Reflective optical cavity

A laser consists of a highly reflective optical cavity, which contains mirrors and a gain medium. The gain... 

The word laser is an acronym for light amplification by the stimulated emission of radiation. Lasers of all kinds consist of several basic components an active medium, an outside energy source, and an optical cavity with carefully designed mirrors on both ends. One of the mirrors is 100 percent reflective... 

As the emitted radiation bounces back and forth between the two mirrors, it becomes coherent. Some of the energy traveling back and forth through the optical cavity is transmitted though the less reflective mirror and becomes a laser beam. 

Enhancement of the Hght-matter interaction in a microscopic optical cavity is achieved because Hght trapped in the cavity has longer effective interaction time with absorbers. For short laser pulses, cavity length exceeding CTp allows avoidance of the interference between the pulses incident and reflected from the mirrors. Spectral selectivity of planar Fabry-Perot cavities can be used to achieve the localization at the resonant wavelength of the cavity. 

The photon thus induced to be emitted has the same phase relationship as the inducing photon. Further amplification of this coherent emission is brought about in a resonant optical cavity containing two highly reflecting mirrors, one of which allows the amplified beam to come out, either through a pin-hole or by a little transmission (Section 10.4). 

Principal components of a laser (1) Gain medium (gas, liquid, or solid crystal, e.g,. ruby) inside the optical cavity, (2) input pumping energy (e.g., from flash lamp), (3) high-efficiency reflector ( 100% reflectivity), (4) low-efficiency mirror, that is, output coupler ( 95% reflectivity), (5) output laser beam. Components (3) and (4) form the optical cavity, also known as a Fabry-Perot interferometer. 

In 1960, Theodore Maiman of the Hughes Research Laboratories produced the first laser using a ruby crystal as the amplifier and a flash lamp as the energy source. The helical flash lamp surrounded a rod-shaped ruby crystal, and the optical cavity was formed by coating the flattened ends of the ruby rod with a highly reflecting material. In operation, an intense red beam emerged from the ends of the rod when the flash lamp was initiated. 

CRDS is based on measuring the intensity decay rate of ahghtpulse trapped in an optical cavity, formed by two high-reflectivity mirrors (R > 0.999). The principle of the method can be explained with refer-... 

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