Dual-Channel Laser Speckle Interferometry for the Simultaneous Measurement of Surface Deformation and Its Slope

Speckle interferometry, as a high-precision, non-contact, and highly sensitive optical non-destructive testing method, has been widely applied in fields such as defect detection, quality control, and mechanical deformation analysis of materials. Due to its technical characteristics, speckle interferometry can directly measure the out-of-plane displacement of the tested object or the slope along the shear direction. However, for the simultaneous measurement of out-of-plane displacement and its slope, speckle interferometry and shear speckle interferometry still have limitations in aspects such as time-frequency characteristic analysis and branch coupling methods. To address this, this paper proposes a fiber-optic coupled holographic-shear dual-channel speckle interferometry phase measurement technique, utilizing Fourier transform for phase retrieval to detect out-of-plane displacement and its slope information on the material surface during deformation. Experimental results demonstrate that the system has the capability for quantitative measurement of out-of-plane displacement and its slope, with a relative error of 3.75% for the measured out-of-plane displacement and an error of 1.61% for the slope.