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Title: Pump and probe spectroscopy with continuous wave quantum cascade lasers

This paper details infra-red pump and probe studies on nitric oxide conducted with two continuous wave quantum cascade lasers both operating around 5 μm. The pump laser prepares a velocity selected population in a chosen rotational quantum state of the v = 1 level which is subsequently probed using a second laser tuned to a rotational transition within the v = 2 ← v = 1 hot band. The rapid frequency scan of the probe (with respect to the molecular collision rate) in combination with the velocity selective pumping allows observation of marked rapid passage signatures in the transient absorption profiles from the polarized vibrationally excited sample. These coherent transient signals are influenced by the underlying hyperfine structure of the pump and probe transitions, the sample pressure, and the coherent properties of the lasers. Pulsed pump and probe studies show that the transient absorption signals decay within 1 μs at 50 mTorr total pressure, reflecting both the polarization and population dephasing times of the vibrationally excited sample. The experimental observations are supported by simulation based upon solving the optical Bloch equations for a two level system.
Authors:
; ; ;  [1] ;  [2]
  1. Department of Chemistry, Physical and Theoretical Chemistry Laboratory, The University of Oxford, South Parks Road, Oxford (United Kingdom)
  2. Space Science and Technology Department, STFC Rutherford Appleton Laboratory, Harwell Oxford Campus, Didcot OX11 0QX (United Kingdom)
Publication Date:
OSTI Identifier:
22255146
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Chemical Physics; Journal Volume: 140; Journal Issue: 5; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ABSORPTION; BLOCH EQUATIONS; COLLISIONS; HYPERFINE STRUCTURE; NITRIC OXIDE; POLARIZATION; PROBES; QUANTUM STATES; SIGNALS; SIMULATION; SPECTROSCOPY; TRANSIENTS