optical cavity

An optical cavity or optical resonator is an arrangement of mirrors that forms a standing wave cavity resonator for light waves. Optical cavities are a major component of lasers, surrounding the gain medium and providing feedback of the laser light. They are also used in optical parametric oscillators and some interferometers.
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A region bounded by two or more mirrors that are aligned to provide multiple reflections of lightwaves. Note: The resonator in a laser is an optical cavity. In this sense, synonym resonant cavity.