SAGNAC INTERFEROMETER FOR GRAVITATIONAL-WAVE DETECTION

We have investigated a zero-area Sagnac interferometer as abroad band gravitational-wave detector. Frequency response measurements of a labo ratory-scale interferometer are in excellent agreement with theory. Th e measured contrast ratio, 0.996, is insensitive to induced birefringe nce, laser-frequency variation, arm imbalance, and dc mirror displacem ent. A near shot-noise-limited phase sensitivity of 3 x 10(-9) rad/roo t Hz was measured at the interferometer's maximum sensitivity frequenc y, 90.9 MHz.