Abstract

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 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 ∼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.

© 1989 Optical Society of America

Infrared absorption by methane isotopes near 2999 cm⁻¹: an analytical method using the Zeeman split He–Ne laser line at 2999.24 cm⁻¹

Paul L. Kebabian, Mark S. Zahniser, and Charles E. Kolb
Appl. Opt. 35(12) 1942-1949 (1996)

Stable isotopic analysis of atmospheric methane by infrared spectroscopy by use of diode laser difference-frequency generation

Michael E. Trudeau, Pin Chen, Guilherme de Andrade Garcia, Leo W. Hollberg, and Pieter P. Tans
Appl. Opt. 45(17) 4136-4141 (2006)

Atmospheric extinction measurements of a He–Ne laser

Mario Bertolotti, Mario Carnevale, and Daniele Sette
Appl. Opt. 17(2) 285-288 (1978)

Phase control of a Zeeman-split He–Ne gas laser by variation of the gaseous discharge voltage

W. N. Shelton and R. H. Hunt
Appl. Opt. 31(21) 4154-4157 (1992)

Carbon dioxide absorption of He–Ne laser radiation at 4.2 μm: characteristics of self and nitrogen broadened cases

Craig W. Schneider, Zdenek Kucerovsky, and Eric Brannen
Appl. Opt. 28(5) 959-966 (1989)