Ultrasonic detection based on polarization-dependent optical reflection.

Owing to their extremely wide bandwidths, pure optical ultrasonic detection methods are gaining increasing interest. In this Letter, we proposed a simple ultrasonic detector that is based on the polarization-dependent optical reflection. When the acoustic wave reaches the liquid-glass interface, the acoustic pressure changed the relative refractive index between two media, leading to perturbations in the reflectance of the optical probe beam in glass. Unlike previous studies that detected the modulations in the intensity of the reflected beam, our method, named "polarization-dependent reflection ultrasonic detection (PRUD)," detects the intensity difference between two polarization components of the same probe beam. The PRUD significantly increased the sensitivity. Besides a phantom study, we also successfully detect weak photoacoustic waves in an in vivo animal experiment. This novel method can provide a simple way for ultrasonic detection, which will have great potential for ultrasound and photoacoustic imaging and sensing.