Phase unwrapping using the extracted degree of coherence and phase from phase shifting interferometry systems

Abstract

Current phase unwrapping methods for non-scanning interferometry systems with one wavelength are not robust in the presence of high steps while still having a limited step height and range using two wavelengths configurations. Here, a new phase unwrapping method is proposed, allowing imaging steps with a height up to 15 times the wavelength using one wavelength or up to 1500 times using two wavelengths. It is based on a one-time computational model fitting of calibration measurements that allows to extract the degree of coherence and phase from two phase-shifted images per wavelength, perform phase unwrapping and accurately reconstruct the 3D structure of the sample. The proposed method has a nanometric axial accuracy and can operate in real-time. The algorithms and methodology for one and two wavelengths are presented and confirmed experimentally.