Optical re-injection in cavity-enhanced absorption spectroscopy.
Optical re-injection in cavity-enhanced absorption spectroscopy.
复制标题
DOI：
10.1063/1.4893972
复制
发表时间：
2014-09
期刊：
影响因子：
--
通讯作者：
J. Leen;A. O’Keefe
中科院分区：
文献类型：
--
作者：
J. Leen;A. O’Keefe
非模式匹配腔增强吸收光谱（例如腔衰荡光谱和集成腔输出光谱）通常用于痕量气体的超灵敏检测。这些技术因其简单性和鲁棒性而颇具吸引力，但它们的性能可能会受到前镜的光反射以及由此产生的低光透射率的限制。虽然这种低发射功率有时可以通过更高功率的激光器和更低噪声的探测器（例如，在近红外区域）来克服，但在许多情况下，可用的光强度或光电探测器灵敏度限制了仪器性能（例如，在中红外区域）。在本文中，我们描述了一种反复重新注入从光学腔前镜反射的光的方法，以提高腔的循环功率并向光电探测器传送更多的光，从而提高吸收测量的信噪比。我们使用离轴腔衰荡光谱（OA-CRDS）和广泛可调的外腔量子级联激光器来建模并通过实验证明了该方法的性能。通过腔体耦合至检测器的功率增加了 22.5 倍。腔体损耗测量精度为2×10(-10) cm(-1)/√Hz；比标准离轴配置增加了 12 倍，无需重新注入，并且与中红外最佳报告灵敏度相当。最后，重新注入的 CRDS 系统用于测量几种挥发性有机化合物的光谱，证明了解析弱吸收光谱特征的能力得到了提高。
Non-mode-matched cavity-enhanced absorption spectrometry (e.g., cavity ringdown spectroscopy and integrated cavity output spectroscopy) is commonly used for the ultrasensitive detection of trace gases. These techniques are attractive for their simplicity and robustness, but their performance may be limited by the reflection of light from the front mirror and the resulting low optical transmission. Although this low transmitted power can sometimes be overcome with higher power lasers and lower noise detectors (e.g., in the near-infrared), many regimes exist where the available light intensity or photodetector sensitivity limits instrument performance (e.g., in the mid-infrared). In this article, we describe a method of repeatedly re-injecting light reflected off the front mirror of the optical cavity to boost the cavity's circulating power and deliver more light to the photodetector and thus increase the signal-to-noise ratio of the absorption measurement. We model and experimentally demonstrate the method's performance using off-axis cavity ringdown spectroscopy (OA-CRDS) with a broadly tunable external cavity quantum cascade laser. The power coupled through the cavity to the detector is increased by a factor of 22.5. The cavity loss is measured with a precision of 2 × 10(-10) cm(-1)/√Hz; an increase of 12 times over the standard off-axis configuration without reinjection and comparable to the best reported sensitivities in the mid-infrared. Finally, the re-injected CRDS system is used to measure the spectrum of several volatile organic compounds, demonstrating the improved ability to resolve weakly absorbing spectroscopic features.