Photoacoustic computed tomography with lens-free focused fiber-laser ultrasound sensor

Optical detection of ultrasound is attractive to photoacoustic imaging due to its high sensitivity per unit area, broad bandwidth, and electromagnetic immunity. To enhance the sensitivity, previous optical transducers commonly necessitate bulk acoustic lenses to achieve focused ultrasound detection. Here, we proposed and demonstrated a novel lens-free focused optical ultrasound sensor by mechanically bending a flexible fiber laser. At a curvature radius of 30 mm, the curved fiber laser well conformed to the spherical wavefront of ultrasound exhibiting ~5 times higher sensitivity compared with the straight one. The focused fiber laser ultrasound sensor (FUS) presented a minimum detectable pressure of ~36 Pa with a working distance equal to its curvature radius. The sensor was applied to circular scanning photoacoustic computed tomography (PACT), which showed a ~70 μm in-plane resolution and a ~500 μm elevational resolution. In vivo imaging of a zebrafish and mouse brain shows the potential of this focused FUS for photoacoustic imaging in biological/medical studies.