Hologram fringe stabilization method

A technique is developed for stabilization and precision control of the phase of fringes at the hologram plane. The technique is employed in a system requiring phase control and resettability to within 10 deg. Two waves exposing the hologram are mixed by an auxiliary grating previously recorded by those two waves. Lock-on operations and the feedback system are described, and the method is compared to other fringe stabilization approaches. Optimum placement of the control grating, advantages of using a nonabsorbing medium for the grating, precision adjustments of the control grating, and the advantage of the technique when working with very fine fringes and low light levels are discussed.