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Huygen’s Principle Each wavefront serves as source of spherical waves HW 26-5 (extra credit): a. a.“Stare at the picture until you can visualize that the green lines tangent to the circles connect matching wavefronts.” b. 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: Wikipedia Double-slit_experiment

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 What type of polarization is displayed in the animation? a. a.Horizontally polarized b. b.Vertically polarized c. c.Diagonally polarized d. d.Other polarized e. e.Non-polarized

Circularly Polarized, pictures Pictures from Wikipedia

Polarizers Lines of wires Polaroid Film Crystals Polaroid film Crystals

Thought 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 %

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. a.0-20% b. b.20-40% c. c.40-60% d. d.60-80% e. e %

Thought 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 %

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. a.0-20% b. b.20-40% c. c.40-60% d. d.60-80% e. e %

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. a.Brewster’s Angle b. b.Euler’s Angle c. c.Maxwell’s Angle d. d.Snell’s Angle e. e.Sorenson’s Angle

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?

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… lots of algebra/trig… tan  1 = n 2 /n 1

Thought 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 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. a.Why are metals better reflectors than insulators are? b. b.What is the emitted light from an oscillating electron? Brewster’s angle: reflected ray at 90  to transmitted ray a. a.What happens to p-polarization at this angle?