We are developing an instrument, the Geometry Measuring Machine (GEMM), to measure the profile errors of aspheric and free form optical surfaces, which require measurement uncertainties near 1nm. Using GEMM, an optical profile is reconstructed from a set of measured curvature values. We will describe a prototype version of GEMM, its calibration practice, and the measurement site registry practice needed to make nanometer resolution comparisons with other instruments. As a demonstration of GEMM, profiles of an elliptical mirror were measured with GEMM and the NIST Moore M-48 Coordinate Measuring Machine. Using a version of Student''s t Test the profiles were compared and found indistinguishable at the 99% confidence level; and to have a 22 nm peak-to-valley or 6rms deviation. Finally the repeatability of GEMM was evaluated and found to be < 12 nm peak-to-valley.
Citation: Journal of Research National Institute of Standards and Technology
Volume: 111 (5)
Pub Type: Journals
precision optics, precision surface, profilometry