Analysis of surface deformation in thin-film coatings by carrier frequency interferometry.

We demonstrate a method based on carrier frequency interferometry (CFI) that measures surface deformation with high accuracy. The method is applied to assess the deformation of thin-film dielectrics deposited on thick substrates. CFI measured the wavefront radius of curvature R with an accuracy of 0.2% for an R smaller than 500 m and 2% for an R between 500 and 2000 m (flat reference substrate). We show the method has a significantly larger dynamic range and sensitivity than Twyman-Green and comparable sensitivity to white light interferometry.