A phase-sensitive optical heterodyne interferometer for surface height measurement

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Abstract
A phase-sensitive scanning optical microscope is described which can measure surface height changes of less than 3 ångströms. The system is based on a heterodyne version of the Michelson interferometer, and has been designed to reject phase noise caused by vibration in the optics and the sample. A specially constructed objective lens is used to direct two laser beams on to the object surface. The first beam forms a tightly focused spot to probe the sample structure, and the second remains collimated, acting as a large-area on-sample reference beam.