Lock-in holography using optically addressed multiple-quantum-well spatiallight modulators

Perpendicular-field multiple-quantum-well optically addressed spatial light modulators have a response that saturates at high writing intensity. This limits the diffraction efficiency of low-fringe-visibility holograms. This effect is suppressed by use of the ability of these structures to subtract images rapidly. The modulator is exposed to a hologram with a spatially uni form beam, which is incoherent with the hologram, superimposed on top of it . Pulsing the hologram synchronously with the device drive voltage but leav ing the uniform beam constant in time can build up the diffraction to large values even when the fringe visibility is low.