Fig. 1. Flowchart of CF-WMS algorithm

Fig. 2. Schematic of experimental device

Fig. 3. Simulated absorption spectra of C2H2 and H2O at 6529.17 cm-1

Fig. 4. Measured background intensity Ibg(t) of N2 gas and laser intensity I(t) after passing into C2H2 gas

Fig. 5. Measured 1f-WMS signal, 2f-WMS signal,2f/1f-WMS signals, together with best fitting and residual signals

Fig. 6. Measured and fitted spectral signal of C2H2 gas with different volume fractions. (a) 10-5; (b) 4×10-5;(c) 1.2×10-4; (d) 4×10-4

Fig. 7. Corresponding relative errors of gas measured concentration and sample concentration

Fig. 8. Allan deviation of system

Fig. 9. Continuous detection results with 2f-WMS and CF-WMS