Optical EngineeringFull-field heterodyne interferometer for shape measurement: experimental characteristics of the system
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Heterodyne interferometry is a powerful tool for shape measurement. However, there are currently only few papers devoted to full-field, time-dependent heterodyne interferometry. Most known solutions are based on the point measurement, and the shape is obtained by scanning in the examined area. We propose and discuss a full-field heterodyne system using the fringe projection principle and a fast framing Dalsa CA-D1 CCD camera. Due to the frequency shift between interfering beams, the interference pattern travels over the object surface and enables heterodyne registration. The use of a fast camera is a certain approximation of classical heterodyne detection. Quantitative analysis of the influence of some system parameters (geometry, elements, and optical system aberrations) on the measurement result for a chosen object is the basis for developing a final system able to measure two kinds of surfaces: the scattering and specular types. A complete optical system and the geometry of the field heterodyne interferometer realized in the laboratory are shown and discussed. Examples of results obtained are presented, including shape measurement during object movement.