Single‐Beam Coherent Raman Spectroscopy Enabling Multispecies Detection With ppm‐Level Sensitivity

Simultaneous, sensitive detection of multiple molecular species is of great significance for environmental monitoring, chemical reaction tracking, and combustion diagnostics; however, achieving this goal using a single laser beam remains challenging. Herein, based on cascaded amplified air lasing, we develop a single‐beam coherent Raman spectroscopy that enables multispecies detection with ppm‐level sensitivity. The cascaded focusing scheme simultaneously enhances air lasing energy, compresses its pulse duration, and broadens the pump laser spectrum, thereby substantially improving the efficiency of coherent Raman scattering. Compared with a single focusing geometry, the quadruple‐pass focusing scheme enhances the SF 6 Raman signal by nearly three orders of magnitude, resulting in nearly 30‐fold reduction in the limit of detection (LOD). Using this spectroscopy, we quantitatively measure six greenhouse gases and pollutants: SF 6 (LOD = 16.3 ppm), C 2 F 6 (28.6 ppm), CF 4 (30.9 ppm), SO 2 (33.5 ppm), N 2 O (72.1 ppm), and CO 2 (103.2 ppm). This spectroscopy also exhibits high precision and the ability of multispecies simultaneous detection. This study advances the application of air lasing and establishes a versatile spectroscopic platform for quantitative multi‐component gas analysis.