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To improve the excitation efficiency, detection utilisation rate, and signal-to-noise ratio of the laser ultrasonic non-destructive testing of internal defects, the spatial distribution of the excitation light source was changed to a ring-shaped laser source to excite ultrasound. Finite element analysis method was used to simulate and analyse the ultrasonic characteristics excited by the ring laser. The superposition of shear waves on the central axis of a ring laser exhibits considerable advantages for internal defect detection. Consequently, a method was proposed for detecting internal defects using a ring laser to excite and receive ultrasonic waves at the concentric and opposite positions of the ring laser. A ring-source laser ultrasonic detection system was designed to scan and detect circular hole defects with different diameters as well as crack defects with different depths, lengths, and inclination angles. The experimental results showed that the ring-source laser ultrasonic technique could effectively detect defect positions and depths and describe the defect length and external contour under certain conditions. Moreover, it could achieve more complex detection tasks. This study provides an effective reference for the application of laser ultrasonic non-destructive testing of internal defects. [ABSTRACT FROM AUTHOR]

A dynamic holographic vibration measurement system based on a photorefractive crystal of BSO in diffuse mode without the need for an external electric field, which allows for simultaneous measurement of in-plane and out-of-plane high-frequency vibrations, is studied theoretically and experimentally in this work. By adjusting the polarization state of the reference beam, the system introduces a necessary additional phase shift of π/2 to achieve highly sensitive and linear demodulation of small phase-to-intensity vibration signals. Both theoretical analysis and experimental results confirm the system's practicality and safety, demonstrating its ability to accurately detect vibrations without the risks associated with high-voltage drift mode operation. Furthermore, some factors that affect measurement sensitivity were analyzed. The results of measuring in-plane and out-of-plane vibrations showcase the system's superior performance in measuring submicron magnitude vibrations at the MHz level.