Self-referenced Surface Profilometry

INTRODUCTION In optical surface metrology the reference surface is usually self-calibrated against the part under test because the errors in the reference are of the same order as those in the part under test. The self-calibration, or “absolute test”, is typically done by making three interferometric measurements, an initial measurement and then two more with the part under test shifted laterally slightly in orthogonal directions to obtain data sheared between reference and test part. This procedure allows one to recover the topography of both the reference and the test part.