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

Abstract

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.

Measurement of Carbon Dioxide Isotopes with Air-Lasing-Based Coherent Raman Spectroscopy

“…It usually requires the complex spectral compression technique in order to acquire such a narrow-band ps probe from the fs pump. , The air lasing driven by strong laser fields provides an ideal candidate as the probe of CRS due to its intrinsically narrow spectrum, good directionality, unique spatiotemporal characteristics, and abilities of cavityless amplification and on-site generation in open air. − Unlike other secondary radiation induced by femtosecond lasers, the spectral bandwidth of air lasing can be as narrow as a few inverse centimeters, facilitating the identification of different species and even isotopic molecules. In past years, various air-lasing-based Raman spectroscopies have been developed. − In 2022, Zhang et al performed a proof-of-principle experiment on gas sensing and isotope identification with air-lasing-based CRS spectroscopy . Although the great potential of the novel spectroscopic technique for isotope detection has been verified, quantitative measurement has never been explored.…”