Abstract: Compound surfaces of a test object are interferometrically measured by a multi-beam probe. One of two measuring beams emerges from the probe at a fixed angle for measuring one of the compound surfaces, and the other measuring beam emerges from the probe at a variable angle for measuring a plurality of other compound surfaces.

Abstract: A scanning interferometer employs dual interferometer modules at different wavelengths to expand a dynamic range of measurement, a compound probe for measuring multiple surfaces, and a confocal optical system for distinguishing between the surfaces measured by the compound probe. Within the compound probe, miniature optics divide a test beam into two sub-test beams that are focused normal to different test surfaces. Both sub-test beams contain the different wavelengths. A separate interferometer monitors movements of the compound probe for producing absolute measures of the test surfaces.