A SOLUTION TO THE PROBLEM OF STATIONARY-PHASE IN DOUBLE SPECTRAL MODULATION PROFILOMETRY

A solution to a problem frequently found in interferometric surface profilers working with spectral modulation is presented. The phase of the signal which stores the surface profile depends both on the surface depth and on the wavenumber. In those regions where the phase function reaches an extreme value (stationary phase points) phase determination from intensity measurements is not possible. A procedure which overcomes this problem is presented: two recordings of the interference pattern are required; the second one is recorded after the introduction of an (arbitrary) additional path difference. The method is self-contained in the sense that no piezoelectric transducers, nor calibrated mirror shifts are required.