Abstract

A compact, sensitive and stable hollow waveguide (HWG) mid-infrared gas sensor, based on gas absorption lines using wavelength modulation spectroscopy with a second harmonic (WMS-2ƒ) detection scheme, was developed for simultaneous measurements of ambient CO₂ and water vapor. Optimization of the laser modulation parameters and pressure parameter in the HWG are performed to improve the strength of the WMS-2f signal and hence the detection limit, where 14.5-time for CO₂ and 8.5-time for water vapor improvement in system detection limit is achieved compared to those working at 1atm. The stability of the sensor has been improved significantly by optimizing environmental disturbances, incoupling alignment of the HWG and laser scanning frequency. An Allan variance analysis shows detection limit of the developed sensor of ∼3 ppmv for CO₂ and 0.018% for water vapor, which correspond to an absorbance of 2.4 × 10⁻⁵ and 2.7 × 10⁻⁵, with a stability time of 160 s, respectively. Ambient CO₂ and water vapor measurement have been performed in two days in winter and spring separately. The measurement precision is further improved by applying a Kalman adaptive filter. The HWG gas sensor demonstrates the ability in environmental monitoring and the potential to be used in other areas, such as industrial production and biomedical diagnosis.

Real-time measurement of CO₂ isotopologue ratios in exhaled breath by a hollow waveguide based mid-infrared gas sensor

Tao Zhou, Tao Wu, Qiang Wu, Chenwen Ye, Rongjing Hu, Weidong Chen, and Xingdao He
Opt. Express 28(8) 10970-10980 (2020)

Compact and portable open-path sensor for simultaneous measurements of atmospheric N₂O and CO using a quantum cascade laser

Lei Tao, Kang Sun, M. Amir Khan, David J. Miller, and Mark A. Zondlo
Opt. Express 20(27) 28106-28118 (2012)

Mid-infrared auto-correction on-chip waveguide gas sensor based on 2f/1f wavelength modulation spectroscopy

Mingquan Pi, Chuantao Zheng, Huan Zhao, Jialin Ji, Zihang Peng, Yuting Min, Yijun Huang, Xueying Wang, Gangyun Guan, Fang Song, Lei Liang, Yu Zhang, Yiding Wang, and Frank K. Tittel
Opt. Lett. 49(2) 190-193 (2024)

CW EC-QCL-based sensor for simultaneous detection of H₂O, HDO, N₂O and CH₄ using multi-pass absorption spectroscopy

Yajun Yu, Nancy P. Sanchez, Robert J. Griffin, and Frank K. Tittel
Opt. Express 24(10) 10391-10401 (2016)

Mid-infrared ChG-on-MgF₂ waveguide gas sensor based on wavelength modulation spectroscopy

Mingquan Pi, Chuantao Zheng, Huan Zhao, Zihang Peng, Jiaming Lang, Jialin Ji, Lei Liang, Yu Zhang, Yiding Wang, and Frank K. Tittel
Opt. Lett. 46(19) 4797-4800 (2021)