announcements 10/29/12 prayer clement will be out of town on friday, no office hours exam 2 ends...
TRANSCRIPT
Announcements 10/29/12 Prayer Clement will be out of town on Friday, no
office hours Exam 2 ends tomorrow
Pearls Before Swine
From warmup
Extra time on?a. polarization by reflection (3 students)
Other comments?a. Do we really have homework due on a
national holiday?
From warmup
What does it mean to say that a given light beam is polarized? Or unpolarized?
a. If it is polarized, the electric field vibrates in only one plane. If light isn't polarized, the electric field is free to vibrate any which way it likes.
mostly correct
Horizontally Polarized LightHorizontally Polarized Light
Credit: the next few slides are from Dr. Durfee
Vertically Polarized LightVertically Polarized Light
Diagonally Polarized LightDiagonally Polarized Light
Circularly Polarized LightCircularly Polarized Light
Elliptically Polarized LightElliptically Polarized Light
Unpolarized LightUnpolarized Light
Clicker question: What type of polarization is displayed in
the animation? http://stokes.byu.edu/teaching_resources/emwave_flash.html
a. Horizontally polarizedb. Vertically polarizedc. Diagonally polarizedd. Circularly polarizede. Non-polarized
Circularly Polarized, pictures
Pictures from Wikipedia
Polarizers Lines of wires Polaroid Film Crystals
Polaroid film Crystals
www.thorlabs.com
Clicker question: If you send horizontal linearly polarized
light through a (perfect) vertical polarizer, how much of the light intensity will get through?
a. 0-20%b. 20-40%c. 40-60%d. 60-80%e. 80-100%
Clicker question: If you send horizontal linearly polarized
light at 45 through a perfect vertical polarizer, how much of the light intensity will get through?
a. 0-20%b. 20-40%c. 40-60%d. 60-80%e. 80-100%
Clicker question: If you send circularly polarized light
through a perfect vertical polarizer, how much of the light intensity will get through?
a. 0-20%b. 20-40%c. 40-60%d. 60-80%e. 80-100%
Clicker question: (Like HW 27-2) If you send horizontal linearly
polarized light through a vertical polarizer, no light gets through because there is no component of the electric field in the light wave that is oscillating vertically. If you insert a diagonal polarizer at 45 between the two, how much of the light intensity will now get through the final polarizer?
a. 0-20%b. 20-40%c. 40-60%d. 60-80%e. 80-100%
Demos Polarization configurations
From warmup:
In the discussion accompanying the figure shown above, the text explains how a certain reflection angle can lead to polarization. In your own words, explain how this works.
a. When waves are reflected off of surfaces, the parallel [to the surface] component reflects more strongly than the perpendicular [to the first component] component.
b. At a certain angle, the only light that reflects must be oriented parallel to the surface. Kind of like how a flat, horizontal rock is the best to skip across water.
Remember these? (Fresnel Coefficients)
2 1 1 2
1 2 1 2
v v n nrv v n n
2 1
1 2 1 2
2 2v ntv v n n
If near perpendicular (1-D problem)
2R r 2
1T r
For arbitrary angle (you don’t need to know for this class)
1 1 2 2.
1 1 2 2
cos cos
cos coss polarn n
rn n
1 2 2 1.
1 2 2 1
cos cos
cos cosp polarn n
rn n
1 1.
1 1 2 2
2 cos
cos coss polarn
tn n
1 1.
1 2 2 1
2 cos
cos cosp polarn
tn n
What is s-polar? What is p-polar?
When/what is phase shift?
Plots for air (n=1) to glass (n=1.5)s-polarization p-polarization
field amplitudes vs
intensities vs
20 40 60 80
1.0
0.5
0.5
r
t
20 40 60 80
0.2
0.4
0.6
0.8
1.0
R
T
20 40 60 80 0.2
0.2
0.4
0.6
0.8
1.0
r
t
20 40 60 80
0.2
0.4
0.6
0.8
1.0
R
T
field amplitudes vs
intensities vs Brewster’s angle!Do you always get a
180 phase shift upon reflection?
Fresnel Coefficients, cont.
2 1 1 2
1 2 1 2
v v n nrv v n n
2 1
1 2 1 2
2 2v ntv v n n
If near perpendicular (1-D problem)
2R r 2
1T r
For arbitrary angle (you don’t need to know for this class)
1 1 2 2.
1 1 2 2
cos cos
cos coss polarn n
rn n
1 2 2 1.
1 2 2 1
cos cos
cos cosp polarn n
rn n
1 1.
1 1 2 2
2 cos
cos coss polarn
tn n
1 1.
1 2 2 1
2 cos
cos cosp polarn
tn n
Set numerator = 0, apply Snell’s Law… a bit of algebra/trig…
tan1 = n2/n1
Clicker question:
If you send an unpolarized beam at a piece of glass at Brewster’s angle, what happens?
a. The reflected beam is partially polarizedb. The reflected beam is completely polarizedc. The transmitted beam is partially polarizedd. The transmitted beam is completely
polarizede. More than one of the above
“Brewster windows”
If you send p-polarized light towards a piece of glass at Brewster’s angle, how much gets transmitted?
20 40 60 80 0.2
0.2
0.4
0.6
0.8
1.0
r
t
20 40 60 80
0.2
0.4
0.6
0.8
1.0
R
T
p-polarization
Clicker question:
In polarized sunglasses, some of the glare from the sun is eliminated when the sun is directly in front (and above) you. Should the polarizing material be aligned to allow vertical or horizontal electric fields through?
a. verticalb. horizontal
Demo
Flashlight reflecting off of glass