PROFILOMETRY BY ZERO-ORDER INTERFERENCE FRINGE IDENTIFICATION

In white light interferometry, the visibility of the fringes is direct ly related to the optical path difference between the two interfering beams. With a very short coherence length light source, the zero-order interference fringe may be detected by a simple maximum intensity loc ation while the reference mirror is shifted by a piezoelectric transdu cer. We use this possibility for high-resolution profilometry. We disc uss the maximum sampling distance, which guarantees a correct detectio n, as a function of the self coherence function of the light source. A practical configuration based on Mirau interferometric microscope obj ective was built. The experimental results show the nanometric resolut ion of this technique and its ability to profile surfaces with sharp s lopes and deep holes. The application field of either heterodyne or co nfocal profilometers may be extended by associating them with the prop osed method.