Rocky Mountain Instrument Co.

Optical Components:

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Windows » IR Brewster Windows

Brewster Windows are primarily used in laser cavities to produce a beam with a high degree of polarization purity. When unpolarized light is incident on an uncoated substrate at Brewster’s Angle, the reflected portion is completely S polarized and the transmitted portion is partially P polarized. Multiple passes through the substrate substantially reduces the S component in the transmitted beam, resulting in a highly P polarized output. Multi-layer Thin Film Polarizer coatings can be applied to these substrates to greatly improve efficiency and extinction ratio on a single pass through the substrate.

Brewster windows are an economical option for coupling linearly polarized light into sealed optical systems and to select the polarization of light traveling in optical cavities.

Brewster's angle can be calculated using the following equation:


Where θB is Brewster's angle and nw and na are the indices of refraction for the window and the ambient respectively. na is usually assumed to be 1 for air.

RMI Standard Specifications
Materials: ZnSe, Ge, Chalcogenide glass
Angle of Incidence:
Ge, Chalcogenide glass:
Brewster's Angle (θΒ)
67.4º at 10.6 µm
76.0º at 10.6 µm
Surface Figure:
ZnSe, Ge, Chalcogenide glass:
Both Surfaces
λ/20 at 10.6 µm
Surface Quality:
ZnSe, Ge, Chalcogenide glass:
Both Surfaces
Dimensional Tolerance: + 0.000", – 0.010"
Thickness Tolerance: ± 0.010"
Wedge: ≤ 3 arc minute
Bevels: 0.02" at 45º typical
Clear Aperture: Central 85% of diameter