Readout and control of a power-recycled interferometric gravitational-waveantenna

Interferometric gravitational-wave antennas are based on Michelson interfer ometers whose sensitivity to small differential length changes has been enh anced by the addition of multiple coupled optical resonators. The use of op tical cavities is essential for reaching the required sensitivity but sets challenges for the control system, which must maintain the cavities near re sonance. The goal for the strain sensitivity of the Laser Interferometer Gr avitational-Wave Observatory (LIGO) is 10(-21) rms, integrated over a 100-H z bandwidth centered at 150 Hz. We present the major design features of the LIGO length and frequency sensing and control system, which will hold the differential length to within 5 x 10(-14) m of the operating point. We also highlight the restrictions imposed by couplings of noise into the gravitat ional-wave readout signal and the required immunity against them. (C) 2001 Optical Society of America.