Fig. 1. The luminous distribution of near-concentric cavities and DNCCG. (a) Near-concentric cavity A; (b) near-concentric cavity B; (c) DNCCG. The different colors represent the different ray energies: 100% ≥ red > 66.6%; 66.6% ≥ green > 33.3%; 33.3% ≥ blue > 0.

Fig. 2. Device diagram of the gas Raman spectroscopy system of DNCCG.

Fig. 3. Comparison of Raman spectra of DNCCG (A & B), near-concentric cavities (A, B), and the sum of two near-concentric cavities (A + B).

Fig. 4. Comparison of the Raman signal intensity of DNCCG (A & B), near-concentric cavities (A, B), and the sum of the two near-concentric cavities (A + B).

Fig. 5. Scatterplots for SNR of CO₂ Raman signals in different groups. The incident light power is increased with the group number (Table S2 in Supplementary Material).

Fig. 6. Scatterplots for Δ noise intensity of CO₂ Raman signals in different groups. The incident light power is increased with the group number (Table S2 in Supplementary Material). Δ noise intensity A, B = noise intensity A & B - noise intensity A, B.