Coherent optical adaptive techniques: design and performance of an 18-element visible multidither COAT system.

Coherent Optical Adaptive Techniques (COAT) offer promise for overcoming the deleterious effects of phase distortions experienced by optical beams propagating in a turbulent and absorbing atmosphere. An 18-element, visible wavelength, multidither COAT system is described. The all solid-state servosystem design was based on the results of an extensive computer simulation. The optical system uses a 0.488-microm argon laser and an array of beam splitters, phase shifters, and beam combiners (termed a phasor matrix) to form the output array. To date, 6- and 8-element linear arrays and an 18-element axisymmetric array have been investigated. The system has demonstrated a convergence time of 1.2 msec and can form the array with a strehl ratio of 0.67. Moving glint tracking, multiple glint discrimination, and offset pointing from a fixed reference have been demonstrated. Good agreement has been observed between measured system results and theoretical predictions.