Equilateral optical prism
CVI Melles Griot
Equilateral dispersing prisms are used for wavelength-separation applications. A light ray is twice refracted passing through the prism with total deviation denoted by θd in the figure below. Deviation is a function of refractive index and hence wavelength. Angular dispersion Δθd is the difference in deviation for light rays having different wavelengths, and it varies with prism orientation.
Reflection losses are minimized for unpolarized rays traveling parallel to the base of the prism. This condition is called minimum deviation.
Minimum deviation occurs when the ray and wavelength angle of incidence at the entrance surface are equal to the angle of emergence (both angles measured with respect to the surface normals).
Prisms are available in N-BK7, N-F2 and N-SF10 glass as well as UV-grade fused silica.
Antireflection coatings help reduce polarization at the prism surfaces by increasing total transmittance.