Durry G, Pouchet I, Amarouche N, Danguy T, Megie G
Institut Pierre-Simon-Laplace, Service d'Aéronomie, Centre National de la Recherche Scientifique, B.P. 3, 91371 Verrières-le-Buisson Cédex, France.
Appl Opt. 2000 Oct 20;39(30):5609-19. doi: 10.1364/ao.39.005609.
A dual-beam detector is used to measure atmospheric trace species by differential absorption spectroscopy with commercial near-infrared InGaAs laser diodes. It is implemented on the Spectromètre à Diodes Laser Accordables, a balloonborne tunable diode laser spectrometer devoted to the in situ monitoring of CH4 and H2O. The dual-beam detector is made of simple analogical subtractor circuits combined with InGaAs photodiodes. The detection strategy consists in taking the balanced analogical difference between the reference and the sample signals detected at the input and the output of an open optical multipass cell to apply the full dynamic range of the measurements (16 digits) to the weak molecular absorption information. The obtained sensitivity approaches the shot-noise limit. With a 56-m optical cell, the detection limit obtained when the spectra is recorded within 8 ms is approximately 10(-4) (expressed in absorbance units). The design and performances of both a simple subtractor and an upgraded feedback subtractor circuit are discussed with regard to atmospheric in situ CH4 absorption spectra measured in the 1.653-microm region. Mixing ratios are obtained from the absorption spectra by application of a nonlinear least-squares fit to the full molecular line shape in conjunction with in situ P and T measurements.
一种双光束探测器用于通过差分吸收光谱法，利用商用近红外铟镓砷激光二极管测量大气痕量物种。它安装在可调节二极管激光光谱仪上，这是一种用于原位监测甲烷和水的气球载可调谐二极管激光光谱仪。双光束探测器由简单的模拟减法器电路与铟镓砷光电二极管组成。检测策略是在开放光学多程池的输入和输出处检测到的参考信号和样品信号之间取平衡的模拟差值，以便将测量的全动态范围（16位）应用于微弱的分子吸收信息。所获得的灵敏度接近散粒噪声极限。使用56米的光学池，在8毫秒内记录光谱时获得的检测限约为10^(-4)（以吸光度单位表示）。针对在1.653微米区域测量的大气原位甲烷吸收光谱，讨论了简单减法器和升级后的反馈减法器电路的设计与性能。通过对全分子线形应用非线性最小二乘法拟合并结合原位压力和温度测量，从吸收光谱中获得混合比。
