差分法拉第旋转光谱仪在线光减法分析15 NO/14 NO同位素
In-line optical subtraction using a differential Faraday rotation spectrometer for 15NO/14NO isotopic analysis
摘要：
本文介绍了一种用于一氧化氮（NO）同位素体差分测量的双调制法拉第旋转光谱仪。原位样品参考通过差分双池测量完成，在15厘米光路长度内具有3.1 ppbv/rt（Hz）（15 NO）灵敏度。我们的系统工作在1.9倍的散粒噪声限制，与1.8e-7/rt（Hz）的最小分数吸收。示出了14 NO和15 NO两者的差分测量，产生~20 dB的磁光抑制。噪声分析表明，差分信号的稳定性高达~500 s，使用1 ppmv 15 NO（或272 ppmv 14 NO，天然丰度）的归一化比率精度为3.0 permil/rt（Hz）。我们严格模拟我们的差分方法，并证明了实用程序的在线校准精确的同位素比。
英文摘要：
We present a dual-modulation Faraday rotation spectrometer with in-line optical subtraction for differential measurement of nitric oxide (NO) isotopologues. In-situ sample referencing is accomplished via differential dual-cell measurements, with 3.1 ppbv/rt(Hz) (15NO) sensitivity through 15 cm optical path length. Our system operates at 1.9x the shot-noise limit, with a minimum fractional absorption of 1.8e-7/rt(Hz). Differential measurement of both 14NO and 15NO are shown, yielding ~20 dB magneto-optical suppression. Noise analysis demonstrates stability of the differential signal up to ~500 s, with normalized ratiometric precision of 3.0 permil/rt(Hz) using 1 ppmv 15NO (or 272 ppmv 14NO at natural abundance). We rigorously model our differential method and demonstrate the utility of in-line calibration for precise isotopic ratiometry.
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