Supercontinuum generation with femtosecond dual pumping

We investigate supercontinuum generation with a femtosecond dual-pumping scheme. A 10 MHz oscillator delivering 300 femtosecond pulses at 1028 nm is frequency doubled and both the fundamental and second harmonic are coupled into a micro structured fiber. When the two pulses are temporally overlapped in the fiber a broad supercontinuum appears. By tuning the temporal delay between the two pulses, different regions of the spectrum can be enhanced which allows either improved flatness of the spectrum or selective amplification of regions of interest. The interesting result is shown to arise from cross phase modulation imposed on the visible pulse by fundamental solitons. Results from similar experiments with picosecond and nanosecond dual-wavelength pumping show the same qualitative behaviour and demonstrate that the governing mechanism in all cases is soliton fission and subsequent cross phase modulation of the co-propagating visible pulse.