Ultrabroad bandwidth stimulated Raman scattering by femtosecond pulse excitation of gases in a hollow waveguide

Summary form only given. Spectral continuum generation by ultrashort pulses propagating in a hollow waveguide, in combination with compression by compensation of group velocity dispersion provides means for obtaining sub 10-fs optical pulses. Because of large dispersion of optical materials at UV and blue-green wavelengths, it has been difficult so far to obtain energetic sub-10 fs pulses in the short wavelength range. We have shown recently that stimulated Raman scattering (SRS) of 390 nm wavelength ultrashort pulses in gases such as H/sub 2/, D/sub 2/, HD and CH/sub 4/, is accompanied by generation of a broad spectral background, which spans several vibrational and rotational Stokes lines as well as the broadened Rayleigh line. It was indicated that this effect can be used to produce short wavelength pulses comprising only a few oscillation periods of optical field. In the paper we demonstrate that by using hollow waveguide in the SRS cell we can greatly enhance the spatial coherence of the SRS pulses, which is necessary for efficient pulse compression. We show that the increased efficiency of the SRS process in the waveguide configuration allows generation of ultra broad spectrum with width up to 10 000 cm/sup -1/. Furthermore, we apply computer simulations based on direct electromagnetic pulse propagation to model the process of broad spectrum generation in Raman active media.