McManus J B, Kebabian P L, Kolb C E
Appl Opt. 1989 Dec 1;28(23):5016-23. doi: 10.1364/AO.28.005016.
We report the construction of an atmospheric methane measurement instrument based on a Zeeman-split IR He-Ne laser. The laser has a transverse magnetic field over ~2/3 of its gain length and can oscillate at an (unsplit) frequency (2947.91 cm(-1)) centered on a methane absorption line, or on either of two frequencies split by +/-0.055 cm(-1)) from the center, with low CH(4)) absorption. The laser is tuned to dwell sequentially at each frequency, giving two differential absorption measurements in each 46-ms tuning cycle. Atmospheric measurements are made using two multiple pass absorption cells, one with fast (0.75-s) and one with slow (5-s) flow response times. Fluctuations in ambient CH(4)) of ~20-ppb (rms, 1-s averaging) are detected, with interference fringe effects the dominant noise source. The instrument has operated in a field experiment (NASA GTE/ABLE-3A) in Alaska.
我们报告了一种基于塞曼分裂红外氦氖激光器的大气甲烷测量仪器的构建。该激光器在其增益长度的约2/3上具有横向磁场，并且可以在以甲烷吸收线为中心的（未分裂）频率（2947.91 cm⁻¹）上振荡，或者在从中心分裂±0.055 cm⁻¹的两个频率中的任何一个上振荡，同时甲烷吸收较低。激光器被调谐以依次停留在每个频率上，在每个46毫秒的调谐周期内进行两次差分吸收测量。使用两个多程吸收池进行大气测量，一个具有快速（0.75秒），另一个具有缓慢（5秒）的流动响应时间。检测到环境甲烷约20 ppb（均方根，1秒平均）的波动，干涉条纹效应是主要噪声源。该仪器已在阿拉斯加的一次野外实验（NASA GTE/ABLE-3A）中运行。
