Nonstationary pulse regimes associated with self modulation of a Kerr-lens modelocked Ti:sapphire laser have been studied experimentally and theoretically. Such laser regimes occur at an intracavity group delay dispersion that is smaller or larger than what is required for stable modelocking and exhibit modulation in pulse amplitude and spectra at frequencies of several hundred kHz. Stabilization of such modulations, leading to an increase in the pulse peak power by a factor of ten, were accomplished by weakly modulating the pump laser with the self-modulation frequency. The main experimental observations can be explained with a round trip model of the fs laser taking into account gain saturation, Kerr lensing, and second- and third-order dispersion.
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