Abstract
| Language | English |
|---|---|
| Pages | 37-42 |
| Number of pages | 6 |
| Journal | Applied Physics B: Lasers and Optics |
| Volume | 102 |
| Issue number | 1 |
| DOIs | |
| Publication status | Published - Jan 2011 |
Fingerprint
Keywords
- spectri,
- signals
- pulse
Cite this
}
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 journal › Article
TY - JOUR
T1 - Chirped quantum cascade laser induced rapid passage signatures in an optically thick gas
AU - Northern, J. H.
AU - Ritchie, G. A. D.
AU - Smakman, E. P.
AU - van Helden, J. H.
AU - Walker, R. J.
AU - Duxbury, G.
PY - 2011/1
Y1 - 2011/1
N2 - 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.
AB - 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.
KW - spectri,
KW - signals
KW - pulse
UR - http://www.scopus.com/inward/record.url?scp=79851515707&partnerID=8YFLogxK
U2 - 10.1007/s00340-010-4159-7
DO - 10.1007/s00340-010-4159-7
M3 - Article
VL - 102
SP - 37
EP - 42
JO - Applied Physics B: Lasers and Optics
T2 - Applied Physics B: Lasers and Optics
JF - Applied Physics B: Lasers and Optics
SN - 0946-2171
IS - 1
ER -