Optical parametric oscillator-based trace detection of gases in the mid-infrared region using phase-fluctuation optical heterodyne spectroscopy
Optical parametric oscillator-based trace detection of gases in the mid-infrared region using phase-fluctuation optical heterodyne spectroscopy
复制标题
使用相涨落光学外差光谱法对中红外区域中的气体进行基于光学参量振荡器的痕量检测
DOI：
10.1117/12.2305736
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发表时间：
2018
期刊：
影响因子：
3.6
通讯作者：
D. Stothard
中科院分区：
文献类型：
--
作者：
Jack W. Thomas;A. Polak;G. Bonner;Sandra Enderle;M. Dunn;D. Stothard
激光吸收光谱法利用可调谐红外光源，提供必要的选择性，以检测丰富气体的特征指纹光谱吸收。在一个简单的实施例中，如单通吸收，灵敏度是有限的，因为衰减成为微量浓度的微小;一个问题加剧了中红外区域由于显着的检测器噪声。可以通过使用多次通过赫里奥特池或谐振腔衰荡光谱法等方法增加光场与分子系综之间的相互作用来提高灵敏度，但这些技术在仪器方面有很大的开销。解决这个问题的另一种方法是相位波动光外差（PFLOH）光谱。在此，当吸收适当波长的入射激光时，使用干涉效应来检测样品气体的微小加热。更具体地，通过将吸收室放置在马赫-曾德尔干涉仪的一个臂内，可以通过所产生的条纹调制以高灵敏度检测光路长度中的热诱导变化。第二个好处是，虽然激发发生在红外线，其效果可以使用可见光激光器和硅探测器检测，从而消除了对冷却的红外探测器的需要。我们将介绍我们的结果用于检测乙烷使用吸收在3.33-3.37 μm的区域。马赫-曾德尔干涉仪使用氦氖激光器作为探测激光器，并使用宽调谐光学参量振荡器（OPO）作为光谱激发。我们已经证明了检测水平在十亿分之几，通过实施几项确定的改进，可以进一步提高灵敏度。
Laser absorption spectroscopy utilizes a tunable infrared source, providing the necessary selectivity, to detect the characteristic fingerprint spectral absorption of an abundant gas. In a simple embodiment such as single-pass absorption, sensitivity is limited as attenuation becomes minuscule for trace level concentrations; a problem exacerbated in the midinfrared region due to significant detector noise. Sensitivity can be improved by increasing interaction between the optical field and molecular ensemble with methods such as a multiple-pass Herriot cell or resonant cavity ring-down spectroscopy but these techniques have a substantial overhead in instrumentation. An alternative approach to this problem is Phase Fluctuation Optical Heterodyne (PFLOH) spectroscopy. Here, interferometric effects are used to detect the minute heating of the sample gas when incident laser light of the appropriate wavelength is absorbed. More specifically, by placing the absorption chamber within one arm of a Mach-Zehnder interferometer, heat-induced changes in the optical path length can be detected with great sensitivity through the resulting fringe modulation. A secondary benefit is that although excitation occurs in the infrared, its effects can be detected using visible lasers and silicon detectors, thereby obviating the need for cooled, infrared detectors. We will present our results used to detect ethane using absorption in the 3.33-3.37 μm region. The Mach-Zehnder interferometer used a Helium Neon laser for the probe laser, and a broadly tunable Optical Parametric Oscillator (OPO) for spectroscopic excitation. We have demonstrated detection levels at parts per billion with further sensitivity possible by implementing several identified improvements.