High sensitivity rotation measurements with a mid-size laser gyroscope

An high sensitivity laser gyroscope is presented operating in a square cavity of side length of the order of 1 m with a measured sensitivity limit at the level of 2 10-9(rad/s)/ √Hz. We report on the active stabilization of the laser optical frequency which is mainly driven by the environmental thermal fluctuations and the experimental results obtained with the active stabilization system are given. Finally the applications of this gyrolaser as an high-sensitive tilt-meter in Virgo, the large-frame interferometer for gravitational waves detection, are discussed