Virtual Acoustic Detector Arrays for All-Optical Ultrasound Sensing

We introduce a compact, non-contact multimodal imaging platform that integrates ultrasound ( US) imaging, inclusive of photoacoustic (PA) detection, with optical coherence tomography (OCT). This integration is achieved through a novel virtual acoustic detector array (VADA) technique for all-optical US sensing, utilizing the temporal and spatial resolving capabilities of swept-source optical interferometry. The technique extracts US signals from the phase time evolution of a swept-source OCT's spectral sweep. It enables the virtual construction of the VADA along both lateral and depth directions on the imaging target for non-contact detection of acoustic waves from surrounding US sources. The platform's high-speed scanning (MHz OCT A-scan rate) and ultra-sensitive phase detection (nm displacement sensitivity) allow for the customization of the spatial density of the VADA and the collection of wideband acoustic signals, which are essential for the reconstruction of US images. In our pilot study, we successfully demonstrated the feasibility of this technique. We used a conventional US transducer as an acoustic source. The acoustic field distribution within the imaging target and the morphology and position of the piezoelectric layer were successfully reconstructed, which is based on US waveforms obtained from the VADA.