HOLOGRAPHIC OPTICAL-ELEMENTS IN THE PRESENCE OF SPHERICAL-ABERRATION AND FOCUS ERROR - SOME REMARKS ON IMAGING QUALITY

When aberrations are small, it is possible to use wave aberration vari ance to obtain the position of the best image plane in both convention al and holographic optical systems. However, when aberrations increase , this measurement is not sufficient and it does not provide the corre ct plane position for the best image. In this paper, two alternative m ethods for evaluating image quality in spherically aberrated on-axis h olographic lenses are compared. These two methods are the standard dev iation of the distribution of light intensity and entropy. Both method s are based on the calculation of the diffraction integral and the sub sequent analysis of the distribution of light intensity as a probabili ty density function for each image plane being analysed. Even though t he results obtained with both methods are identical when aberrations a re small, only entropy provides the best image when the value of these aberrations increases.