In many experimental setups, stimulated Raman scattering is an attractive method for laser frequency conversion. However, when the conversion must be done in the femtosecond regime, Raman scattering becomes problematic because other nonlinear effects suppress the Raman gain.

By manipulating the polarization of pump and prepump pulses, researchers from Riken in Saitama, Japan, have achieved a laser efficiency of 80 percent for 60-fs-pulse-width Raman sideband radiation produced from H₂ in the spectral range of 360 to 440 nm. As reported in the Feb. 4 issue of Applied Physics Letters, the polarization manipulation allowed the researchers to confine the direction of the pump pulse's energy flow selectively to the anti-Stokes side of the emission without producing any Stokes emissions. They believe the setup is a promising laser source in the sub-100-fs regime.