1. Atmospheric methane measurement instrument using a Zeeman-split He-Ne laser
- Author
-
J. Barry McManus, Paul L. Kebabian, and Charles E. Kolb
- Subjects
Tunable diode laser absorption spectroscopy ,Zeeman effect ,Absorption spectroscopy ,business.industry ,Materials Science (miscellaneous) ,Atmospheric methane ,Laser ,Industrial and Manufacturing Engineering ,Spectral line ,law.invention ,symbols.namesake ,Optics ,law ,symbols ,Environmental science ,Business and International Management ,Absorption (electromagnetic radiation) ,business ,Noise (radio) - Abstract
The construction of an atmospheric methane measurement instrument based on a Zeeman-split IR He-Ne laser is reported. The laser has a tranverse magnetic field over about 2/3 of its gain length and can oscillate at an (unsplit) frequency (2947.91/cm) centered on a methane absorption line, or on either of two frequencies split by + or - 0.055/cm from the center, with low CH4 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 CH4 of about 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.
- Published
- 2010