Adaptive aberration correction using feedback interferometry

Abstract

There has recently been much interest in the use of adaptive optics systems for automatic aberration correction in applications such as astronomical imaging. This thesis describes a novel approach to this problem which uses an unusual interferometer operating together with a liquid crystal spatial optical phase modulator. The interferometer is a feedback interferometer, in which the two-dimensional output fringe intensity distribution maps the phase aberrations of the input beam, and is fed back to the phase modulator which is located in one of the interferometer arms. The feedback system enables the interferometer to track variations in the two dimensional phase distribution of the input beam, and automatic aberration correction then becomes possible. The thesis describes the principles of operation of this type of feedback interferometer, the construction and calibration of the special-purpose liquid crystal phase modulator used in the work, and construction and testing of the feedback interferometer itself. The thesis also presents theoretical results obtained by computer simulation which show that aberration correction is possible, and experimental results which confirm this.