Announcements 3/9/11
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Prayer
Test going on…
Huygen’s Principle
Image credit: Wikipedia
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Each wavefront serves as source of spherical waves
HW 26-5 (extra credit):
a. “Stare at the picture until you can visualize that the green lines
tangent to the circles connect matching wavefronts.”
b. Construct an accurate picture like this for a specific situation,
show graphically that it gives you Snell’s law
Huygen’s Principle, cont.
Image credit: Wikipedia
http://en.wikipedia.org/wiki/
Double-slit_experiment
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A wave hits the two slits
Each slit (infinitely narrow) becomes source of spherical
waves
The waves from those two sources interfere with each
other
Spherical Waves
Credit: the next few slides are from Dr. Durfee
Huygen’s Construction of a Spherical Wave
Huygen’s Construction of a Plane Wave
Horizontally Polarized Light
Credit: the next few slides are from Dr. Durfee
Vertically Polarized Light
Diagonally Polarized Light
Circularly Polarized Light
Elliptically Polarized Light
Unpolarized Light
Thought question
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What type of polarization is displayed in the
animation?
http://stokes.byu.edu/emwave_flash.html
a. Horizontally polarized
b. Vertically polarized
c. Diagonally polarized
d. Other polarized
e. Non-polarized
Circularly Polarized, pictures
Pictures from Wikipedia
Polarizers
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Crystals
Lines
Polaroid
of wires
film
Polaroid Film
Crystals
www.thorlabs.com
Thought question
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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%
Thought question
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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%
Thought question
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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%
Thought question
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(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
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Polarization configurations
Reading Quiz
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What do we call the angle at which light,
reflected off of a (non-conducting) surface, is
completely polarized?
a. Brewster’s Angle
b. Euler’s Angle
c. Maxwell’s Angle
d. Snell’s Angle
e. Sorenson’s Angle
Remember these? (Fresnel Coefficients)
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If near perpendicular (1-D problem)
v2  v1 n1  n2
r

v1  v2 n1  n2
R r
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2v2
2n1
t

v1  v2 n1  n2
2
T  1 r
2
For arbitrary angle (you don’t need to know for this class)
n1 cos1  n2 cos2
rs polar . 
n1 cos1  n2 cos2
ts polar . 
n1 cos2  n2 cos1
rp polar. 
n1 cos2  n2 cos1
2n1 cos1
t p polar. 
n1 cos2  n2 cos1
2n1 cos1
n1 cos1  n2 cos2
What is s-polar? What is p-polar?
Plots for air (n=1) to glass (n=1.5)
s-polarization
p-polarization
field amplitudes vs 
field amplitudes vs 
1.0
t
0.5
t
0.8
0.6
20
40
60
80
r
0.5
0.4
r
0.2
20
1.0
40
60
80
0.2
intensities vs 
Do you always intensities
get a
180 phase shift1.0upon
reflection?0.8
1.0
T
0.8
0.6
0.6
0.4
0.4
R
0.2
20
40
vs 
T
R
0.2
60
80
Brewster’s angle!
20
40
60
80
Fresnel Coefficients, cont.
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If near perpendicular (1-D problem)
v2  v1 n1  n2
r

v1  v2 n1  n2
R r

2v2
2n1
t

v1  v2 n1  n2
2
T  1 r
2
For arbitrary angle (you don’t need to know for this class)
n1 cos1  n2 cos2
rs polar . 
n1 cos1  n2 cos2
ts polar . 
2n1 cos1
n1 cos1  n2 cos2
n1 cos2  n2 cos1
2n1 cos1
rp polar. 
t p polar. 
= 0,
apply Snell’s Law…
n1 cos2  n2 cos1 Set numerator n
1 cos 2  n2 cos1
lots of algebra/trig…
tan1 = n2/n1
Thought question
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If you send an unpolarized beam at a piece of glass
at Brewster’s angle, what happens?
a. The reflected beam is partially polarized
b. The reflected beam is completely polarized
c. The transmitted beam is partially polarized
d. The transmitted beam is completely polarized
e. More than one of the above
Applications:
Sunglasses
Laser “Brewster windows”
Brewster’s angle
Image from
Wikipedia
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Why does the light “care” about 90?
Reflection: microscopic details
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How does the wire-line polarizer work?
Reflection off of a surface
a. Why are metals better reflectors than
insulators are?
b. What is the emitted light from an oscillating
electron?
Brewster’s angle: reflected ray at 90 to
transmitted ray
a. What happens to p-polarization at this angle?