Optical heterodyne profilometry

TLDR

The technique is compared with existing surface‑profiling instruments. The study presents a noncontact optical profilometry method achieving ~1 Å height sensitivity. The method uses a common‑path heterodyne interferometer with orthogonally polarized, slightly frequency‑shifted beams, where the beat‑frequency phase directly encodes surface height. Measurements yield surface profiles and statistical analyses, confirming the method’s stability and repeatability.

Abstract

A noncontact optical technique for the measurement of surface profile is described, which has a height sensitivity of the order of 1 Å. It is based on a common path heterodyne interferometer in which two orthogonally polarized beams of slightly different frequency are focused on the surface to be measured. One focal point acts as a reference as the other point circularly scans the surface. The phase of the beat frequency of the interfering return beams is directly proportional to the surface height. The results of a surface measurement include graphical displays of the surface profile, autocovariance function, spectral density function, stability, and repeatability. Comparison with other instruments is also discussed.