a State Key Laboratory of High Field Laser Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800, China
b University of Chinese Academy of Sciences, Beijing 100049, China
c School of Physical Science and Technology, ShanghaiTech University, Shanghai 200031, China
d School of Science, East China University of Technology, Nanchang 330013, China
Funds:
Program of Shanghai Academic Research Leader (20XD1424200)
Shanghai Municipal Science and Technology Major Project (2019SHZDZX01)
This work is supported by the National Natural Science Foundation of China (11822410, 12034013, 12074063)
and Youth Innovation Promotion Association of CAS (2018284).
Key Research Program of Frontier Sciences of Chinese Academy of Sciences (QYZDJ-SSW-SLH010)
Remote or standoff detection of greenhouse gases, air pollutants, and biological agents with innovative ultrafast laser technology attracts growing interests in recent years. Hybrid femtosecond/picosecond coherent Raman spectroscopy is considered as one of the most versatile techniques due to its great advantages in terms of detection sensitivity and chemical specificity. However, the simultaneous requirement for the femtosecond pump and the picosecond probe increases the complexity of optical system. Herein, we demonstrate that air lasing naturally created inside a filament can serve as an ideal light source to probe Raman coherence excited by the femtosecond pump, producing coherent Raman signal with molecular vibrational signatures. The combination of pulse self-compression effect and air lasing action during filamentation improves Raman excitation efficiency and greatly simplifies the experimental setup. The air-lasing-assisted Raman spectroscopy was applied to quantitatively detect greenhouse gases mixed in air, and it was found that the minimum detectable concentrations of CO2 and SF6 can reach 0.1% and 0.03%, respectively. The ingenious designs, especially the optimization of pump-seed delay and the choice of perpendicular polarization, ensure a high detection sensitivity and signal stability. Moreover, it is demonstrated that this method can be used for simultaneously measuring CO2 and SF6 gases and distinguishing 12CO2 and 13CO2. The developed scheme provides a new route for high-sensitivity standoff detection and combustion diagnosis.