The window thickness required to withstand pressure differential at opposite sides can be calculated by the following equation:
Thk = √( 1.1 x P x r² x SF/MR),
P = Pressure difference (PSI),
r = Unsupported radius (mm),
SF = Safety factor (4 to 6) (suggested range, may use other factors),
MR = Modulus of rupture (PSI).
For example, Ge window with diameter 100 mm and unsupported radius 45 mm used in environment with pressure differential of 1 atmosphere should have thickness of ~4.0 mm (safety factor 5).