caa a22 4500 445371676 CHVBK 20180317142949.0 cr unu---uuuuu 170323e20110101xx s 000 0 eng 10.1007/s00340-010-4159-7 doi (NATIONALLICENCE)springer-10.1007/s00340-010-4159-7 Chirped quantum cascade laser induced rapid passage signatures in an optically thick gas [Elektronische Daten] [J. Northern, G. Ritchie, E. Smakman, J. van Helden, R. Walker, G. Duxbury] 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 5m. The effect of laser power and chirp rate upon the signals has been studied by utilising two different chirped quantum cascade lasers operating around 8μm. The rapid passage signals exhibit an increasing delay in the switch from absorption to emission as a function of increased gas pressure (up to 8Torr 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 40cm, although with a much reduced value, indicating that propagation effects are important in this optically thick minimally damped system. Springer-Verlag, 2010 Northern J. Department of Chemistry, Physical and Theoretical Chemistry Laboratory, University of Oxford, South Parks Road, OX1 3QZ, Oxford, UK aut Ritchie G. Department of Chemistry, Physical and Theoretical Chemistry Laboratory, University of Oxford, South Parks Road, OX1 3QZ, Oxford, UK aut Smakman E. Department of Chemistry, Physical and Theoretical Chemistry Laboratory, University of Oxford, South Parks Road, OX1 3QZ, Oxford, UK aut van Helden J. Department of Chemistry, Physical and Theoretical Chemistry Laboratory, University of Oxford, South Parks Road, OX1 3QZ, Oxford, UK aut Walker R. Department of Chemistry, Physical and Theoretical Chemistry Laboratory, University of Oxford, South Parks Road, OX1 3QZ, Oxford, UK aut Duxbury G. SUPA, Department of Physics, University of Strathclyde, John Anderson Building, 107 Rottenrow, G4 0NG, Glasgow, UK aut Applied Physics B Springer-Verlag 102/1(2011-01-01), 37-42 0946-2171 102:1<37 2011 102 340 https://doi.org/10.1007/s00340-010-4159-7 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1007/s00340-010-4159-7 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Northern J. Department of Chemistry, Physical and Theoretical Chemistry Laboratory, University of Oxford, South Parks Road, OX1 3QZ, Oxford, UK aut NATIONALLICENCE 700 1- Ritchie G. Department of Chemistry, Physical and Theoretical Chemistry Laboratory, University of Oxford, South Parks Road, OX1 3QZ, Oxford, UK aut NATIONALLICENCE 700 1- Smakman E. Department of Chemistry, Physical and Theoretical Chemistry Laboratory, University of Oxford, South Parks Road, OX1 3QZ, Oxford, UK aut NATIONALLICENCE 700 1- van Helden J. Department of Chemistry, Physical and Theoretical Chemistry Laboratory, University of Oxford, South Parks Road, OX1 3QZ, Oxford, UK aut NATIONALLICENCE 700 1- Walker R. Department of Chemistry, Physical and Theoretical Chemistry Laboratory, University of Oxford, South Parks Road, OX1 3QZ, Oxford, UK aut NATIONALLICENCE 700 1- Duxbury G. SUPA, Department of Physics, University of Strathclyde, John Anderson Building, 107 Rottenrow, G4 0NG, Glasgow, UK aut NATIONALLICENCE 773 0- Applied Physics B Springer-Verlag 102/1(2011-01-01), 37-42 0946-2171 102:1<37 2011 102 340 Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer