I used this illustration because this is the objective eye piece I used for the inner chamber of the collimation tube

The graph below is the angle of incidence for the "brewster" angle for the 1st sapphire wndow:

These parts have been uploaded as STL (mesh) files added to the components section, this is a critical piece of instrumentation, as the laser beam needs to be squeezed in very tightly and very precisely. The 2 sapphire windows, provide this accuracy and transmission, with no reflective aberrations occurring in the inner chamber.