Multiple Subaperture Interferometric Testing of Full Spheres

Abstract

The objectives of this work are to develop nondestructive, optical test techniques to estimate optical path difference (OPD) errors of full spheres (e.g., gyroscopes, ball hearings, micro-balloons). We propose to use a multiple subaperture interferometric test modeled after analogous techniques used in full aperture testing of large optical systems1. A spherical harmonic base set of polynomials for full sphere descriptions is developed, together with the numerical methods for fitting these polynomials to obtain the aberration coefficients over the spherical surface. The physical interpretation of the lower order terms with respect to OPD errors for a spherical body are discussed and demonstrated using three-dimensional graphics representations. A computer simulation of the multiple subaperture technique for full spheres is utilized in an analysis of test accuracy as a function of various test design parameters (subaperture size, number of subapertures, subaperture tilt errors, inter-subaperture phasing errors, etc.). The results of the simulation suggest that optical testing of full spheres is feasable and has the potential for increased speed, accuracy, and surface preservation as compared to direct physical methods.