基于柔性空芯光纤的 NO 与 NO₂中红外吸收光谱检测(特邀)

In this study, we report the application of mid-infrared absorption spectroscopy for simultaneous gas sensing of NO and NO₂ using a flexible hollow core fiber (HCF) and two quantum cascade lasers (QCLs). The utilization of QCLs with intermittent continuous wave (iCW) operations and a flexible hollow-core optical fiber can miniaturize sensor systems. The optimal absorption lines for NO and NO₂ detection were selected at approximately 1929. 03 cm⁻¹ and 1599. 91 cm⁻¹, respectively. Both laser beams were simultaneously coupled into a 100 cm flexible HCF with an inner diameter of 530 μm. Initially, direct absorption spectroscopy was performed as an intuitive demonstration of the iCW operation of QCLs with a time-division multiplexing (TDM) strategy for dual-species detection. Following this, we applied wavelength modulation spectroscopy using the first harmonic normalized second harmonic (2f/1f) method to eliminate the influence of any nonabsorption intensity variation, thereby enabling us to thoroughly investigate the performance of the gas sensor. The precision of NO and NO₂ detection was estimated by measuring the concentrations of 50×10⁻⁶ NO and 15×10⁻⁶ NO₂. Results indicated a precision of 5. 2% for NO and 4. 1% for NO₂. Furthermore, we achieved minimum detection limits of 39×10⁻⁹ NO with a 60 s integration time and 9. 2×10⁻⁹ NO₂ with a 50 s integration time.