A large scale passive laser gyroscope for Earth rotation sensing.

Rotation sensing of Earth has many applications in different disciplines, such as monitoring of ground motions, the establishment of UT, and the test of the relativistic Lense-Thirring effect. We report the development of a large scale passive resonant gyroscope (PRG) with a meter size optical ring cavity. By locking a pair of laser beams to adjacent modes of the square ring cavity in the clockwise and counter-clockwise directions, we achieve a rotation resolution of 7E-10 rad/s at an integration time of 4000 s. The PRG detects the tiny rotation motions of the housing platform, and the rotation sensitivity reaches a level of 2E-9 rad/s/rtHz in the 5-100 Hz region, currently limited by the detection noise, residual amplitude modulation and the instability of the cavity length. Our result improves the rotation sensitivity of the PRGs to a new level, and indicates that PRGs have a great potential to be a high resolution Earth rotation sensor at much smaller cost.