Simultaneous Measurement of In-Plane and Out-of-Plane Deformations Using Dual-Beam Spatial-Carrier Digital Speckle Pattern Interferometry

Digital speckle pattern interferometry (DSPI) is an advanced technique for both in-plane and out-of-plane deformation measurements of diffuse surfaces in nanoscale. It has been widely used in aerospace engineering and other high-tech industries due to the advantages of non-contact, high-accuracy and full-field measurement. Traditionally, DSPI uses temporal phase shifting method to achieve precise deformation measurement, but it is only suitable for quasi-static deformation. Spatial-carrier method is another effective phase retrieval method used in DSPI and its validity has been verified in some DSPI setups. DSPI with spatial-carrier method enjoys the advantages of simple optical arrangement, easy operation, and above all, high-speed measurement of deformation. This paper introduces a dual-beam spatial-carrier digital speckle pattern interferometry system, with which in-plane and out-of-plane deformations can be measured simultaneously as well as quickly. In the optical setup, two lasers are employed to illuminate the measured object with different illumination angles, and two single-mode fibers server as carriers to transmit the reference beams. In-plane and out-of-plane deformations can be obtained by combining the phase maps of both channels. Theoretical discussion and experimental analysis are both presented.