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Proceedings Paper

Calibration methods for a dual-wavelength interferometer system
Author(s): Yanqi Zhang; Martin Tangari Larrategui; Thomas G. Brown; Jonathan D. Ellis
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Paper Abstract

Multiple wavelength interferometry has long been considered an option for the measurement of large aspheric slope departures. In particular, a synthetic wavelength offers a variety of approaches by which large phase excursions can be unwrapped. Using multiple wavelengths can create collimation and magnification mismatch errors between the individual wavelengths that arise during beam expansion and propagation. Here, we present and analyze alignment and calibration methods for a dual-wavelength interferometer that can significantly reduce both misalignment errors and chromatic aberrations in the system. To correct for misalignment, a general method is described for the alignment of a dual-wavelength interferometer, including the alignment of lasers, beam expanders, beam splitters for combining beams and for compensating errors in the reference surface, and the fringe imaging system. A Fourier transform test at the detector surface was conducted to validate that there is essentially no magnification difference between two wavelengths resulting from misalignment of optical system. For the chromatic aberration introduced by the optical elements in the system, a ray-trace model of the interferometer has been established, to simulate the chromatic effect that optical elements will have on the measurement results. As an experimental test, we examine an off-axis spherical mirror in a non-null condition using a highly aliased interferogram. The above alignment methods and the results are analyzed based on the simulated system errors. Using this method, we demonstrate a measured surface profile of deviation of λ/25 which is comparable to a direct measurement profile of the surface on axis using a Fizeau interferometer.

Paper Details

Date Published: 19 September 2018
PDF: 13 pages
Proc. SPIE 10747, Optical System Alignment, Tolerancing, and Verification XII, 1074707 (19 September 2018); doi: 10.1117/12.2323127
Show Author Affiliations
Yanqi Zhang, The Institute of Optics, Univ. of Rochester (United States)
Martin Tangari Larrategui, The Institute of Optics, Univ. of Rochester (United States)
Thomas G. Brown, The Institute of Optics, Univ. of Rochester (United States)
Jonathan D. Ellis, College of Optical Sciences, The Univ. of Arizona (United States)

Published in SPIE Proceedings Vol. 10747:
Optical System Alignment, Tolerancing, and Verification XII
José Sasián; Richard N. Youngworth, Editor(s)

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