Excitation of laser-induced thermal gratings in the gas phase via Raman-active transitions

A systematic account of the properties of a recently developed coherent Ram an technique is given. This is a time-resolved technique, based on the gene ration of thermal gratings due to a population change induced by stimulated Raman pumping of molecular levels. Excitation of gratings is achieved by s patially and temporally overlapping intensity interference patterns indepen dently generated by two lasers with appropriate wavelengths. By employing t his technique, it is possible to investigate gas transport properties and m olecular energy relaxation processes, as has been shown for carbon dioxide. The transitions of the Q-branches of the v(1)/2v(2) Fermi dyad were used f or Raman pumping in neat gas and in mixtures with argon, A possibility to p erform spectroscopy of Raman-active transitions has also been demonstrated. (C) 1999 Published by Elsevier Science B.V. All rights reserved.