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Processing of white-light correlograms: simultaneous phase and envelope measurements by wavelet transformation

A common procedure of profilometry by means of white light interferometry is to scan one interferometer arm step by step. In this way, the intensity detected for each surface point reproduces the autocorrelogram of the light source, which is used for the determination of the absolute phase between a reference position and the zero optical path difference position. Phase changes due to reflection on the inspected surface produces a shift of the interference fringes with respect to the coherence envelope. If those phase changes vary from points to points, artifacts can be introduced in the profile reconstruction. We propose to measure simultaneously the interferometric phase and the shift of the interference fringes with respect to the coherence envelope. That processing is based on a wavelet transformation of the sampled light source correlograms and leads to complementary information that describes more completely the optical behavior of surfaces.