Laser gyro mode locking reduction scheme

Abstract

A ring laser gyroscope is described having two counterpropagating primary modes and one or more secondary laser modes having a component c cos .omega. t to produce a dithering effect which reduces or eliminates the lock-in range of the primary modes. The ratio of c to .omega. is controlled to minimize J.sub.o (c/.omega.) wherein J.sub.o is the Bessel Function of the first kind of zero order. In one embodiment, cavity length control circuitry is adjusted to detune the cavity length to allow two secondary opposing modes of angular frequency separation .omega. to be generated within laser gain medium in the cavity while two primary counterpropagating modes operate well above threshold. Another embodiment has an external laser beam source for generating two secondary waves, at two light frequencies separated by an angular frequency .omega., which are introduced into the ring laser path through a partially transmitting mirror which forms one of the corners of the ring laser closed loop path. In still another embodiment, part of one of the primary waves leaves the ring laser path through a partially reflective mirror and is acted upon by a mirror oscillating at an angular frequency .omega. which doppler-shifts the frequency of the extracted wave. This doppler-shifted mode is reintroduced into the ring laser path to diminish the range of lock-in frequency of the primary modes. In all embodiments, the magnitude of the ratio of c/.omega. is controlled to minimize J.sub.o (c/.omega.) to reduce the range of lock-in of the primary modes.