Detection of atmospheric carbon dioxide with air-lasing-based coherent Raman spectroscopy

Coherent anti-Stokes Raman scattering (CARS) is recognized as a powerful technique for chemical sensing, biological imaging, and combustion diagnostics, but it is rarely used in atmospheric detection due to complex multi-beam configuration and fine spatio-temporal control. Air lasing provides an attractive probe source for CARS, largely simplifying its implementation. Herein, we successfully detected atmospheric carbon dioxide (CO₂) using air-lasing-based CARS spectroscopy and quantified its concentration to be 485.5 ppm and 502.0 ppm based on two CARS signals. The measured concentrations exhibit relative errors of 0.6% and 2.7% compared to the result obtained from a commercial gas analyzer. The detection limit reaches 43 ppm, which is one order of magnitude lower than previous results. The precision exhibits a nearly quadratic decay, gradually stabilizing at a constant value as the concentration increases. The precision for atmospheric CO₂ detection ranges from 9% to 10%. The developed spectroscopy holds great potential in standoff detection of air pollutants, biological agents, and radioactive substances.