Hi guys, I am interested in designing a chamber that is either purged with nitrogen gas or vacuum sealed that encloses a thin film sample. The method of analysis is via ellipsometry. (My knowledge of optics is extremely limited but know that ellipsometry measures some shift in polarization of light upon reflection off a surface to determine thickness of film). The most immediate problem for me is determining what material to make the viewing ports for which the incident ray can pass through readily and keep all its properties (good transmittance, no changes in polarization, etc) and what the angle of the ports should be at (we normally do measurements at 65 degrees; so to eliminate refractance due to material, I've figured it should be placed at a 65 degree angle. Are there other factors that I should consider? Thanks.