RADIATION PRESSURE AND STABILITY OF INTERFEROMETRIC GRAVITATIONAL-WAVE DETECTORS

The effect of radiation pressure on the stability of Fabry-Perot cavit ies with hanging mirrors is investigated. Such cavities will form an i ntegral part of the laser interferometric gravitational-wave detectors that are being constructed around the globe. The mirrors are hung by means of a pendulum suspension and are locked by servo controls. We as sume a realistic servo-control transfer function that satisfies the st andard stability criteria. We find that for positive offsets from the resonance of the cavity the system is stable. However, we show that fo r negative offsets instabilities can occur, although the servo system has the effect of increasing the instability threshold, compared with the nonservoed case. Conditions for stability are finally given, invol ving the finesse of the cavity, the input power, the mass of the mirro rs, the servo gain, and the phase detuning from perfect resonance. Gra vitational-wave detectors with arm cavities having a finesse as low as approximately 200 could exhibit instabilities. Some implications for the locking of these detectors are finally given. (C) 1998 Optical Soc iety of America.