page 1 of 15 HIGH POWER INTERFEROMETRIC PHASE MEA- SUREMENT LIMITED BY QUANTUM NOISE AND APPLICATION TO DETECTION OF GRAVITA- TIONAL WAVES P. FRITSCHEL, G. GONZÁLEZ * , B. LANTZ, P. SAHA † AND M. ZUCKER DEPARTMENT OF PHYSICS AND CENTER FOR SPACE RESEARCH, MASSACHUSETTS INSTITUTE OF TECHNOLOGY ,CAMBRIDGE, MA 02139 ABSTRACT Interferometric detection of gravitational waves at levels of astrophysical interest is expected to require measurement of the optical phase difference of ≤10 -10 radians. To achieve this sensitivity the measurement must be made at the quantum (shot noise) limit. We have built a laboratory-scale interferometer to investigate limits to sensing the phase at this level, and obtained, with 70 W of circulating power, a phase sensitivity limited by shot noise of at frequencies above 1.5 kHz. We describe the experiment and discuss the implications for the Laser Interferom- eter Gravitational-wave Observatory (LIGO). PACS numbers: 04.80.Nn, 0760.Ly, 42.50.Ar, 95.55.Ym *Current address: Pennsylvania State University, Department of Physics, 104 Davey Laboratory, University Park, PA 16802. †Current address: Imatron Inc., 389 Oyster Pt. Blvd., S. San Francisco, CA 94080-1998. 3 10 – ×10 rad/ Hz