# Brewster's Angle

When Sir David Brewster was studying Polarization he found that at a certain angle the reflected light was completely polarized. We now call this light s-polarized. The p-polarized light is completely transmitted throught the medium.

As holographers we use this method to polarize lasers by inserting a brewster's window into a laser or to minimize the reflections from a piece of glass holding our emulsion.

Since out laser is completely polarized we can choose s or p polarization independently from the other.

A graph of reflection vs incedent angle for s-polarized (dashed Line) light and p-polarized (solid line) light.

### Brewster's Law

Brewster's Law calculates the angle of minimum reflection for p-polarized light. n1 and n2 are the refractive indicies of the two media. Usually for us that is 1 for air and about 1.5 for glass.

So, for air at 1.00029 and glass at 1.5 we get:

tan(theta)=1.5/1.00029

theta=56.3deg

And then for gelatin 1.36:

tan(theta)=1.36/1.00029

theta=53.66deg