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