Full field, time dependent heterodyne interferometer for shape measurement: theory and experiment

摘要

Heterodyne interferometry is a powerful tool for shape measurement. However, to the present day there are only few papers devoted to full field, time dependent heterodyne interferometry. Most of known solutions are based on the point measurement, and the shape is obtained by scanning in the examined area. In this paper a full field heterodyne system using the fringe projection principle and fast framing DALSA CA-D1 CCD camera is proposed and discussed. Due to frequency shift between interfering beams the interference pattern is travelling over the object surface and allows heterodyne registration. The use of a fast camera is a certain approximation of classical heterodyning. The paper presents the measurement method, some theoretical considerations and results obtained by computer simulations. Quantitative analysis of the influence of some system parameters (geometry, elements, and optical system aberrations) on the measurement result for a chosen object was the base for developing the final system stand able to measure two kinds of surfaces, i.e. he rough and mirror type ones. A complete optical system and geometry of the field heterodyne interferometer realized in laboratory are shown and discussed. Examples of obtained results are presented including shape measurement during object movement.