Generation of high-order rotational lines in hydrogen by four-waveRaman mixing in the femtosecond regime

摘要

More than 40 rotational Raman lines are generated using an 800-fsnTi:sapphire laser. The spectral region extends from the near-infrared tonthe far-ultraviolet with a considerably flat intensity distribution. Theneffects of laser polarization, pulsewidth, hydrogen pressure, andnfocusing conditions on the efficiencies of stimulated Raman scattering,nfour-wave Raman mixing, self-phase modulation, self-focusing, andnharmonic generation are investigated. A white light continuum, generatednby self-phase modulation, acts as a seed beam for the generation ofnhigh-order rotational lines through four-wave Raman mixing. Strongnself-phase modulation, however, suppresses the generation of the Ramannemission, due to a line broadening of the pump beam. Thus, optimizationnof experimental conditions is necessary for the efficient generation ofnhigh-order rotational lines