18-Tutorial 3a

BY ROBERT SMYTHE, ZYGO CORP.forMEASUREMEASUREInstantaneous phase-measuring interferometry provides production-level provel metrology.hase-measuring interferometry (PMI) is the metrolo- PMI—to measure these phase differences. The classic PMIgy tool of choice for the optical industry, measuring technique, phase-shifting interferometry (PSI), uses multi-Pkey parameters such as surface figure, transmitted ple frames of data acquired in sequence while shifting thewavefront, homogeneity, and radius of curvature for process phase. Phase shifting is performed through either mechan-control and quality assurance. Previously confined to the ically changing the length of the interferometer cavity orquality-control laboratory, PMI has become necessary tech- by changing the wavelength during data acquisition suchnology for monitoring surface figure and transmitted wave- as wavelength specific PSI (WSPSI). Both PSI approachesfront on the production floor. Manufacturing tolerances for provide very low measurement uncertainty. optical components as diverse as cell phone lenses and large Recently, new techniques have been invented fortelescope mirrors require interferometric-level metrology in enhanced performance: Fourier-transform PSI, for measur-environments in which low-noise testing facilities are ing multiple surfaces, and IPMI, for data acquisition in pro-1impractical. New instantaneous PMI (IPMI) techniques duction environments. We are going to focus on the ...