Fig. 1. Spectral absorption lines of CO in infrared band

Fig. 2. Spectral absorption lines of CO，CO₂ and H₂O in 1 560~1 575 nm wavelength band

Fig. 3. Schematic of low background noise and differential configuration photoacoustic cell

Fig. 4. Product image of low background noise and differential configuration photoacoustic cell

Fig. 5. Schematic of CO photoacoustic sensor system. Inset：frequency response curve of photoacoustic cell

Fig. 6. Signal to noise ratio of CO photoacoustic sensor as a function of the actual excitation powers

Fig. 7. Signal amplitude of CO photoacoustic sensor as a function of the pressure

Fig. 8. Concentration response linearity of CO photoacoustic sensor