7. Fresnel Reflection

Written by Scott Sparrold

Ever stand in front of a window and see your yourself as well as the scene on the other side? The scene on the other side is transmission and your image is reflection.

A ray that enters another optical medium at normal incidence (0° angle of incidence) a small percentage of light will be reflected back upon itself:

n1 = initial optical medium's index of refraction
n2 = the optical medium's index of refraction

Transmissions is easily calculated:
T = 1 - R

Side notes:
This equation is intended to show how glass will reflect a little bit of energy. All material's index of refraction really has two components: a real and an imaginary part (square root of -1). Glass has a very small imaginary part. Metals have  a very large imaginary part. The reflection coefficient calculated above shows only the real part. When calculating reflection for a mirror, one has to include the imaginary part and the reflection coefficient is very high.... which is why metals reflect while glasses transmit.

Hurry up Scotty and show us how to reduce the imaginary part of aluminums index of refraction, so we can get transparent aluminum (yes another Star Trek reference)