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

摘要

A systematic account of the properties of a recently developed coherent Raman technique is given. This is a time-resolved technique, based on the generation of thermal gratings due to a population change induced by stimulated Raman pumping of molecular levels. Excitation of gratings is achieved by spatially and temporally overlapping intensity interference patterns independently generated by two lasers with appropriate wavelengths. By employing this technique, it is possible to investigate gas transport properties and molecular energy relaxation processes, as has been shown for carbon dioxide. The transitions of the Q-branches of the ν_1/2ν_2 Fermi dyad were used for Raman pumping in neat gas and in mixtures with argon. A possibility to perform spectroscopy of Raman-active transitions has also been demonstrated.