Fig. 1. Schematic of the flexible hollow core fiber and the transmittance of fiber. (a) Schematic of the flexible hollow core fiber; (b) transmittance

Fig. 2. Schematic of the experimental setup

Fig. 3. Typical injection currents in iCW operation

Fig. 4. Measurement signals of NO and NO₂. (a) Baseline signal (I₀) and transmission signal (I_t); (b) etalon signal; (c) relative wavenumber

Fig. 5. Measured absorption spectra, fitting curves, and fitting residuals of NO and NO₂. (a) NO; (b) NO₂

Fig. 6. Typical S_2f/1f of NO

Fig. 7. S_2f/1fpeak-to-peak amplitude varied with the modulation depth. (a) NO; (b) NO₂

Fig. 8. S_2f/1f at different volume fractions for NO and NO₂, experimental calibration results and fitting curves. (a) S_2f/1fof NO; (b) S_2f/1fof NO₂; (c) experimental calibration results and fitting curve of NO; (d) experimental calibration results and fitting curve of NO₂

Fig. 9. Continuous measurement of 50×10^-6 NO and 15×10^-6 NO₂, the distribution analysis and Allan deviation analysis of the measured volume fraction. Continuous measurement of (a) NO and (b) NO₂; distribution analysis of (c) NO and (d) NO₂; Allan deviation analysis for (e) NO and (f) NO₂