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

, a Littrow prism or Littrow spectrograph or Littrow mirror is a retro-reflecting

dispersing prism In optics, a dispersive prism is an optical prism that is used to disperse light, that is, to separate light into its spectral components (the colors of the rainbow). Different wavelengths (colors) of light will be deflected by the prism at di ...

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. Littrow prisms are typically 30°/60°/90° prisms, with a reflective film coating on the surface opposite the 60° angle. It was devised by

Otto von Littrow Otto is a masculine German given name and a surname. It originates as an Old High German short form (variants ''Audo'', ''Odo'', ''Udo'') of Germanic names beginning in ''aud-'', an element meaning "wealth, prosperity". The name is recorded fr ...

(1843—1864). 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" is an acronym for "light amplification by stimulated emission of radiation". The firs ...

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 forms a cavity resonator for light waves. Optical cavities are a major component of lasers, surrounding the gain medium and pro ...

to offer fine adjustment of the laser's output frequency by altering the

angle of incidence Angle of incidence is a measure of deviation of something from "straight on" and may refer to: * Angle of incidence (aerodynamics), angle between a wing chord and the longitudinal axis, as distinct from angle of attack In fluid dynamics, ang ...

. Before the ready availability of

diffraction grating In optics, a diffraction grating is an optical component with a periodic structure that diffracts light into several beams travelling in different directions (i.e., different diffraction angles). The emerging coloration is a form of structural ...

s Littrow prisms were used widely in

spectroscopy Spectroscopy is the field of study that measures and interprets the electromagnetic spectra that result from the interaction between electromagnetic radiation and matter as a function of the wavelength or frequency of the radiation. Matter ...

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

References

{{reflist Prisms (optics)