Chirped quantum cascade laser induced rapid passage signatures in an optically thick gas

J. H. Northern, G. A. D. Ritchie, E. P. Smakman, J. H. van Helden, R. J. Walker, G. Duxbury

Research output: Contribution to journalArticle

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Abstract

We report observations of rapid passage signals induced in samples of N2O and CH4 present in a multipass cell with an optical path length of 5 m. The effect of laser power and chirp rate upon the signals has been studied by utilising two different chirped quantum cascade lasers operating around 8 mu m. The rapid passage signals exhibit an increasing delay in the switch from absorption to emission as a function of increased gas pressure (up to 8 Torr of gas). By comparing a selection of transitions in N2O and CH4, we show that, unlike ammonia, this `pressure shift' is independent of the transition dipole moment, spectroscopic branch probed and laser chirp rate. As the transition dipole moment is much larger in nitrous oxide than methane, we believe that this indicates that N2O-N2O collisions are more efficient at removing coherence from the polarised sample than CH4-CH4 collisions. We have also observed this pressure shift in a short path length of 40 cm, although with a much reduced value, indicating that propagation effects are important in this optically thick minimally damped system.
LanguageEnglish
Pages37-42
Number of pages6
JournalApplied Physics B: Lasers and Optics
Volume102
Issue number1
DOIs
Publication statusPublished - Jan 2011

Fingerprint

quantum cascade lasers
signatures
chirp
dipole moments
gases
collisions
nitrous oxides
shift
optical paths
gas pressure
lasers
ammonia
methane
switches
propagation
cells

Keywords

  • spectri,
  • signals
  • pulse

Cite this

Northern, J. H., Ritchie, G. A. D., Smakman, E. P., van Helden, J. H., Walker, R. J., & Duxbury, G. (2011). Chirped quantum cascade laser induced rapid passage signatures in an optically thick gas. Applied Physics B: Lasers and Optics, 102(1), 37-42. https://doi.org/10.1007/s00340-010-4159-7
Northern, J. H. ; Ritchie, G. A. D. ; Smakman, E. P. ; van Helden, J. H. ; Walker, R. J. ; Duxbury, G. / Chirped quantum cascade laser induced rapid passage signatures in an optically thick gas. In: Applied Physics B: Lasers and Optics. 2011 ; Vol. 102, No. 1. pp. 37-42.
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Northern, JH, Ritchie, GAD, Smakman, EP, van Helden, JH, Walker, RJ & Duxbury, G 2011, 'Chirped quantum cascade laser induced rapid passage signatures in an optically thick gas' Applied Physics B: Lasers and Optics, vol. 102, no. 1, pp. 37-42. https://doi.org/10.1007/s00340-010-4159-7

Chirped quantum cascade laser induced rapid passage signatures in an optically thick gas. / Northern, J. H.; Ritchie, G. A. D.; Smakman, E. P.; van Helden, J. H.; Walker, R. J.; Duxbury, G.

In: Applied Physics B: Lasers and Optics, Vol. 102, No. 1, 01.2011, p. 37-42.

Research output: Contribution to journalArticle

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