2. Announcements
See on exam results and scoring. Will return at end of class.

3. Reading Quiz Which quantities can be greater than c? a) vphase
b) signal propagation speeds
c) image propagation speeds

4. Reading Quiz Group velocity is given by (you can check units) a. b. c.

5. Ellipsometry: finding n, k or thicknesses, roughness…3
starts linear, angle a
linear polarizer, angle q 1 2
does something
Wikipedia

6. Superposition of Waves
Single frequency light has infinite extent in time (mathematical, not physical)
Any light with information (e.g. pulsing) has to contain a spread in frequencies.
Any light created in the universe has more than one frequency (it had a beginning).

7. Superposition of Waves
Addition of two waves, equal magnitude:

8. Superposition of Waves
Phase velocity
speed of single frequency wave
Group velocity
(this definition not valid when absorption is strong)
speed of “envelope”, pulse, signal, image, energy, information

9. Dispersion due to n(w) Wave speed depends on w
kRe (w)=n(w) w/c
Dispersion: when vphase is not constant: k(w) and w(k) are not linear:
vphase =c/n(w) n w

10. Does group velocity exceed c?
kRe (w)=n(w) w/c
k/w =1/c
Look at slope for vg :
Where our definition is valid (low absorption), w

11. “Things” that go faster than the speed of light
Waves on beach move at v<c (duh)
The point on the beach that is getting hit moves to the left at v/sin(q), which could be anything greater than v. But that speed is a mathematical thing, not a physical one.

12. If in some strange system,
then the group velocity is

13. If in some strange system, the group velocity is

14. Energy and superimposed plane waves
Practicing simple addition of waves (Phscs 123)
You add two waves, of amplitude E1 and 2E1. Same polarization. In some places they add constructively, and some places destructively. E1 by itself corresponds to intensity I1 .
The brightest intensities seen in the interference pattern are:
3I1
4I1
6I1
9I1
25I1

15. You add two coherent 1-D waves, of intensities I1 and 9I1
You add two coherent 1-D waves, of intensities I1 and 9I1. In some places they add constructively, and some places destructively.
The dimmest intensities seen in the interference pattern are:
2I1
3I1
4I1
6I1
8I1

16. We can write
Find in terms of
I did it
I tried

18. What color(s) do the surfaces of these red plastic objects reflect?

19. From an optics perspective, what’s the biggest difference between what’s inside the two red plastics?

21. Interference/diffraction (“structural”) colors in nature: iridescence

22. Opals are natural 3-d diffraction gratings or “photonic crystals”

25. What’s missing in the albino peacock?

26. Opals

27. Photonic Crystals: 3-D diffraction grating

28. Nocturnal animals
have layer of cells behind retina with multilayer mirrors that reflect unabsorbed light back through it!

30. Cameleon

31. Change colors for camouflage, mood
Outer layer: cells that can concentrate red or yellow pigment in center (cells almost clear), or spread them over cell (colored)
Middle layer: sacks of photonic crystal plates, reflecting blue
Inner layer: cells that can concentrate melanin (black) in center (cells almost clear), or spread them over cell (black)
Only 1 and 3 controlled by nerves?

32. Chromatophore organ

33. Iridophores (photonic crystals) and chromatophores (pigment organs)

34. Chameleon colours 'switched by crystals' - http://www. bbc. co
Latest
Chameleon colours 'switched by crystals' -