Abstract

We have experimentally and theoretically investigated the coherence properties and phase dynamics of spatially coupled Nd:YAG lasers as a function of overlap of their fields. The dependence of phase locking on the overlap and detuning of the lasers, as well as noise sources, are studied. The coherence of the laser sources is directly determined from the visibility of interference fringes as recorded by a video camera system. Heterodyne measurements are used to determine the detuning between individual lasers. It is found that the lasers remain phase locked even when the overlap of their fields is extremely small, but then they display an abrupt transition to incoherence. When phase locked the laser fields are 180° out of phase with each other. A phase mask fabricated by binary optics procedures may be used to alter the phase relationship between the laser sources. Numerical solutions of a laser model that show very good agreement with experimental measurements will be presented, and the coherence-incoherence transition will be interpreted theoretically.

© 1992 Optical Society of America