- Fabry-Perot interferometer
A multiple-beam interferometer, usually consisting of two flat plates, with high reflective ability. The plates are set parallel to one another by spacers so that lightwaves may bounce back and forth between them several times. The requirements for constructive interference of reflected lightwaves of a given wavelength can be fulfilled only at particular angles, relative to the normal to the plates. Therefore, Fabry-Perot interferometers can be used as spectrometers with high resolution. Used as a laser resonator, the Fabry-Perot reinforces only light of specific frequencies traveling perpendicular to the mirror surfaces, and its successive reflections and amplifications form the oscillating mode.