Brewster windows are typically used as polarizers within laser cavities. When positioned at Brewster’s angle (55° 32′ at 633 nm), the P-polarized portion of the light will pass through the window with no losses, while a fraction of the S-polarized portion will be reflected off the Brewster window. When used in a laser cavity, the Brewster window essentially acts as a polarizer.
Brewster’s angle is given by
tan(θB) = nt/ni
θB is Brewster’s angle
ni is the index of refraction of the incident medium, which is 1.0003 for air
nt is the index of refraction of the transmitting medium, which is 1.45701 for fused silica at 633 nm
Paralight Optics offers Brewster windows are fabricated from N-BK7 (Grade A) or UV fused silica, which exhibits virtually no laser-induced fluorescence (as measured at 193 nm), making it an ideal choice for applications from the UV to the near IR. Please see the following Graph showing reflectance for both S- and P-polarization through UV fused silica at 633 nm for your references.
N-BK7 or UV Fused Silica Substrate
High Damage Threshold (Uncoated)
Zero Reflection loss for P-Polarization, 20% Reflection for S-Polarization
Ideal for Laser Cavities
The reference drawing to the left shows the reflection of S-polarized light and transmission of P-polarized light through a Brewster window. Some S-polarized light will be transmitted through the window.
Substrate Material
N-BK7 (Grade A), UV fused silica
Type
Flat or Wedged Laser Window (round, square, etc.)
Size
Custom-made
Size Tolerance
Typical: +0.00/-0.20mm | Precision: +0.00/-0.10mm
Thickness
Custom-made
Thickness Tolerance
Typical: +/-0.20mm | Precision: +/-0.10mm
Clear Aperture
> 90%
Parallelism
Precision: ≤10 arcsec | High Precision: ≤5 arcsec
Surface Quality (Scratch - Dig)
Precision: 60 - 40 | High Precision: 20-10
Surface Flatness @ 633 nm
Precision: ≤ λ/10 | High precision: ≤ λ/20
Transmitted Wavefront Error
≤ λ/10 @ 632.8 nm
Chamfer
Protected: < 0.5mm x 45°
Coating
Uncoated
Wavelength Ranges
185 - 2100 nm
Laser Damage Threshold
>20 J/cm2 (20ns, 20Hz, @1064nm)
♦ The graph to the right shows the calculated reflectance of uncoated UV fused silica for polarized light at various angles of incidence (The reflectance for P-polarized light goes to zero at Brewster's angle).
♦ The index of refraction of UV fused silica varies with wavelength shown in the following left-hand graph (the calculated index of refraction of UV fused silica as a function of wavelength from 200 nm to 2.2 μm).
♦ The following right-hand graph shows the calculated value of θB (Brewster's angle) as a function of wavelength from 200 nm to 2.2 μm when light is passing from air to UV fused silica.