Sub-aperture stitching computation time optimization using linear equations system

Abstract

Measurement of large or aspheric optical surfaces shape as single aperture using interferometry is problematic due multiple reasons. Typical problem is numerical aperture limitation of the interferometer transmission element. Aspheric surfaces are also problematic due a significant shape deviation from the illumination wavefront. This deviation typically causes vignetting and spatial aliasing on the camera. A solution is sub-aperture measurement and subsequent subaperture stitching. A stitching algorithm in principle uses overlaps between sub-apertures to eliminate aberrations of each sub-aperture to obtain a full-aperture for further analysis. This process is computation time demanding and an optimization has to be implemented in order to obtain result in reasonable time. In this paper, descriptions of considered aberrations using Zernike polynomials are presented and the stitching method based on linear equation system is proposed and it is mathematically described. The method was practically tested with real data measured on spherical surfaces using QED ASI and the results are presented. Stitching quality was quantified for results and compared to other stitching methods.