Three-dimensional spatial coherent imaging based on two-dimensional laser ultrasonic row-column addressing array

Three-dimensional (3D) imaging represents a crucial advancement in ultrasonic non-destructive testing (NDT). Compared with one-dimensional (1D) arrays, full matrix capture (FMC) based on two-dimensional (2D) arrays experiences exponential growth in required elements and sampling channels, fundamentally constraining array aperture and imaging resolution. The row-column addressing (RCA) array innovatively reduces the element count from N × N to N + N through alternating row-column addressing, significantly decreasing channel requirements and sampling data volume. This study pioneers a fully optical approach for 2D RCA array, aiming to achieve 3D non-contact imaging of body defects. Methodologically, the research progresses through three phases: First, to generate uniform energy cylindrical waves, an optical modulation technique was developed to create elongated homogenized laser spots, enabling laser ultrasonic orthogonal compound scanning for array data acquisition. Second, a 3D spatial coherence imaging algorithm was established for multimode characterization of artificial blind holes and simulated corrosion defects. Finally, systematic comparisons of several array configurations and imaging algorithms were conducted, with optimization strategies analyzed. Experimental results demonstrate that laser ultrasonic RCA array imaging effectively reconstructs 3D defect geometries and dimensional features. Multimode visualization successfully resolves geometrical variations across defect regions. This work introduces a novel non-contact array inspection methodology, facilitating the transition from 2D to 3D in ultrasonic NDT. The findings provide critical insights into adaptive algorithm selection and system optimization for high-resolution volumetric inspection.