Femtosecond Raman frequency shifter–pulse compressor

The conversion to the first Stokes component at a wavelength of 1.8 μm of ytterbium laser radiation with a pulse duration of 270 fs by stimulated Raman scattering (SRS) in hydrogen was carried out by using double-pulse pumping scheme. Simultaneously with SRS the process of nonlinear phase modulation of laser and Stokes waves was observed. The spectrally broadened chirped Stokes pulse was compressed to 35 fs in fused silica optical elements at the output of a Raman cell.