Ring laser gyroscope
Instrument to measure angular velocity / From Wikipedia, the free encyclopedia
For a somewhat similar system that uses fibre optic cables, see fibre optic gyroscope.
A ring laser gyroscope (RLG) consists of a ring laser having two independent counter-propagating resonant modes over the same path; the difference in phase is used to detect rotation. It operates on the principle of the Sagnac effect which shifts the nulls of the internal standing wave pattern in response to angular rotation. Interference between the counter-propagating beams, observed externally, results in motion of the standing wave pattern, and thus indicates rotation.