Optical precision profilometer using the differential method

A novel optical precision profilometer, which is nearly independent of vertical vibrations, is proposed. It can make simultaneous height measurements of both a measurement position and its surroundings and perform subsequent digital subtraction of the latter from the former. The noise level of this profilometer on the table with steady vibrations of 0.4 gal (1 gal = 10 (-2) m/sec(2)) is 0.05 nm root mean square. Data obtained from measurements of an optical flat and a Si wafer are included.