again.
Top viewIncandescent Light
Screen
Polarizer
127mm lens
Modern Optics LabLab 5 Part 1: Experiments involving Light Polarization
V.C Polarization by Scattering
Front surface of glass plate should be hit by laser exactly at the rotation axis of the rotation stage.
Adjust 127mm lens so that sharp image of filament is seen on back side of lens holder.
Adjust glass plate orientation so that filament image is in the middle of lens holder.
Top view
Screen
Murky water
Incandescent Light
48mm lens
Approx. 4cm
Look from side (and look from top)through polarizer
Modern Optics LabLab 5 Part 1: Experiments involving Light Polarization
V.C Scattering of polarized laser light
Look from side (and then from top down). Observe scattered light intensity as you rotate the laser’s polarization.
Top view
Screen
Murky water
Laser
Look from side (and look from top)through polarizer