Announcements 3/9/11 Prayer Test going on…. Huygen’s Principle Each wavefront serves as source of spherical waves HW 26-5 (extra credit): a. a.“Stare.

Announcements 3/9/11 Prayer Test going on…

Huygen’s Principle

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

Image credit: Wikipedia

Huygen’s Principle, cont.

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

Image credit: Wikipediahttp://en.wikipedia.org/wiki/

Double-slit_experiment

Spherical WavesSpherical Waves

Credit: the next few slides are from Dr. Durfee

Huygen’s Construction of a Spherical Huygen’s Construction of a Spherical WaveWave

Huygen’s Construction of a Plane WaveHuygen’s Construction of a Plane Wave

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

Thought question What type of polarization is displayed in

the animation? http://stokes.byu.edu/emwave_flash.html

a. Horizontally polarizedb. Vertically polarizedc. Diagonally polarizedd. Other polarizede. Non-polarized

Circularly Polarized, pictures

Pictures from Wikipedia

Polarizers Lines of wires Polaroid Film Crystals

Polaroid film Crystals

www.thorlabs.com

Thought 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%

Thought 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%

Thought 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%

Thought 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

Reading Quiz What do we call the angle at which light,

reflected off of a (non-conducting) surface, is completely polarized?

a. Brewster’s Angleb. Euler’s Anglec. Maxwell’s Angled. Snell’s Anglee. Sorenson’s Angle

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?

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… lots of algebra/trig…

tan1 = n2/n1

Thought 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

Applications:Sunglasses

Laser “Brewster windows”

Brewster’s angle

Why does the light “care” about 90?

Image from Wikipedia

Reflection: microscopic details 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?