The Non-Mechanical Beam Steering of Light in Reflective Inverse Diffusion
AIR FORCE INSTITUTE OF TECHNOLOGY WRIGHT-PATTERSON AFB OH WRIGHT-PATTERSON AFB United States
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Wavefront shaping is a technique that uses spatial light modulators to conjugate the phase of light incident on a rough surface, such that the light will refocus after reflection. This refocusing effect is called reflective inverse diffusion. There currently are two different approaches used to achieve reflective inverse diffusion iterative methods and matrix methods. Iterative methods find one phase mask which allows for reflected light to be focused at a single, specific position, with results that are immediately available and continuously improving. Matrix methods calculate the complex matrix which describes the rough surface and allows for reflected light to be focused at many positions after reflection and at multiple spots simultaneously. However, matrix methods are susceptible to decreased performance in a noisy system, and their results are not immediately available. This thesis provides an alternative to the current paradigm of choosing between iterative methods and matrix methods by showing that beam steering can be integrated into existing iterative methods, giving them the multiple-spot capabilities of matrix methods. For a focal plane system, a genetic algorithm not previously used for reflective inverse diffusion is used to find a phase mask that focuses light to one point. Circular shifts are then applied to the phase mask that create phase tilts at the rough surface and steer the reflected spot at the cost of decreased enhancement with a larger shift.