Virtual interferometer calibration method of a non-null interferometer for freeform surface measurements

Qun Hao, Shaopu Wang, Yao Hu*, Hanglin Cheng, Meng Chen, Tengfei Li

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

53 Citations (Scopus)

Abstract

Non-null interferometry is a prospective method for aspheric and freeform surface measurements because of its potential versatility over null interferometry. Due to the existence of the retrace error, non-null testing usually has the drawbacks of low accuracy and inconvenient alignment of the surface under test (SUT). In this paper, a calibration method for freeform SUT in a non-null interferometer is introduced. This method calibrates the position and attitude of the SUT in a virtual interferometer with an optimization algorithm, and no accurate adjustment mechanism is required to adjust the SUT in the real interferometer. An application of this method in the digital moiré interferometric technique (DMIT) is presented. The retrace error and the influence of the alignment error can be removed after calibration. Experimental results indicate that with this calibration method, the DMIT can achieve a measurement repeatability of λ/20 (PV) when the freeform SUT has obvious alignment error. This is adequate for most aspheric and freeform surface measurements, especially when the vibration cannot be isolated completely and the freeform SUT is not easy to align.

Original languageEnglish
Pages (from-to)9992-10001
Number of pages10
JournalApplied Optics
Volume55
Issue number35
DOIs
Publication statusPublished - 10 Dec 2016

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