Analysis of Fizeau wedge with a non-air gap by plane wave expansion

The optical interferential wedge or Fizeau wedge (FW) is a useful optical element with various applications in optical metrology, spectroscopy and laser technique. Various FW applications require knowledge of its response to illumination by a laser beam with an arbitrary wavefront. Recently, we applied the plane wave expansion method to study transmission and reflection of an air-gap FW under illumination with a Gaussian beam. The approach is based on the angular spectrum of the beam and the known FW response to illumination with a plane wave. In this study, we adapt this approach for the more general and more frequently encountered case of a FW with a non-air gap. We developed an approximate algorithm, which is applicable at small incidence angles to wedges with refractive indices different from 1 and illuminating beams with arbitrary amplitude and phase distributions. Comparison to the experiment is also provided.