The Effect of Aberrations and Apodisation on the Performance of Coherent Imaging Systems.

Abstract

Abstract : The effect of aberrations on coherent imaging systems and the utility of apodisation in improving the performance of such systems was theoretically and experimentally investigated. The imaging performance of these systems was evaluated in terms of the images of certain simple objects--a point, two closely-spaced points, an edge, and a slit. Apodisation is defined as the deliberate modification of the amplitude transmittance of the exit pupil of the optical system. The effects on the imaging performance for various amounts of defocus, astigmatism, coma, and spherical aberration were determined for both unapodised and apodised systems. It is well known that for an aberration-free system, apodisation is effective in moderating the deleterious effects of the coherent imaging process. Since all real optical systems have aberrations, this dissertation addressed the more general case of apodisation in aberrated coherent imaging systems. It was found that apodisation was effective in improving the performance of these aberrated systems, i.e., ringing in the image of an edge or slit was greatly reduced and the mensuration error in the image of two points was almost eliminated. The performance of an unaberrated system was seen to be a special case. Experiments have been conducted which verified the theoretical model which was used to make extensive theoretical predictions. Keywords include: Apodisation, Coherent imaging, Imaging, and Aberrations.