Delayed rapid passage and transient gain signals generated using a chirped 8 mu m quantum cascade laser

G. Duxbury, N. Langford, K.G. Hay

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Rapid passage signals have been observed in which a delayed switch from absorption to emission is observed as the optical density of acetylene in a long path length cell is increased. The delayed switch results in the generation of a large, narrow, transient gain signal. Using numerical solutions of the Maxwell-Bloch equations we have demonstrated that this effect is due to constructive interference between the incident laser field and the field generated by the response of the gaseous medium. This occurs owing to the minimal collisional damping at the low gas pressures within the gas cell, so that the chirp rate of the laser is faster than the collisional reorientation time of the molecules.
Original languageEnglish
Pages (from-to)3293-3303
Number of pages10
JournalJournal of Modern Optics
Issue number19-20
Publication statusPublished - 2008


  • rapid passage
  • infrared spectroscopy
  • nonlinear optics
  • quantum cascade lasers
  • Maxwell-Bloch equations
  • chirped lasers

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