Cryogen-free heterodyne-enhanced mid-infrared Faraday rotation spectrometer.
Cryogen-free heterodyne-enhanced mid-infrared Faraday rotation spectrometer.
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DOI：
10.1364/oe.21.000740
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发表时间：
2013-01
期刊：
影响因子：
3.8
通讯作者：
Yin Wang;M. Nikodem;G. Wysocki
中科院分区：
文献类型：
--
作者：
Yin Wang;M. Nikodem;G. Wysocki
提出了一种新的顺磁分子物种法拉第旋转谱的检测方法。利用外差增强型法拉第旋转谱(H-FRS)系统，在没有任何低温制冷的情况下，展示了在中红外波段的近散粒噪声限制性能。从理论上分析了外差式和常规式FRS对偏振旋转的极限灵敏度。用基于热电致冷5.24μm量子级联激光器和汞镉碲光电探测器的氢荧光光谱系统实现了对一氧化氮(NO)的传感。通过在射频范围内进行外差检测，在很大程度上避免了低频时占主导地位的QCL相对强度噪声。H-FRS的总噪声水平仅为基本散粒噪声的3.7倍。该系统对偏振旋转的灵敏度为1.8×10(-8)rad/Hz(1/2)，仅比理论估计的极限灵敏度高5.6倍。利用NO在1906.73 cm(-1)处的R(17/2)跃迁，获得了3.1ppbv-m/Hz(1/2)的路径和带宽归一化的NO检测下限。
A new detection method for Faraday rotation spectra of paramagnetic molecular species is presented. Near shot-noise limited performance in the mid-infrared is demonstrated using a heterodyne enhanced Faraday rotation spectroscopy (H-FRS) system without any cryogenic cooling. Theoretical analysis is performed to estimate the ultimate sensitivity to polarization rotation for both heterodyne and conventional FRS. Sensing of nitric oxide (NO) has been performed with an H-FRS system based on thermoelectrically cooled 5.24 μm quantum cascade laser (QCL) and a mercury-cadmium-telluride photodetector. The QCL relative intensity noise that dominates at low frequencies is largely avoided by performing the heterodyne detection in radio frequency range. H-FRS exhibits a total noise level of only 3.7 times the fundamental shot noise. The achieved sensitivity to polarization rotation of 1.8 × 10(-8) rad/Hz(1/2) is only 5.6 times higher than the ultimate theoretical sensitivity limit estimated for this system. The path- and bandwidth-normalized NO detection limit of 3.1 ppbv-m/Hz(1/2) was achieved using the R(17/2) transition of NO at 1906.73 cm(-1).