A self-built self-mode-locked Ti:sapphire laser is operated at the upper edge of the stable region. Tow double-prism systems are used to compensate for thesecond-order dispersion in and out of the laser cavity. Broad band laser pulses with bandwidth of 664—840nm have been generated, and their mode changes from the basic mode to the ring structure. The interesting experimental phenomenon is due to the stimulated Raman scattering and the four wave mixing, which provides the necessary condition to generate the sub-10fs laser pulses.