In fast functional photoacoustic microscopy (FPAM), the detection and monitoring of the oxygen saturation are important to monitor tissue functionality and disease progress. FPAM needs multi-wavelength pulsed laser sources with high pulse repetition rates, sufficient pulse energies and short wavelength switching time. Here, we develop a multi-wavelength pulsed laser source based on the stimulated Raman-scattering effect. The new laser is based on a 532-nm 1-MHz pulsed laser. The 532-nm laser pulse is split into two beams: one pumps a 5-m optical fiber to excite a 558-nm wavelength via stimulated Raman scattering; the other one propagates through a 50-m optical fiber to delay the pulse by 220 nano second so that the excitation wavelengths can be separated in time for fast functional photoacoustic imaging. The two beams are spatially combined and coupled into an optical fiber for photoacoustic excitation. Consequently, the new laser source can generate 2 million pulses per second, switch wavelengths in 220 ns, and provide hundreds of nano-Joules pulse energy for each wavelength. Using this laser source, we demonstrate optical-resolution photoacoustic imaging of microvascular structure and oxygen saturation in the mouse ear. The ultrashort wavelength switching time enables oxygen saturation imaging of flowing single red blood cells.
Chao LIU, Yizhi Liang, Long Jin, Bai-Ou Guan, and Lidai Wang, "A short switching time pulsed laser for functional photoacoustic microscopy (Conference Presentation)," Proc. SPIE 10494, Photons Plus Ultrasound: Imaging and Sensing 2018, 104942K (Presented at SPIE BiOS: January 31, 2018; Published: 15 March 2018); https://doi.org/10.1117/12.2288883.5752218908001.
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