Interferometric measurements of the surface profile of moving samples.

An acoustooptic cell frequency-shifts 632.8-nm radiation reflected off moving low-reflectivity surfaces. Surface asperities produce phase shifts in an 80-MHz carrier frequency. Surface profile plots and quality parameters are obtained by analyzing digitized phase shifts. Rigid samples may be turntable mounted, and flexible web samples are moved over a smooth stationary guide. A spatial resolution of 1 μm and a vertical resolution of 1 nm are obtained. Reproducibility of rms measurements is also within 1 nm.