Ultrasonic imaging modalities enabled by laser diffuse ultrasonic phased arrays

To perform a full matrix capture (FMC) with a laser-induced ultrasonic phased array, both the generation and detection lasers must be independently scanned to acquire signals from all combinations of source and receiver positions. In contrast, a laser diffuse ultrasonic phased array (LDUPA) enables rapid acquisition of an equivalent FMC dataset by scanning only a detection laser while ultrasound is generated from a fixed transducer. This FMC dataset is subsequently reconstructed by applying a diffuse correlation technique to the raw receive dataset. While the reconstructed FMC dataset is used for total focusing method (TFM) images, the early, coherent raw receive dataset can also be used directly to form images via a receive-only focusing method (RFM). This study compares ultrasound images generated from both the raw receive datasets and the reconstructed FMC datasets across various inspection configurations, including different transmitter positions and incident wave angles. Results from simulations and experiments show that the RFM images exhibit excellent detection capability within the incident wave’s illumination area, providing 2–5 dB higher signal to peak noise ratio compared to TFM images. In contrast, TFM images demonstrate good detection across the entire receiver aperture. The results also highlight the flexibility in transmitter positioning and incident wave angle, facilitating inspections that can adapt to accessibility constraints.