Investigation of Underwater Ultrasonic Imaging Methods Based on Acousto-Optic Holography

This study presents a high-density underwater acoustic field sensing and imaging method based on optical heterodyne interferometry. By analyzing phase modulation induced by acoustic perturbations, the system enables non-contact acoustic field reconstruction. A high-sensitivity phase demodulation scheme using Hilbert transform achieves a detection sensitivity of ~0.1 V/Pa. The envelope correlation coefficient with hydrophone signals reaches 0.955 and remains above 0.95 under microwatt-level laser power. For acoustic field imaging, a holographic model combining tomographic scanning and angular spectrum propagation reconstructs spatial distributions with a normalized mean square error of 0.042. Successfully achieved holographic imaging of a "U"-shaped obstacle, with spatial feature reconstruction error below 5%. To improve resolution, a Taylor expansion-based field extrapolation algorithm is introduced, forming a virtual aperture that extends the spatial sampling range by 13%–40%. This method offers high-resolution imaging of weak acoustic fields, with promising applications in medical, nondestructive, and underwater imaging.