Stimulated Raman scattering (SRS) microscopy generates chemical maps of live cells or tissues. A handheld imaging system using an optical fiber for laser delivery further enables in situ and in vivo measurements. However, the non-resonant background caused by the interaction between two ultrafast pulses inside an optical fiber overwhelms the stimulated Raman signal from the sample. Here, we report a background-free handheld SRS microscope. By temporally separating the two ultrashort pulses propagating in the fiber and then overlapping them on a sample through a dispersive material, we detected stimulated Raman signal that is 200 times weaker than the non-resonant background. The handheld microscope allowed ambient-light mapping of pesticide on a spinach leaf, cancerous tissue versus healthy brain tissue in a canine model, and cosmetic distribution on live human skin.
Ji-Xin Cheng and Chien-Sheng Liao, "In vivo and in situ spectroscopic imaging by a handheld stimulated Raman microscope (Conference Presentation)," Proc. SPIE 10489, Optical Biopsy XVI: Toward Real-Time Spectroscopic Imaging and Diagnosis, 104890R (Presented at SPIE BiOS: January 31, 2018; Published: 14 March 2018); https://doi.org/10.1117/12.2284255.5751463294001.
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