HIGH-POWER INTERFEROMETRIC PHASE MEASUREMENT LIMITED BY QUANTUM-NOISEAND APPLICATION TO DETECTION OF GRAVITATIONAL-WAVES

Interferometric detection of gravitational waves at levels of astrophy sical interest is expected to require measurement of optical phase dif ferences of less than or equal to 10(-10) rad. To achieve this sensiti vity the measurement must be made at the quantum (shot noise) limit. W e have built a laboratory-scale interferometer to investigate limits t o sensing the phase at this level, and obtained, with 70 W of circulat ing power, a phase sensitivity limited by shot noise of 3 X 10(-10) ra d/root Hz at frequencies above 1.5 kHz. We describe the experiment and discuss the implications for the Laser Interferometer Gravitational-W ave Observatory (LIGO).