Transient stimulated Raman scattering in gas mixtures

We studied, for the first time to our knowledge, transient stimulated Raman scattering in H-2-D-2 and H-2-CH4 gas mixtures excited with 200-fs and 2-p s, 390-nm pulses. Depending on the composition and partial pressure, of tho se gases, we observed similar to 40 output lines simultaneously. Under opti mum conditions a conversion efficiency of as much as 8% in the combination Raman line at 556 nm was obtained in the H-2-CH4 gas mixtures. The differen ce between picosecond and femtosecond pumping is due to self-phase modulati on and to generation of a spectral continuum in the latter. Our calculation of the ratio of the partial pressures is in a good agreement with the expe rimental results. A new method for measuring the unknown Raman scattering c ross section of gas molecules is suggested. (C) 1999 Optical Society of Ame rica.