Multi-wavelengths Nonlinear Photoacoustic Imaging Based on Compact Laser Diode System

Photoacoustic imaging (PAI) combines the deep penetration of ultrasound imaging and the high absorption contrast of optical imaging, which has attracted increasing research interest in recent years. The PAI based on multi-wavelength laser source is conducive to detecting different components in the blood such as oxygen saturation. The generation of PA signals could rely on the relative low-cost pulsed laser diode. However, the multi-wavelength PAI system requires multiple pulsed laser diodes, which will multiply the cost of the imaging system. On the other hand, the amplitude of the PA signals will change when inducing the Gruneisen relaxation effect due to the heat accumulation. In this paper, we proposed a continuous multi-wavelength photoacoustic imaging (CMPAI) system based on the combination of a single-wavelength pulsed laser diode and a multi-wavelength continuous laser diode module. The continuous wave (CW) laser is adapted for heating the sample. The PA signals are induced by a single-wavelength pulsed laser. By controlling the laser irradiation sequence (pulse-CW-pulse), the images before and after heating will be attained. By proper differentiating operations, the images with different-wavelengths' light absorption could be revealed. Furthermore, using this proposed system to detect the concentration of ink that is mixed by different portion of green and red ink would be demonstrated in the following.