Spectral broadening of picosecond laser pulses in optical fibres

Picosecond light pulses of a passively mode-locked ruby laser (pulse duration t _L35 ps) are spectrally broadened in optical fibres of core diameters from 4 m to 600 m. Combining the effects of self-phase modulation, stimulated Raman scattering, and parametric four-photon interaction in an 8-m core fibre of 4 m length with the effect of selective spectral attenuation in a ruby rod resulted in rather smooth spectra extending from 685 nm to 830 nm (spectral width 2300 cm^-1).