Experimental Validation of the Extended-Nijboer-Zernike (ENZ) based Aberration Retrieval Method for Microscope Objectives

The quality of optical systems is conventionally assessed by interferometric tools requiring special setups and environmental conditions. The aberration retrieval method presented here relies only on intensity measurements in the focal region of the imaging system being tested. A simple setup for the measurement of through-focus intensity distributions of a microscope objective is presented. The wavefront in the exit pupil of a microscope objective (NA=0.4) is reconstructed from the intensity distributions of up to 30 focal planes. Two measurements have been performed. One of the single microscope objective and a second measurement with an additional aberration plate inserted close to the entrance pupil of the objective. The first measurement is used for calibration of the setup while the difference between both measurements depends only on the aberration plate and is independent of all constant systematic aberrations of the setup. Comparisons of the ENZ measurements with interferometric measurements showing an agreement better than Lambda/70 (rms) are presented.