Optics: Design of Beamsplitter Ge on KBr substrate

[SupaVillain]

Hi there, I am making a beam splitter for an FTIR, but I do not know the anatomy of a beamsplitter of this type, does anybody have information on the design of these?

I plan to order KBr crystal windows and apply the Ge coating myself using physical vapor deposition and assuring quality with a calo tester. I just don't know how thick i need it and how i get it to actually split the HeNe laser

 

[reasonableman]

I think you are just essentially solving Fresnel's equations. If you're looking at thin films wikipedia suggests the transfer matrix method.

http://en.wikipedia.org/wiki/Transfer-matrix_method_(optics)