If you're directing the beam "through the glass" (by the looks of it from the diagram) you'll get more losses. (e.g. BK7 > SF2 etc.) [Anamorphic prism losses sound familiar?]
Why not aim onto the hypotenuse (input = west) (with an AR coating spec'd for 45 deg AOI) and output = north?
This will reduce you losses by quite a large margin.
I can't honestly think of reason why you'd want to have that optic used as a pure prism, rather than a 45deg mirror.
Lasertack sell these prism mirrors in his shop if you need to test them.
- There is no such word as "can't" -
- 60% of the time it works every time -