1. Trivia Question
Human vision (in daylight) is based on three color receptors which are sensitive to Red, Green, and Blue light. Hence RGB monitors… How many colors can the Mantis Shrimp see?
Zero – they are blind
2 – Black and White
(c) 3
(d) 6
(e) 12

2. Trivia Question
Human vision (in daylight) is based on three color receptors which are sensitive to Red, Green, and Blue light. Hence RGB monitors… How many colors can the Mantis Shrimp see? (e) 12
The mantis shrimp also has the fastest punch in the animal kingdom…. The speed of a 22 caliber bullet….
The motion of punch is so fast, that it leaves open cavities (ie. no water) behind the punch.

3. Lorentz Model
Solve F=ma in the presence of polarizability of a material.
RESULTS:
Refractive index depends on wavelength (dispersion)
Absorption also depends on wavelength (why some materials are different colors)
Refractive index is not only complex, but also can be less than 1!

4. Polarizability of BOUND electronic charges
Since positive charge (with all protons) is so much heavier than negative charges (electrons), consider positive charge to be fixed and only negative ‘cloud’ of electrons move.
# of electrons
Per unit volume
Charge of electron

5. Polarizability of BOUND electronic charges
Frictional ‘drag’
term
Restoring force by induced separation of charges
Force on electrons by E field of light wave
Charge of electron

6. Hooke’s Law Mechanical Analog
Mass on spring oscillates with a RESONANT frequency of
khooke m

7. Real and Imaginary Index
fj is the “oscillator” strength
NOTE:
Regions of frequency where there is HIGH absorption leads to a RAPIDLY changing real index.
Where there is little absorption, real index roughly constant.
Real index can be less than 1!

8. What if there are SEVERAL resonant frequencies?

9. “free” electrons moving in E Field

10. Dispersion model for Metal
Note: for Electromagnetic frequencies below plasma frequencies,
And imaginary refractive index LARGE.
For frequencies above plasma frequency,
And real refractive index approaches UNITY.
For electromagnetic frequencies BELOW the plasma frequency, the light is highly reflected… for example, visible light from a silvered mirror.
For x-rays, the frequency is HIGH ABOVE, the plasma frequency, and x-rays pass through silvered mirror.

11. Basics of Metamaterials
If ε > 0, and μ > 0, take POSITIVE square root.
If ε < 0, and μ < 0, simultaneously, take NEGATIVE square root.

12. Negative Refractive Index Materials
‘Cloaking’ devices
Snell’s Law with negative refractive index… so called ‘Left Handed Materials’

13. Focusing and Absorbing example
You can also design metamaterials which are perfect absorbing material (in a spectral range) …. Good for stealth technology. Energy from radar absorbed rather than reflected.

14. Negative Refractive Index Materials
Time Averaged Poynting Vector is ANTIPARALLEL to phase velocity.
E, B, and k follow a LEFT HANDED rule E E k B k B
Negative Refractive Index wave
Right-handed ‘NORMAL’ wave

15. What do metamaterials look like?
Size of individual structures SMALLER than wavelength of electromagnetic radiation
Microwave range – combination of metallic split rings (for magnetic permeability control) and metallic lines (for permittivity E field controll)

16. Subwavelength Structures – Photonic Crystal
Light out
Pillars of GaAs
Light in
wavelength

17. Other methods of ‘cloaking’

18. Primary Colors Red Green Blue - RGB
Primary color set NOT unique. Typically use RGB since these are the phosphors used to generate colors in TV sets/ monitors. RGB also correspond (roughly) to the photoreceptors in the human eye
James Clerk Maxwell

19. ADDITIVE combinations of RGB
If we MIX blue, green, and red pigments like the ones illustrated here, what color is the TOTAL reflected light?

20. Human Detection of Light
Two types of color receptors in the human eye
Rods (best for dim light – Scotopic Vision)
Cones (best for bright light – Phototopic Vision)
Responsivity
Normalized responsivity spectra of human cone cells, S (short), M (medium), and L (long) types
Rod sensitivity compared to Cones

21. Luminous Power
Luminous power – ‘correction’ for detection efficiency of eye
Responsivity (Lumens)
1W = 683

22. SUBTRACTIVE combinations (ie. Transmission)
STARTING with WHITE light, REMOVE the blue color (by absorbing blue) and the resulting color appears as yellow (combination of Red and Green)

23. Additive vs Subtractive Colors
Subtractive color systems start with white light. Colored inks, paints, or filters ABSORB some of the white light, giving the reflected light color. Useful to think of transmission THROUGH color filter with some colors ABSORBED.
Conversely, additive color systems start with darkness. Various colors are ADDED together to produce a range of colors. Useful to think of REFLECTION from additive color systems. MIXING colors means that BOTH colors are together in reflection.
RGB
cyan, magenta and yellow (CMY)
Complimentary colors – Absence (subtraction or absorption) of green light from ‘white’ light gives purple (magenta).
Eg. Amount of printed magenta ink determines how much green light is absorbed (not reflected) from page

24. Transmission colors
Overall transmission is the MULTIPLICATION or product of individual multiplications

25. Trivia Question
Human vision (in daylight) is based on three color receptors which are sensitive to Red, Green, and Blue light. Hence RGB monitors… How many colors can the Mantis Shrimp see? (e) 12
The mantis shrimp also has the fastest punch in the animal kingdom…. The speed of a 22 caliber bullet….
The motion of punch is so fast, that it leaves open cavities (ie. no water) behind the punch.

26. Scattering Reason for white fog/ clouds
Scattering independent of color
Reason for Blue Sky/ Red sunsets - Scattering ~ 1/λ4

27. Color from Scattering
Opal structures – (interference from scattered light from small structures)