SNR-enhanced fiber-laser ultrasound sensors for photoacoustic tomography*

Optical detection of ultrasound for photoacoustic imaging has received great interest. Recently, we have developed a new fiber-optic ultrasound sensor by exploiting dual-polarization fiber laser. It offers high sensitivity (40 Pa over 50 MHz) as well as good stability as a result of the self-heterodyning detection. In this work, the signal-to-noise ratio has been enhanced by suppressing the noise of the ultrasound sensing system via signal averaging. As a result of multiple measurements of a single photoacoustic signal, the total noise was reduced by 40%. With the enhanced detection capability, the sensors have been deployed as photoacoustic probes in different imaging modalities. We demonstrate fastscanning photoacoustic microscopy with a field-of-view 2×2 mm2, a frame rate of 2 Hz to visualize the blood flow dynamics. By bending the flexible fiber optic sensor for geometrical focusing, PACT was realized to image a mouse brain with a spatial resolution of 70 μm. An all-fiber photoacoustic endoscope was built to in vivo image the vascular network of a rat rectum, with a lateral resolution of 10 μm, with a 2.3-mm probe diameter.