Two-wavelength full-field heterodyne interferometric profilometry

Abstract

An alternative full-field interferometric profilometry is proposed by combining two-wavelength interferometry and heterodyne interferometry. A collimated heterodyne light is introduced into a modified Twyman–Green interferometer, the full-field interference signals are taken by a fast CMOS camera. The sampled intensities recorded by each pixel are fitted to derive a sinusoidal signal with the least-square sine wave fitting algorithm, and its phase can be obtained. Comparing the phase of the reference point, the relative phase of the pixel can be calculated. Next, the same measurement is made again at a different wavelength. The relative phase with respect to the effective wavelength can be calculated and the profile of the tested sample can be derived with the two-wavelength interferometric technique. Its validity is demonstrated. It has merits of both two-wavelength interferometry and heterodyne interferometry.