optics Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of optical instruments, instruments that use or Photodetector, detect it. Optics usually describes t ...

, a Littrow prism, or Littrow mirror, originally part of a Littrow spectrograph (after

Otto von Littrow Otto von Littrow (14 February 1843, Vienna – 7 November 1864, Vienna) was an Austrian astronomer and physicist. He is known for his contributions in spectrometer instrumentation. Son of astronomer Karl L. Littrow and women's movement leader Au ...

), is a retro-reflecting, dispersing prism arranged in such a way that an incident light beam which enters at the

Brewster angle Brewster's angle (also known as the polarization angle) is an angle of incidence at which light with a particular polarization is perfectly transmitted through a transparent dielectric surface, with ''no reflection''. When ''unpolarized'' ligh ...

undergoes minimal deviation and hence maximum dispersion.

Description

Littrow (optical) prisms typically have the shape of a (geometric) prism with a 30°/60°/90° right triangular base, equivalent to half an

equilateral triangle An equilateral triangle is a triangle in which all three sides have the same length, and all three angles are equal. Because of these properties, the equilateral triangle is a regular polygon, occasionally known as the regular triangle. It is the ...

. Typically, they are coated with a reflective film coating on the surface opposite the 60° angle. This design was devised by

(1843–1864).

Applications

Typically Littrow prisms are used in

laser A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word ''laser'' originated as an acronym for light amplification by stimulated emission of radi ...

s at the end of an

optical cavity An optical cavity, resonating cavity or optical resonator is an arrangement of mirrors or other optical elements that confines light waves similarly to how a cavity resonator confines microwaves. Optical cavities are a major component of lasers, ...

to offer fine adjustment of the laser's output frequency by altering the angle of incidence. Before the ready availability of

diffraction grating In optics, a diffraction grating is an optical grating with a periodic structure that diffraction, diffracts light, or another type of electromagnetic radiation, into several beams traveling in different directions (i.e., different diffractio ...

s Littrow prisms were used widely in

spectroscopy Spectroscopy is the field of study that measures and interprets electromagnetic spectra. In narrower contexts, spectroscopy is the precise study of color as generalized from visible light to all bands of the electromagnetic spectrum. Spectro ...

. They are still used in some UV instruments and in one section of some specialized double monochromators.

References

{{reflist Prisms (optics)