Improvement of three-dimensional laser diffuse ultrasonic phased array imaging via signal amplitude compensation and reception sampling optimization

The laser diffuse ultrasonic phased array technique, which integrates a conventional piezoelectric transducer as a transmitter with a laser interferometer as a receiver and array data reconstruction technique, offers an efficient approach for imaging volumetric defects. However, time-domain amplitude decay of the acquired raw signals degrades the quality of the reconstructed array data and subsequently impairs imaging performance. In this study, an amplitude compensation method is proposed to improve data quality and enhance the resulting ultrasound images for defect detection. To further enhance inspection efficiency, square-shaped, hexagonal-shaped, and Poisson-disk reception sampling layouts are optimized to reduce the number of sampling points without compromising image quality. The proposed workflow is validated using both simulated and experimentally measured data, as evidence by more than 2 dB improvement in the signal to noise ratio of defect images and relaxation of the reception sampling pitch to one wavelength. This study provides a foundation for more robust and efficient laser-based ultrasonic imaging in real-world non-destructive evaluation applications.