Non-contact ultrasound imaging based on sub-terahertz photoacoustic effect and laser vibrometry

Ultrasound imaging is a widely used technique for non-destructive testing and in vivo inspection. However, conventional ultrasound imaging relies on contact-based transducers to generate and detect signals, limiting the applicability of the ultrasound. In this study, we propose an approach to implement fully non-contact ultrasound imaging based on the sub-terahertz photoacoustic effect and laser Doppler vibrometry. Compared to infrared pulse-based laser ultrasound systems, the use of continuous sub-terahertz waves enables ultrasound generation through opaque materials, such as clothing and plastics, and offers further prospects of system integration based on solid-state electronics. We demonstrate that the system can detect minute changes in resonance frequency across different media and is capable of tracking multiple ultrasound reflections through inverse Fourier transform. Furthermore, we present a result of raster scan imaging, showcasing the capability of the system for non-contact ultrasound imaging.