Two-dimensional stitching interferometry based on tilt measurement.

In this paper, a two-dimensional stitching interferometry system using two tiltmeters is proposed. During the scanning and the measurement, one tiltmeter stays with the interferometer and the other one is attached to the translation stage where the surface under test is placed. The differences of the x- and y-tilt readings between these two tiltmeters are recorded as the relative tilt between interferometer and surface under test. The relative tilt in both x- and y-directions are used to correct the surface tip/tilt of each subset, and then the piston is adjusted to get the final stitching surface map. As an example, a stitching result of a 125mm-long mirror surface is presented. The repeatability of our current stitching system is about 1.48 nm RMS. The stitching result is compared to the result of a one-dimensional angular-measurement-based stitching method to discuss the merits and limitation of the proposed method.