Coherent anti-Stokes Raman spectroscopy enhanced by multiple overtone resonances

We report a novel approach to coherent anti-Stokes spectroscopy based on multiple overtone resonances in both theory and experiment. A pump laser with the tunable wavelength at the near infrared range is used to excite the inner-band vibrational transition of the C-H stretching vibrations, commonly corresponding to biological molecules. Strong coherent signals with higher chemical specificity are observed in experiments. Our work points to a new route for applying resonantly enhanced nonlinear optical spectroscopy in the deeper tissue optical imaging with near infrared lasers, which is important for various biomedical applications.