Optimization of adaptive feedback control for ultrafast semiconductor spectroscopy

We present an experimental study of the control of ultrafast semiconductor nonlinearities by adaptive feedback optical pulse shaping. In the feedback loop, an evolutionary algorithm directs the modulation of the spectral phase of 20-fs laser pulses. In this way, control is achieved over the broadband semiconductor continuum nonlinearity as measured in differential transmission experiments. Design guidelines are given for the implementation of the evolutionary algorithm. Our results demonstrate that a feedback loop with a carefully designed algorithm can serve as a new, sensitive tool in ultrafast semiconductor spectroscopy. Moreover, an optimized feedback loop allows for the substantial enhancement of ultrafast semiconductor nonlinearities. (C) 2001 Optical Society of America.