Fig. 1: Basic principle of SS-CRS thermometry based on optically induced air lasing.

a Schematic of basic processes of SS-CRS thermometry based on air lasing. b Temporal envelope of \({{\rm{N}}}_{2}^{+}\) lasing and the delay of lasing emission with respect to the pump laser. The inset shows the spatial profile of the \({{\rm{N}}}_{2}^{+}\) lasing. c Energy-level diagram of rotational coherent Stokes Raman scattering (RCSRS). \({\omega }_{p}\), \({\omega }_{{as}}\), \({\omega }_{{pr}}\), and \({\omega }_{{CSRS}}\) represent, respectively, the angular frequencies of the pump, the anti-Stokes, the probe and the CSRS fields. \(\varOmega\) represents the frequency difference between the pump and anti-Stokes fields. The incident pump laser provides both the pump and anti-Stokes fields, whereas the \({{\rm{N}}}_{2}^{+}\) lasing serves as the probe field. d The typical RCSRS spectrum measured in \({{\rm{O}}}_{2}\) at room temperature. In order to measure the air lasing and RCSRS signal simultaneously, a filter was used to attenuate the air lasing signal in the data acquisition. Each spectral line is labeled by the rotational quantum number of lower state (\(J\)) in the corresponding Raman transition (\(J+2\to J\))