Confocal operation in differential phase interference microscopy

This paper discusses the operation and imaging properties of various types of optical heterodyne interferometer. Conditions needed to achieve confocality in differential interference microscopes are considered. This leads to a novel extended focus phase imaging mode. Results are presented which demonstrate this mode of operation and show the ability of the technique to produce accurate phase measurement on samples with warp and tilt, over a range much greater than the depth of focus of the objective lens.