Differential optical profilometer using a single probe beam

This paper describes a heterodyne common path differential phase interferometer which is resistant to the thermally and microphonically induced measurement errors of non-common path systems. The system utilizes a single probe beam which is focused onto the sample and then imaged onto the detector plane. Differentiation in any direction can be performed by altering the positions of the detectors. A theoretical derivation of the system transfer function is presented, the results from which show excellent agreement with experimental measurements. Initial theoretical results of the recovery of a sample profile from its differential profile are presented. Finally, a simplified and more stable differential system is introduced.