Phase measurements in the focal region of an aberrated lens

Thesis (Ph. D.)--University of Rochester. College of Engineering and Applied Science. Institute of Optics, 1981. This thesis was digitized by the Institute of Optics in 2014 and was determined to have lapsed into the public domain. If you are the author and have questions about the digitization of your work, please contact Kari Brick, Graduate Program Coordinator for the Institute of Optics, at kbrick@ur.rochester.edu. Other contact information for the Institute is available at http://www.optics.rochester.eduThe intensity and phase distributions in the focal region of an aberrated lens have been studied both theoretically and experimentally. For computing the intensity and phase distributions, three methods - the Nijboer-Zernike method, the asymptotic method and the discrete Fourier transform - have been compared. The discrete Fourier transform has been found to be the most useful method for treating a wide range of aberrated lenses. The intensity and phase distributions have been computed for a variety of theoretical lenses. It has been observed that in some cases the phase distribution is a much more sensitive indicator of the presence of aberrations than the intensity distribution. It has also been found out that phase measurements provide a very accurate method for locating the zero points of the intensity due to the multivaluedness exhibited by phase around these points. An interferometer has been constructed as a combination of a Mach-Zehnder and a Twyman-Green interferometer for characterizing a lens both in the focal region and in the pupil. Both measurements can be performed without disturbing the orientation of the lens with respect to the plane wave illuminating it. Consequently, the focal region results and the pupil function of the lens may be correlated without any ambiguity regarding the orientation of the lens. For rapid and precise measuring of the phase, both interferometers function as AC-interferometers. The experimental apparatus is driven and the data are acquired and processed by a microcomputer. The intensity and phase distributions of a number of real lenses have been measured in their focal regions. Visual comparisons have been made and qualitative correlations have been established between the aberration coefficients and focal properties of the lenses. Determining the aberration coefficients of a lens from focal region phase measurements is severely complicated by the presence of phase discontinuities, which are due to the above mentioned multivaluedness of the phase. These prevent the extraction of the aberration coefficients by fitting computed models to measured data. Nevertheless, a substantially greater amount of information regarding the performance of high quality imaging optics is obtained through focal phase measurements than by the means of the classical star test, i.e., intensity measurements