Dynamic measurement of three-dimensional absolute displacements using dual-camera multiplexed digital holography

Digital holography has been frequently used to measure the micro-deformation in mechanical tests due to its full-field measurement with high resolution and accuracy. To measure dynamic three-dimensional absolute displacements without a known reference displacement, a new technique based on the combination of off-axis multiplexed digital holography and stereo photogrammetry is proposed. Under the illumination of two different wavelength lasers along various directions, two off-axis multiplexed holograms recorded by the dual-camera system are used to extract four phase maps with different sensitivity vectors simultaneously. Meanwhile, the variation of sensitivity vectors and registration of phase maps are carried out by the object shape measured by the dual-camera system. By the four registered phases with four varying sensitivity vectors, three-dimensional absolute displacements can be determined. The feasibility of our method is well demonstrated by a quantitative experiment and finite element analysis, and the dynamic measurement of a resistor undergoing thermal expansion is presented.