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. a.polarization by reflection (3 students) Other comments? a. 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. 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 Light Credit: the next few slides are from Dr. Durfee
Vertically Polarized Light
Diagonally Polarized Light
Circularly Polarized Light
Elliptically Polarized Light
Unpolarized Light
Clicker question: What type of polarization is displayed in the animation? a. a.Horizontally polarized b. b.Vertically polarized c. c.Diagonally polarized d. d.Circularly polarized e. e.Non-polarized
Circularly Polarized, pictures Pictures from Wikipedia
Polarizers Lines of wires Polaroid Film Crystals Polaroid film Crystals
Clicker question: If you send horizontal linearly polarized light through a (perfect) vertical polarizer, how much of the light intensity will get through? a. a.0-20% b. b.20-40% c. c.40-60% d. d.60-80% e. e %
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. a.0-20% b. b.20-40% c. c.40-60% d. d.60-80% e. e %
Clicker question: If you send circularly polarized light through a perfect vertical polarizer, how much of the light intensity will get through? a. a.0-20% b. b.20-40% c. c.40-60% d. d.60-80% e. e %
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. a.0-20% b. b.20-40% c. c.40-60% d. d.60-80% e. e %
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. 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. 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) If near perpendicular (1-D problem) For arbitrary angle (you don’t need to know for this class) What is s-polar? What is p-polar? When/what is phase shift?
Plots for air (n=1) to glass (n=1.5) s-polarizationp-polarization field amplitudes vs intensities vs r t R T r t R T field amplitudes vs intensities vs Brewster’s angle! Do you always get a 180 phase shift upon reflection?
Fresnel Coefficients, cont. If near perpendicular (1-D problem) For arbitrary angle (you don’t need to know for this class) Set numerator = 0, apply Snell’s Law… a bit of algebra/trig… tan 1 = n 2 /n 1
Clicker question: If you send an unpolarized beam at a piece of glass at Brewster’s angle, what happens? a. a.The reflected beam is partially polarized b. b.The reflected beam is completely polarized c. c.The transmitted beam is partially polarized d. d.The transmitted beam is completely polarized e. e.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? r t 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. a.vertical b. b.horizontal
Demo Flashlight reflecting off of glass