Lock-in holography using optically-addressed multiple quantum well spatial light modulators

Summary form only given. Perpendicular field multiple quantum well optically addressed spatial light modulators (MQW OASLMs) have been shown to exhibit high speed, resolution and sensitivity to light. They have been applied to optical correlation and non-destructive evaluation (NDE) of materials. One drawback of these devices is that their response saturates at high writing intensities. This saturation intensity is a function of the device´s material parameters and the cycle time of the ac voltage that is applied to them. It is possible to overcome this problem by using the ability of perpendicular field MQW OASLMs to perform rapid image subtraction. Under the proper conditions, the image retained in an MQW OASLM after one complete voltage cycle is the difference of the image on the writing beams on the positive and negative cycles of the voltage. By synchronizing the coherent writing beams with the applied voltage so that they are on only during the positive (or negative) part of the cycle it is possible, over many cycles, to build up a strong hologram even when an incoherent (but not temporally modulated) background field much stronger than the writing beam is present. We performed this experiment using a reflective mode PIN GaAs/AlGaAs MQW OASLM.