A system for generating tunable ultrafast optical pulses, comprising a laser source, a gas-filled hollow-core fiber selected for spectrally broadening an input laser pulse by self-phase modulation or Raman effect and a filter unit, wherein an input pulse is spectrally broadened by propagation within said gas-filled hollow-core fiber, and said filter unit selects at least a spectral lobe of a broadened pulse output spectrum, yielding an output pulse shorter than the input pulse and centered at a different frequency.