Group-velocity-matched ultrashort-pulse synthesis in a hollow fibre filledwith a Raman-active gas

Group-velocity mismatch between the pump and probe pulses is shown to limit the minimum duration of ultrashort pulses synthesised through the generati on of multiple Stokes and anti-Stokes sidebands in a Raman-active medium pr eliminary excited by a short laser pulse. The group delay of pulses involve d in short-pulse synthesis in a Raman-active gas can be reduced by using a hollow fibre with a properly chosen inner diameter, gas pressure, and waveg uide modes. The number of Stokes and anti-Stokes sidebands in the nonlinear response of a Raman-active gas can be considerably increased under these c onditions, opening the way to substantially reduce the duration of light pu lses synthesised using this method.