Dynamic illumination in Phase-shifting Interferometry

Abstract
Phase-shifting interferometry1 is the premier measurement technique for high-precision surface form metrology. Generally, the measurement cavity is illuminated with a stationary, on-axis, point-like source of coherent light situated at the interferometer source plane. We describe how to enable a variety of useful functions to aid interferometric metrology applications by dynamically moving the source point during a phase-shifting measurement using steering mirror technology. Called Dynamic Illumination, these motions describe trajectories that often take the form of geometric primitives like points, lines, arcs, circles, and spirals. A fixed point on the optical axis represents conventional operation, but measurements using different trajectories enable different functions. We highlight three exemplary functions in this paper; phase shifting, autofocus, and coherent noise reduction techniques.

Keywords: PSI, interferometry, optical metrology, surface measurement, non-contact metrology