Editing Ring laser gyroscope (section)

{{Short description|Instrument to measure angular velocity}}
{{for|a somewhat similar system that uses fibre optic cables|fibre optic gyroscope}}
[[File:Ring laser gyroscope at MAKS-2011 airshow.jpg|thumb|Ring laser 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 (wave propagation)|Interference]] between the counter-propagating beams, observed externally, results in motion of the standing wave pattern, and thus indicates rotation.