Introduction and overview

In the year 1851 Foucault demonstrated that the slow rotation of the plane of vibration of a pendulum could be used as evidence of the earth's own rotation. The first optical experiment to detect the earth's rotation was performed by Michelson and Gale (Michelson, 1925a, b) using an unusually large size for an interferometer: 0.4 miles × 0.2 miles. Nowadays high precision measurements of the earth's rotation are performed by using radio telescopes in very long baseline interferometry (Johnson et al., 1979). Moreover, a recent proposal (Small and Chow, 1982) take advantage of the ultra high sensitivity of a ring-laser gyroscope (Aronowitz, 1965, 1971; Chow et al., 1985; Menegozzi and Lamb, 1973; Privalov and Fridrikhov, 1969) of 10 m diameter to monitor changes in earth rate or universal time. The underlying principle of such a device is the optical analog of the Foucault pendulum, the so-called Sagnac effect (Post, 1967; Sagnac, 1913a, b). The frequencies of two counterpropagating waves in a ring interferometer are slightly different when the interferometer is rotated about an axis perpendicular to its plane. Since this frequency difference is proportional to the rotation rate it provides a direct measure of the rotation of the system.

Ring-laser gyroscopes of this size would also allow tests (Schleich and Scully, 1984; Scully, Zubairy and Haugan, 1981) of metric gravitation theories (Misner, Thorne and Wheeler, 1973).