Adaptive feedback control of ultrafast semiconductor nonlinearities

We experimentally demonstrate that adaptive feedback optical pulse shaping can be used to control ultrafast semiconductor nonlinearities. The control scheme is based on an evolutionary algorithm, which directs the modulation of the spectral phase of 20 fs laser pulses. The algorithm has optimized th e broadband semiconductor continuum nonlinearity measured in differential t ransmission experiments. Our results show that insight into light-semicondu ctor interaction is obtained from the optimum laser pulse shape even if the interaction is too complex to predict this shape a priori. Moreover, we de monstrate that adaptive feedback control can substantially enhance ultrafas t semiconductor nonlinearities by almost a factor 4. (C) 2000 American Inst itute of Physics. [S0003-6951(00)00733-6].