Optics Questions

Unanswered

• Is it possible for a substance to allow more light through one direction than the opposite direction? Maybe, Feynman page II-24-10 says that unidirectional couplers can do this. But wouldn't it violate the 2nd Law of Thermodynamics if you had reservoirs at each end with equal temperatures, the blackbody radiation would only be passed through in one direction, which would cool off one side. I don't know if we could say it is a parity violation of the EM interaction because the matter itself may not be parity symmetric.
• Is it possible to cause two lasers to interfere in such a way that the frequency changes?

Answered

• Why are red, yellow, and blue considered primary colors when red, green, and blue are the additive primaries and cyan, magenta, and yellow are the subtractive primaries? Red-Yellow-Blue is just an approximation to the subtractive primaries because red is more common than magenta and blue is more common than cyan.
• What is the difference between a white surface and a mirror? The white surface is bumpy while the mirror is smooth.