FabryPérotCavity

A Fabry-Pérot cavity, also known as an optical cavity or etalon, is an optical resonator formed by two parallel mirrors. Light introduced into the cavity is reflected back and forth between the mirrors. At specific wavelengths, the light constructively interferes, creating a standing wave within the cavity. These wavelengths are determined by the distance between the mirrors and the refractive index of the medium between them.

The principle of operation relies on multiple beam interference. When light enters the cavity, a portion is transmitted through the first mirror. The light then reflects off the second mirror and travels back towards the first. A portion of this reflected light is transmitted through the first mirror, and this transmitted light is in phase with the initial transmitted light if the round trip path length is an integer multiple of the wavelength. This constructive interference leads to a strong transmission at resonant wavelengths. Conversely, at wavelengths that do not satisfy this condition, destructive interference occurs, resulting in low transmission.

Fabry-Pérot cavities have numerous applications in optics and physics. They are fundamental components in lasers, where they provide the necessary feedback mechanism for sustained oscillation. They are also used in spectroscopy for high-resolution measurements of spectral lines, in optical filters to select specific wavelengths of light, and in optical sensors for detecting small changes in environmental conditions. The finesse of a Fabry-Pérot cavity, which quantifies the sharpness of its transmission peaks, is a crucial parameter related to the reflectivity of the mirrors and the losses within the cavity.