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采用外腔量子级联激光器的宽带光谱技术,超越传统吸收测量。

Broadband spectroscopy with external cavity quantum cascade lasers beyond conventional absorption measurements.

作者信息

Lambrecht Armin, Pfeifer Marcel, Konz Werner, Herbst Johannes, Axtmann Felix

机构信息

Fraunhofer Institut für Physikalische Messtechnik, Heidenhofstr. 8, 79110 Freiburg, Germany.

出版信息

Analyst. 2014 May 7;139(9):2070-8. doi: 10.1039/c3an01457f.

Abstract

Laser spectroscopy is a powerful tool for analyzing small molecules, i.e. in the gas phase. In the mid-infrared spectral region quantum cascade lasers (QCLs) have been established as the most frequently used laser radiation source. Spectroscopy of larger molecules in the gas phase, of complex mixtures, and analysis in the liquid phase requires a broader tuning range and is thus still the domain of Fourier transform infrared (FTIR) spectroscopy. However, the development of tunable external cavity (EC) QCLs is starting to change this situation. The main advantage of QCLs is their high spectral emission power that is enhanced by a factor of 10(4) compared with thermal light sources. Obviously, transmission measurements with EC-QCLs in strongly absorbing samples are feasible, which can hardly be measured by FTIR due to detector noise limitations. We show that the high power of EC-QCLs facilitates spectroscopy beyond simple absorption measurements. Starting from QCL experiments with liquid samples, we show results of fiber evanescent field analysis (FEFA) to detect pesticides in drinking water. FEFA is a special case of attenuated total reflection spectroscopy. Furthermore, powerful CW EC-QCLs enable fast vibrational circular dichroism (VCD) spectroscopy of chiral molecules in the liquid phase - a technique which is very time consuming with standard FTIR equipment. We present results obtained for the chiral compound 1,1'-bi-2-naphthol (BINOL). Finally, powerful CW EC-QCLs enable the application of laser photothermal emission spectroscopy (LPTES). We demonstrate this for a narrowband and broadband absorber in the gas phase. All three techniques have great potential for MIR process analytical applications.

摘要

激光光谱学是分析小分子(即气相中的小分子)的有力工具。在中红外光谱区域,量子级联激光器(QCL)已成为最常用的激光辐射源。气相中大分子、复杂混合物的光谱分析以及液相分析需要更宽的调谐范围,因此仍然是傅里叶变换红外(FTIR)光谱学的领域。然而,可调谐外腔(EC)QCL的发展正开始改变这种情况。QCL的主要优点是其高光谱发射功率,与热光源相比提高了10⁴倍。显然,在强吸收样品中使用EC-QCL进行透射测量是可行的,由于探测器噪声限制,FTIR很难进行这种测量。我们表明,EC-QCL的高功率有助于进行超越简单吸收测量的光谱分析。从对液体样品的QCL实验开始,我们展示了用于检测饮用水中农药的光纤倏逝场分析(FEFA)结果。FEFA是衰减全反射光谱学的一种特殊情况。此外,强大的连续波EC-QCL能够对液相中的手性分子进行快速振动圆二色性(VCD)光谱分析——这是一种使用标准FTIR设备非常耗时的技术。我们展示了对手性化合物1,1'-联-2-萘酚(BINOL)获得的结果。最后,强大的连续波EC-QCL能够应用激光光热发射光谱学(LPTES)。我们针对气相中的窄带和宽带吸收体进行了演示。这三种技术在中红外过程分析应用中都具有巨大潜力。

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