We studied, for the first time to our knowledge, transient stimulated Raman scattering in H<sub>2</sub>– D<sub>2</sub> and H<sub>2</sub>– CH<sub>4</sub> gas mixtures excited with 200-fs and 2-ps, 390-nm pulses. Depending on the composition and partial pressure, of those gases, we observed ~40 output lines simultaneously. Under optimum conditions a conversion efficiency of as much as 8% in the combination Raman line at 556 nm was obtained in the H<sub>2</sub>– CH<sub>4</sub> gas mixtures. The difference between picosecond and femtosecond pumping is due to self-phase modulation 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 experimental results. A new method for measuring the unknown Raman scattering cross section of gas molecules is suggested.
© 1999 Optical Society of America
(190.2620) Nonlinear optics : Harmonic generation and mixing
(190.5650) Nonlinear optics : Raman effect
(190.5890) Nonlinear optics : Scattering, stimulated
(190.7110) Nonlinear optics : Ultrafast nonlinear optics
Vitaly Krylov, Ingo Fischer, Victor Bespalov, Dmitry Staselko, and Aleksander Rebane, "Transient stimulated Raman scattering in gas mixtures," Opt. Lett. 24, 1623-1625 (1999)