White-light interference demodulation algorithm based on SVMD-HD denoising

Vertical-scanning white light interferometry (VSWLI) is a non-contact three-dimensional surface profile measurement method. As an inherent defect in VSWLI, the batwings are especially significant at the step edge when the step height of the measured sample is smaller than the coherent length of the light source. The phase-shifting interferometry does not suffer from it, but has phase ambiguity problems. A white-light interference demodulation algorithm that combined Carré equal-step phase-shifting algorithm with fast Fourier transform (FFT) coherence-peak-sensing technique was proposed to overcome the above problems. This algorithm was based on successive variational mode decomposition (SVMD) combined with Hausdorff distance (HD) denoising. The continuous step devices at 500 nm and 1 200 nm height and the standard steps at 10 μm height were used as test samples for verification of experimental measurements. The proposed algorithm can effectively suppress the batwings effect at the step edges and remove the phase-ambiguity problems.