New techniques for determining vibrational temperatures, dissociation, and gain limitations in CW CO₂ lasers

From National Research Council Canada

Alternative title	New techniques for determining vibrational temperatures, dissociation, and gain limitations in CW CO2 lasers
DOI	Resolve DOI: https://doi.org/10.1109/JQE.1980.1070536
Author	Search for: Siemsen, K. J.¹; Search for: Reid, J.; Search for: Dang, C.
Affiliation	National Research Council of Canada
Format	Text, Article
Abstract	We have developed an accurate method of determining vibrational temperatures and populations in CO₂ laser discharges. Our technique involves the use of both the regular 00°1 and sequence 00°2 laser transitions as probes of a CO₂ laser amplifier. We have been able to separately investigate the quantitative effects of gas heating, dissociation, and ν₃ mode excitation efficiency on the small-signal gain in typical CW CO₂ lasers. In general we find that the maximum gain attained in a typical flowing gas CW CO₂ laser is limited by dissociation of CO₂ at high discharge currents. To investigate the more fundamental limitations on the gain, we used a short discharge tube with fast flow rates. Contrary to many previous results, we find that thermal effects play a somewhat secondary role in the discharge dynamics, and that the lower laser level populations are small under all discharge conditions. Our results show that the chief limitation on gain in CW CO₂ lasers is the "saturation" of the ν₃ mode vibrational temperature T₃ at high discharge currents. This saturation effect is observed for a wide range of gas mixtures and pressures, and has been studied in detail. Gain coefficients as high as 3.3 percent/cm have been obtained in a conventional 1-cm bore CW discharge tube. We also report preliminary results of an experiment which uses a tunable diode laser to measure gain on a large variety of transitions in a CO₂ discharge. The diode laser measurements give a striking confirmation of the results described above, and provide the first direct experimental evidence that a Boltzmann distribution exists in the vibrational modes of discharge excited CO₂.
Publication date	1980-06-01
Publisher	IEEE
In	IEEE Journal of Quantum Electronics 16, no. 6: 668–676.
Language	English
Peer reviewed	Yes
NRC number	NRCC 18309 NRC-INMS-2372
NPARC number	8898053
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Record identifier	63404122-290d-452a-9bb7-1027a305e683
Record created	2009-04-22
Record modified	2020-08-21

Date modified:: 2025-11-13