Correction for mapping errors in non-null test of aspheric surface

W Weibo,Z Mengqian,F Zhigang,Y Siwen,L Jian

doi:10.2971/jeos.2015.15032

Abstract

The non-null testing methods have the potential to allow measurement of aspheric surfaces with large departures from a reference sphere. In a non-null configuration, the ray will return along a different path and interfere with a different reference ray. This difference in “mapping” between the test and reference rays creates an additional optical path difference (OPD) contribution, which causes test part errors to be mapped to the wrong location. To correct the mapping errors in non-null test of aspheric surface, correction method are proposed by ray trace and wave-front analysis. Experiments are carried out to illustrate the effectiveness of this approach. The methods can work well, despite large deviation between the theoretic value of the aspheric and the reference wave-front.

Highlights

INTRODUCTIONThe rays from the test part follow exactly the same path through the optical system as the reference rays and no systematic errors are induced
Traditional interferometry is done in a null or near-null condition
The rays from the test part follow exactly the same path through the optical system as the reference rays and no systematic errors are induced. This null condition indicates the shape of the measured object is nearly identical to that of the reference and small deviations from the null are linearly proportional to the differences between them

Summary

INTRODUCTION

The rays from the test part follow exactly the same path through the optical system as the reference rays and no systematic errors are induced This null condition indicates the shape of the measured object is nearly identical to that of the reference and small deviations from the null are linearly proportional to the differences between them. For the sub-aperture stitching test of aspheric surface, the mapping is crucial for stitching into a unified map, when placing the sub-aperture data onto a global coordinate plane If this effect is not corrected, the ill-conditioned character of the stitching process means that, even though the distortion may appear to be a minor factor within each sub-aperture, significant errors can be introduced to the stitched data. Received May 28, 2015; revised ms. received June 11, 2015; published June 26, 2015

MAPPING ERROR ANALYSIS OF NON-NULL ASPHERIC TESTING

Measurements of spherical surfaces in non-null condition

Measurements of aspheric surfaces in non-null condition

CONCLUSION