Cavity-enhanced Faraday rotation spectroscopy for interference-free measurement of OH radical at 2.8 μm

IF 8 1区化学 Q1 CHEMISTRY, ANALYTICAL

Sensors and Actuators B: Chemical Pub Date : 2024-11-05 DOI:10.1016/j.snb.2024.136901

Minh Nhut Ngo , Tong Nguyen-Ba , Nicolas Houzel , Cécile Coeur , Dorothée Dewaele , Fabrice Cazier , Weixiong Zhao , Weidong Chen

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Abstract

An instrument based on cavity-enhanced Faraday rotation spectroscopy (CE-FRS) operating at 2.8 μm has been developed for interference-free measurement of OH radicals in the laboratory. By off-axis coupling of a continuous-wave laser into a high finesse optical cavity, FRS signal is obtained from balanced detection of time-integrated light intensity leaking out of the cavity in the presence of magnetic field. Radio-frequency white noise (5–520 MHz) was injected into laser current which reduced intensity fluctuations in cavity transmission, thus improved the signal-to-noise ratio of the spectroscopic signal by a factor of 2. The setup provides a simple and robust spectroscopic instrument for in-situ and highly-selective detection of paramagnetic species. We demonstrated the instrument’s capabilities using OH radical with concentration in the range of 10¹² molecule.cm⁻³, generated by microwave discharge of water vapor at low pressure. The CE-FRS instrument exhibited a limit of detection of ∼ 10¹⁰ molecule.cm⁻³ in an integration time of 20 s, which is enhanced by a factor of 2.5 compared to cavity-enhanced wavelength modulation spectroscopy involving an off-axis integrated cavity output spectroscopy approach. A time-resolved FRS signal was recorded in a pulsed microwave discharge regime, giving a millisecond time resolution for the measurement of OH concentration profile. The developed instrument provides a potential analytical tool for the measurement of OH concentration for chemical kinetic study in reactor cells.

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用于在 2.8 μm 波长下无干扰测量 OH 自由基的空穴增强法拉第旋转光谱法

我们开发了一种基于空腔增强法拉第旋转光谱（CE-FRS）的仪器，其工作波长为 2.8 μm，用于在实验室中对 OH 自由基进行无干扰测量。通过将连续波激光器离轴耦合到高精细度光腔中，在磁场存在的情况下，法拉第旋转光谱信号可通过平衡检测从腔中漏出的时间积分光强获得。在激光电流中注入射频白噪声（5-520 MHz），可减少腔体传输中的强度波动，从而将光谱信号的信噪比提高 2 倍。该装置为原位和高选择性检测顺磁物种提供了一个简单而强大的光谱仪器。我们使用低压水蒸气微波放电产生的浓度在 1012 摩尔.厘米-3 范围内的 OH 自由基演示了该仪器的功能。在 20 秒的积分时间内，CE-FRS 仪器的检测限为 ∼ 1010 molecule.cm-3，与采用离轴集成腔输出光谱方法的腔增强波长调制光谱相比，提高了 2.5 倍。在脉冲微波放电条件下记录了时间分辨 FRS 信号，测量 OH 浓度曲线的时间分辨率为毫秒级。所开发的仪器为测量反应器电池中化学动力学研究的 OH 浓度提供了一种潜在的分析工具。

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来源期刊

Sensors and Actuators B: Chemical 工程技术-电化学

CiteScore

14.60

自引率

11.90%

发文量

1776

审稿时长

3.2 months

期刊介绍： Sensors & Actuators, B: Chemical is an international journal focused on the research and development of chemical transducers. It covers chemical sensors and biosensors, chemical actuators, and analytical microsystems. The journal is interdisciplinary, aiming to publish original works showcasing substantial advancements beyond the current state of the art in these fields, with practical applicability to solving meaningful analytical problems. Review articles are accepted by invitation from an Editor of the journal.