Proposed optical test of metric gravitation theories

An optical test of the metric theories of gravitation which employs a ring laser interferometer in an earthbound laboratory is suggested and analyzed. The proposed test would be sensitive to the presence of a preferred frame of the universe and to the geodetic and Lense-Thirring (frame-dragging) rotations of the local inertial frames relative to fixed stars. The frequency difference of the counterpropagating beams in a Sagnac-type experiment is determined within the framework of the parametrized post-Newtonian formalism. The precision with which the various parameters involved in the expression for the frequency difference can be measured is discussed.