Littrow Dispersion Prism

Also known as a 30-60-90 dispersion prism, it is available in two versions: uncoated and coated. An uncoated Littrow dispersion prism disperses white light into its spectral components, similar to an equilateral prism; a coated Littrow dispersion prism deviates the ray path by 60° without inverting or reverting the image. The hypotenuse of the coated version is at Brewster's angle for 514.5nm, resulting in retroreflection at that wavelength. Rotating the prism changes the retroreflected wavelength and makes this prism suitable for line selection in a laser.