Interferometric Lens Testing

Abstract

Abstract : Interferometric testing of optical systems measures the pupil function, or wavefront deviations from a reference sphere, of the lenses and mirrors. From this pupil function, the optical transfer function (OTF), spread function, and aberration coefficients may be computed. In the present study, a wavefront shearing interferometer (WSI) is developed and applied to the on-axis testing of lenses. The simple cube interferometer has all the interferometric adjustments built in during assembly. In contrast to most interferometric test systems, the WSI is inexpensive, portable, relatively insensitive to vibration, does not need laser illumination, and requires only a minimum of experimental time and operational expertise. Scanning the interferograms and subsequent data reduction are the major effort in testing with the WSI. A computer program for reducing input fringe data to the pupil function, OTF, and aberration coefficients is described; a program to plot the pupil function and OTF is included. Also, a computer program for deriving fringe locations from density data obtained with automatic scanning of the interferograms is described. Sample outputs of the computer programs are given.