Calibration methods for a dual-wavelength interferometer system

Yanqi Zhang; Martin Tangari Larrategui; Thomas G. Brown; Jonathan D. Ellis

doi:10.1117/12.2323127

19 September 2018 Calibration methods for a dual-wavelength interferometer system

Yanqi Zhang, Martin Tangari Larrategui, Thomas G. Brown, Jonathan D. Ellis

Proceedings Volume 10747, Optical System Alignment, Tolerancing, and Verification XII; 1074707 (2018) https://doi.org/10.1117/12.2323127
Event: SPIE Optical Engineering + Applications, 2018, San Diego, California, United States

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.

Citation Download Citation

Yanqi Zhang, Martin Tangari Larrategui, Thomas G. Brown, and Jonathan D. Ellis "Calibration methods for a dual-wavelength interferometer system", Proc. SPIE 10747, Optical System Alignment, Tolerancing, and Verification XII, 1074707 (19 September 2018); https://doi.org/10.1117/12.2323127

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KEYWORDS

Wavefronts

Interferometers

Calibration

Imaging systems

Interferometry

Beam splitters

Chromatic aberrations

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