Sub-pixel spatial resolution interferometry with interlaced stitching

Abstract

In this paper we describe a growing need for an increase in the spatial resolution of interferometric surface measurements of precision optics and present a new method to address this need. An increase in the spatial resolution of interferometric surface measurements arises from evolving surface figure and micro-roughness specifications for higher quality optics, demand for larger optics, and recent advancements in deterministic polishing. These three topics will be discussed and their relationship to increased spatial resolution will be described. A solution to increase the spatial resolution using a process called spatial resolution interferometry will be presented. In this process, multiple interferometric measurements are made as the optic under test (or the CCD array) is shifted at sub-pixel increments. The measurements are then combined to construct a measurement with higher spatial resolution than the original measurements. Initial results obtained using this process with a commercially available Fizeau interferometer will be presented.