Hybrid multi-wavelength nonlinear photoacoustic sensing and imaging.

Multi-wavelength photoacoustic (PA) imaging has been studied extensively to explore the spectroscopic absorption contrast of biological tissues. To generate strong PA signals, a high-power wavelength tunable pulsed laser source has to be employed, which is bulky and quite expensive. In this Letter, we propose a hybrid multi-wavelength PA imaging (hPAI) method based on the combination of a single-wavelength pulsed laser source and multi-wavelength continuous-wave (CW) laser sources. By carefully controlling the laser illumination sequence (pulse-CW-pulse) and extracting the PA signal difference before and after the heating of CW lasers, the optical absorption property of multi-wavelength light illumination could be obtained. Compared with conventional PA imaging, the proposed hPAI shows a much lower system cost due to the usage of single-wavelength pulsed lasers and multiple inexpensive CW lasers. As the preliminary results show in this Letter, hPAI imaging has the potential to provide another pathway for high spectroscopic optical absorption contrast in PA imaging.