Electronics Technology Department, Universidad Carlos III de Madrid , C/Butarque 15, 28911 Leganés, Madrid, Spain.
Institute of Chemical Technologies and Analytics, Technische Universität Wien , Getreidemarkt 9/164-UPA, 1060 Vienna, Austria.
Anal Chem. 2017 Jun 6;89(11):5916-5922. doi: 10.1021/acs.analchem.7b00303. Epub 2017 May 15.
Molecular dispersion spectroscopy encompasses a group of spectroscopic techniques for gas analysis that retrieve the characteristics of the sample from the measurement of the profile of its refractive index in the vicinity of molecular resonances. This approach, which is in clear contrast to traditional methods based on the detection of absorption, provides inherent immunity to power fluctuations, calibration-free operation, and an output that is linearly dependent on gas concentration. Heterodyne phase-sensitive dispersion spectroscopy (HPSDS) is a very recently proposed technique for molecular dispersion spectroscopy based on tunable lasers that is characterized by a very simple architecture in which data processing and concentration retrieval are straightforward. Different HPSDS implementations have been experimentally validated in the near-IR. Here, we present the first demonstration of HPSDS in the mid-IR using a directly modulated quantum cascade laser for the measurement of CO. The setup is put under test to characterize its response to changing concentrations, pressures, and levels of optical intensity on the detector, and the limit of detection is estimated. Besides this, an experimental comparison with wavelength modulation spectroscopy with second-harmonic detection (2f-WMS) is performed and discussed in detail in order to offer a clear view of the benefits and drawbacks that HPSDS can provide over what we could consider the reference method for gas analysis based on tunable laser spectroscopy.
分子分散光谱学包括一组用于气体分析的光谱技术，这些技术通过测量分子共振附近样品折射率的分布来获取样品的特性。与基于吸收检测的传统方法相比，这种方法具有固有抗功率波动、免校准操作以及与气体浓度呈线性相关的输出等优点。外差相敏分散光谱学（HPSDS）是一种非常新的基于可调谐激光器的分子分散光谱学技术，其特点是具有非常简单的架构，其中数据处理和浓度提取非常简单。不同的 HPSDS 实现已经在近红外区域得到了实验验证。在这里，我们首次在中红外区域使用直接调制的量子级联激光器演示了 HPSDS，用于测量 CO。该设置经过测试，以表征其对浓度、压力和探测器上的光强变化的响应，并估计检测限。除此之外，还进行了与二次谐波检测的波长调制光谱学（2f-WMS）的实验比较，并进行了详细讨论，以便清楚地了解 HPSDS 相对于我们认为基于可调谐激光光谱学的气体分析参考方法的优缺点。
