Electronic-Resonance-Enhanced Coherent Raman Spectroscopy with a Single Femtosecond Laser Beam

Coherent Raman scattering (CRS) spectroscopy holds versatile applications in many fields ranging from measuring temperature and concentration in reacting flows to imaging biological molecules in living cells. Although the powerful spectroscopic technique has been studied for a few decades, significant attention is still paid to developing state-of-the-art CRS spectroscopy with the simpler design and higher sensitivity for practical applications in harsh or complex environments. Herein, a novel electronic-resonance-enhanced coherent Raman scattering (ERE-CRS) technique is developed with a single femtosecond laser beam. Such single-beam ERE-CRS scheme is accomplished with the narrowband air lasing signal naturally generated in the interaction region as a probe source. The developed technique not only avoids fine spatio-temporal control in the conventional multibeam configuration, but also accomplishes 1-2 orders of magnitude enhancement of 12CO2+${}<^>{12}{\mathrm{CO}}_{2}<^>{+}$ Raman signal due to the resonance of air lasing with electronic transition of the target gas. The dramatic enhancement effect is also manifested through the comparative measurements in CO2 isotopes. The single-beam ERE-CRS spectroscopy shows an unprecedented opportunity for the high-sensitivity standoff detections of gas-phase molecules and plasmas.