The prisms are made of fused silica (Homosil) and consist of two identical cemented prisms The angles of these prisms are 30° - 60° - 90°. The long cathetus of one of the prisms is coated with a partially reflecting protected silver layer for the visible spectral range.

A Kösters prisms generates two parallel output beams. It allows a simple realization of a white light interferometer having exactly equal optical length in both arms.

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