Nonlinear dynamics inside femtosecond enhancement cavities.

We have investigated the effect of intracavity nonlinear dynamics arising from enhanced peak powers of femtosecond pulses inside broad-bandwidth, dispersion-controlled, high-finesse optical cavities. We find that for chi(3) nonlinearities, when a train of femtosecond pulses are maximally coupled into a cavity by active stabilization of its frequency comb to the corresponding linear resonances of a cavity, enhancement ceases when the peak nonlinear phase shift is sufficient to shift the cavity resonance frequencies by more than a cavity linewidth. In addition, we study and account for the complex spectral dynamics that result from chirping the input pulse and show excellent qualitative agreement with experimental results.