Group-delay-free synthesis of ultrashort pulses in a hollow fiber with a Raman-active gas

Group-delay effects are shown to limit the minimum duration of short pulses synthesized through the generation of multiple Stokes and anti-Stokes side bands in an impulsively pre-excited Raman-active medium. The group delay of pulses involved in short-pulse synthesis in a Raman-active gas can be redu ced by using a hollow fiber with a properly chosen gas pressure, inner diam eter, and waveguide modes. The number of Stokes and anti-Stokes sidebands i n the nonlinear response of a Raman-active gas can be considerably increase d under these conditions, opening the way to substantially reduce the durat ion of light pulses synthesized with the use of this method.