High-Sensitivity Gas Detection with Air-Lasing-Assisted Coherent Raman Spectroscopy

Remote or stando ff 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 speci fi city. 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 fi lament 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 e ff ect and air lasing action during fi lamentation improves Raman excitation e ffi ciency and greatly simpli fi es 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 CO 2 and SF 6 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 CO 2 and SF 6 gases and distinguishing 12 CO 2 and 13 CO 2 . The developed scheme provides a new route for high -sensitivity stando ff detection and combustion diagnosis.