Form-Profiling of Optics Using the Geometry Measuring Machine and the M-48 CMM at NIST.
We are developing an instrument, the Geometry Measuring Machine (GEMM), to measure the profile errors of aspheric and free form optical surfaces, with measurement uncertainties near 1 nm. Using GEMM, an optical profile is reconstructed from local curvatures of a surface, which are measured at points on the optic's surface. We will describe a prototype version of GEMM, its repeatability with time, a measurements registry practice, and the calibration practice needed to make nanometer resolution comparisons with other instruments. Over three months, the repeatability of GEMM is 3 nm rms, and is based on the constancy of the measured profile of an elliptical mirror with a radius of curvature of about 83 m. As a demonstration of GEMM's capabilities for curvature measurement, profiles of that same mirror were measured with GEMM and the NIST Moore M-48 coordinate measuring machine. Although the methods are far different, two reconstructed profiles differ by 22 nm peak-to-valley, or 6 nm rms. This comparability clearly demonstrates that with appropriate calibration, our prototype of the GEMM can measure complex-shaped optics.
National Institute of Standards and Technology, Gaithersburg, MD 20899 USA.
Nadia
N
Machkour-Deshayes
National Institute of Standards and Technology, Gaithersburg, MD 20899 USA.
John
J
Stoup
National Institute of Standards and Technology, Gaithersburg, MD 20899 USA.
Z Q John
ZQ
Lu
National Institute of Standards and Technology, Gaithersburg, MD 20899 USA.
Johannes
J
Soons
National Institute of Standards and Technology, Gaithersburg, MD 20899 USA.
Ulf
U
Griesmann
National Institute of Standards and Technology, Gaithersburg, MD 20899 USA.
Robert
R
Polvani
asphere and free form optics; form-profilometry; optical calibration metrology; surface metrology