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Fizeau Interferometry with Tunable-Wavelength Lasers

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Peter de GROOT

Zygo Corporation, Middlefield, CT United States

In the 1990’s, it was still common for laser Fizeau interferometers of large size--capable of measuring parts more than 50 cm in diameter—to rely on a visual or automated analysis of static fringe patterns. Phase shifting interferometry, which traditionally require mechanical motions of the reference optic or the part itself, is impractical for such large systems. The solution is to sweep the wavelength of an external-cavity laser diode source to generate phase shifts without mechanical motions in the interferometer.

Further advances in wavelength-tuned interferometry have launched a series of revolutionary innovations in optical testing. Today, Fourier transform methods with dynamic wavelength tracking allow for simultaneous measurement of the front and back surfaces as well as the material homogeneity of plane-parallel parts. Applications include quality testing of glass substrates for computer rigid disk drives, planar waveguides for augmented reality systems, cover glass for portable displays, and high-precision optical flats. Model-based data analysis significantly enhances environmental robustness, and absolute distance measurements of part position optimize instrument focus automatically.

In this presentation, I review the principles, history, applications, and current state of the art for tunable-wavelength interferometry, including on-going research and perspectives on future developments.

Peter de Groot, PhD, is the Executive Director of R&D at ZYGO Middlefield, and is the head of the Innovations Group, which focuses on the invention and concept demonstration of new optical metrology instruments. He is a Fellow of the SPIE, the Optical Society of America, the Institute of Physics, and the International Academy of Engineering Technology. A multiple award winner for innovation, Peter is also a conference organizer, a scientific committee member, tutorial instructor, honorary professor, and an active contributor in the optics community.