Recovery of Absolute Gas Absorption Line Shapes Using Tunable Diode Laser Spectroscopy With Wavelength Modulation-Part I: Theoretical Analysis
Recovery of Absolute Gas Absorption Line Shapes Using Tunable Diode Laser Spectroscopy With Wavelength Modulation-Part I: Theoretical Analysis
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DOI：
10.1109/jlt.2011.2107312
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发表时间：
2011-03-15
影响因子：
4.7
通讯作者：
Duffin, Kevin
中科院分区：
文献类型：
--
作者：
Stewart, George;Johnstone, Walter;Duffin, Kevin
可调谐二极管激光光谱对于各种工业、安全和环境监测应用中的气体检测极其重要。特别令人感兴趣的是开发免校准的独立系统和仪器，这些系统和仪器可以在高温或高压环境（例如燃料电池或燃气涡轮发动机）中运行，在这些环境中可能需要连续和同时监测气体的压力、温度和浓度。在这篇由两部分组成的论文的第 1 部分中，我们介绍了免校准线形恢复的完整理论基础和技术范围，以允许同时测量浓度和压力/温度，以实现广泛的潜在应用。首先，在傅里叶分析的基础上，我们提出了二极管激光器的强度和频率调制产生的一般信号分量，并确定了传统波长调制光谱（WMS）中精确线形恢复相关的问题和困难。然后，我们展示了如何使用一次谐波信号有效地执行线形恢复，并通过使用傅立叶系数的一般校正函数，我们扩展了先前报道的技术，以包括任意大的调制指数、不同的线形轮廓和具有非线性吸收的高气体浓度。先前基于泰勒级数展开的近似技术作为低调制指数傅里叶分析的特例包含在内。我们还表明，通过适当选择调制指数和频率，以这种方式获得的信号幅度可以与传统 WMS 相当，甚至超过。
Tunable diode laser spectroscopy is extremely important for gas detection in a wide variety of industrial, safety and environmental monitoring applications. Of particular interest is the development of calibration-free, stand-alone systems and instrumentation which can operate in high-temperature or high-pressure environments (such as in fuel cells, or gas turbine engines) where continuous and simultaneous monitoring of pressure, temperature and concentration of gases may be required. Here, in Part 1 of this two-part paper, we present the full theoretical basis and range of techniques for calibration-free line-shape recovery to allow simultaneous measurements of concentration and pressure/temperature for a wide range of potential applications. Firstly, on the basis of Fourier analysis, we present the general signal components that arise with both intensity and frequency modulation of diode lasers and identify the issues and difficulties associated with accurate line-shape recovery in conventional wavelength modulation spectroscopy (WMS). We then show how line-shape recovery may be effectively performed using first harmonic signals and, by use of a general correction function from Fourier coefficients, we extend the techniques previously reported to include arbitrary large modulation indices, different line-shape profiles and high gas concentration with non-linear absorption. Previous approximate techniques based on Taylor series expansions are included as a special case of the Fourier analysis for low modulation indices. We also show that the signal amplitudes obtained in this way can be comparable to, or even exceed, that of conventional WMS by appropriate choice of the modulation index and frequency.