Measuring phase dispersion of dielectric multilayer stacks

Superposition-fringes interferometry is a valuable tool to detect the phase dispersion of highly reflecting semitransparent layers. Phase dispersion shows as a fringe deviation of spectrally dispersed fringe patterns. If the fringes are spectrally dispersed, the zero optical path difference fringe should be straight and run parallel to the edge of the spectrum with white-light illumination. This is not the case with dielectric films. These phase deviations give rise to measurement errors in interferometry in general. Here the equation for the superposition fringes is given together with a few measuring examples. Automated evaluation and calibration posibilities are discussed and limitations of the measuring method are outlined.