Observation of Infrared Free-Induction Decay and Optical Nutation Signals from Nitrous Oxide Using a Current Modulated Quantum Cascade Laser

Journal Article · Mon May 07 04:00:00 EDT 2012 · Journal of Chemical Physics

DOI:https://doi.org/10.1063/1.4710540· OSTI ID:1043804

Duxbury, Geoffrey; Kelly, James F; Blake, Thomas A; Langford, Nigel

Free induction decay (FID), optical nutation and rapid passage induced (RP) signals in nitrous oxide, under both optically thin and optically thick conditions, have been observed using a rapid current pulse modulation, or chirp, applied to the slow current ramp of a quantum cascade (QC) laser. The variation in optical depth was achieved by increasing the pressure of nitrous oxide in a long pathlength multipass absorption cell. This allows the variation of optical depth to be achieved over a range of low gas pressures. Since, even at the highest gas pressure used in the cell, the chirp rate of the QC laser is faster than the collisional reorientation time of the molecules, there is minimal collisional damping, allowing a large macroscopic polarization of the molecular dipoles to develop. This is referred to as rapid passage induced gain. The resultant FID signals are enhanced due to the constructive interference between the field within the gas generated by the slow ramp of the laser (pump), and the fast chirp of the laser (probe) signal generated by pulse modulation of the continuously operating QC laser. The FID signals obtained at large 2 optical depth have not been observed previously in the mid-infrared regions, and unusual oscillatory signals have been observed at the highest gas pressures used.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (US)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 1043804
• Report Number(s): PNNL-SA-84720; KP1704020
• Journal Information: Journal of Chemical Physics, Journal Name: Journal of Chemical Physics Journal Issue: 17 Vol. 136; ISSN JCPSA6; ISSN 0021-9606
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
ABSORPTION
DAMPING
DECAY
DIPOLES
INDUCTION
LASERS
MODULATION
NITROUS OXIDE
Non-linear spectroscopy
quantum cascade lasers
free induction decay
adiabatic passage
nitrous oxide
POLARIZATION