The window cutted as brewster angle, It's used as polarizer in laser cavity.    

Brewster Windows are uncoated substrates which are used as polorizers, typically within a laser cavity. Positioned at Brewster's Angle the P-Polarization portion of the light will pass through the window with no losses while the S Polarization portion will be reflected off the brewster window. Used in a laser cavity the brewster window is essentially a polorizer.     

Brewster's Angle is calculated from:    

 θ= tan-1(n)    

 where θ is Brewster's Angle and n is the refraction index of the material.     

Material: BK7 or Fused silica     

Specifications:    

Diameter Tolerance: +0.0, -0.1mm     

Thickness Tolerance: ± 0.2mm    

Clear Aperture: >85%   

Surface Quality: 10-5 scratch and dig      

Wavefront transmission: λ/10 @632.8nm    

Parallelism: <5 arc seconds   

Protective Bevel