Recently, a novel pure optical acoustic detection method was developed by Prof. Changhui Li’s lab in College of Engineering (COE), Peking University. They also successfully used this method to perform high resolution mouse ear imaging in vivo. The result was published in Optics Letters entitled “Ultrasonic detection based on polarization-dependent optical reflection”. The corresponding author is Prof. Changhui Li. The first author is Xiaoyi Zhu, a PhD student in COE, Peking University.
Ultrasonic detectors with broad-band, small size, and high sensitivity are highly desired for both ultrasound imaging and the emerging photoacoustic tomography (PAT). Although various kinds of piezoelectric-material-based ultrasound transducers have been commercially available and widely used, these transducers generally have limited bandwidths (centered at their resonant frequency), and the electrical noise significantly increases as the transducer becomes smaller. Therefore, various pure-optical ultrasonic detectors have gained increasing interest due to their superior wide bandwidths and small effective active sizes, as well as high sensitivity. While, most of sensitive optical methods require challenging specially customized components (micro-ring, Fabry-Perot film, etc), which limit their broad implementations.
Among pure optical methods, one of the simplest is based on the modulations of light reflectivity at an interface due to the refractive index variations caused by the ultrasonic pressure. Because of the laser instability, spontaneously environmental variation, as well as the electrical noise background from the detector, the minimum pressure it can detect is in the order of 1 bar (106Pa), limiting its biomedical implementations. Prof. Changhui Li’s group successfully developed the so called “Polarization-dependent Reflection Ultrasonic Detection” (PRUD), which is based on the detection of the intensity difference between two polarization components of the same probe beam that is reflected on the inner surface of a transparent prism. PRUD employs the balanced detection methods, which effectively suppresses much of the unwanted noise signal, substantially increases the detection sensitivity. They have achieved the noise equivalent pressure to be 1.7kPa, and this can be further improved. In addition, PRUD also has a flat and wide bandwidth from almost zero to over 100MHz. With this superior detector, they performed a mouse ear in vivo photoacoustic microscopy study. This method is so simple that it can be feasibly built in most of the optics labs. Their study will attract both researchers and engineers in optical and ultrasound fields. Next, Prof. Li’s group will continue improving the sensitivity and stability and integrate it with other modalities.
Prof. Li’s group (http://bme.pku.edu.cn/otlab) is devoted to the development and implementation of novel biomedical optical imaging methods. Their major research fields include: photoacoustic tomography, fluorescence molecular tomography, and multimodal molecular imaging.