Adaptive wavefront correction using a VLSI implementation of the parallel gradient descent algorithm

An adaptive laser beam focusing system using a 127 channel liquid crystal phase modulator is presented. The controller for the system is a circuit built with prototype VLSI chips that implement the stochastic parallel gradient descent algorithm. The controller is driven by a scalar laser beam quality metric and can run at the rate of 150 kHz. The system performance is characterized and a secondary control loop manipulating one of the algorithm parameters is experimentally investigated. The performance of the system is reported and performance improvements obtained by using the recent history of the beam quality metric to control an algorithm parameter is demonstrated.