Compact Hollow Waveguide Mid-Infrared Gas Sensor For Simultaneous Measurements of Ambient CO₂ and Water Vapor

Abstract

Rongjing and He, Xing Dao (2020) Compact hollow waveguide mid-infrared gas sensor for simultaneous measurements of ambient CO2 and water vapor.

A Laser-Locked Hollow Waveguide Gas Sensor for Simultaneous Measurements of CO2 Isotopologues with High Accuracy, Precision, and Sensitivity

“…In order to obtain the largest 2f peak values, laser modulation parameters (modulation amplitude and modulation frequency) and pressure in the HWG were all optimized. 14 In order to retrieve unknown concentrations of the three isotopologues 12 CO 2 , 13 CO 2 , and 18 OC 16 O, the relationship between 2f peak values and the three isotopologue concentrations needs to be calibrated. For CO 2 isotopic ratio measurements in human breath, CO 2 concentrations in a range of 2−6% are expected.…”

“…In order to obtain the largest 2 f peak values, laser modulation parameters (modulation amplitude and modulation frequency) and pressure in the HWG were all optimized …”

“…Unfortunately, multimode propagation and scattering on inner reflective coating both may cause optical fringes, which are also sensitive to environmental temperature, current, and mechanical fluctuations, leading to a decrease in the measurement sensitivity. 13,14 In addition, a frequency shift in a free running DFB diode laser due to ambient environmental fluctuations degrades the stability of the laser system. This issue is usually solved by employing a laser frequency locking method.…”

“…An alternative way of increasing the effective absorption path length is to employ hollow waveguide (HWG) fiber or hollow-core fiber (HCF) filled with the gas of interest. ,− Such fiber enables low-loss light propagation in the MIR spectral regions, and its extended optical path (∼m) and small sampling volume (∼mL) guarantee high sensitivity and fast response time for gas concentration measurement. Unfortunately, multimode propagation and scattering on inner reflective coating both may cause optical fringes, which are also sensitive to environmental temperature, current, and mechanical fluctuations, leading to a decrease in the measurement sensitivity. , In addition, a frequency shift in a free running DFB diode laser due to ambient environmental fluctuations degrades the stability of the laser system. This issue is usually solved by employing a laser frequency locking method.…”

Mid-Infrared ZnS Ridge Waveguide Fabricated by Femtosecond Laser Ablation Combined With Ion Irradiation

“…Infrared spectroscopy can simultaneously analyze the content of multiple components in substances, which has the advantages of non-damage, non-pollution, online monitoring and large amount of information on the spectrum. It can be used for the detection of gas, liquid, solid and various complex mixtures [3][4][5]. ZnS crystal is a kind of Ⅱ-Ⅵ semiconductor compound material with a large band gap (3.7 eV) [6][7][8][9].…”