Femtosecond pulse shaping by an evolutionary algorithm with feedback

We report on computer controlled compression of femtosecond laser pulses using a programmable liquid crystal spatial light modulator which is feedback-controlled by an evolutionary algorithm. This algorithm generates the optimal laser field on the basis of feedback from the experiment by optimizing the laser pulse iteratively. Without knowledge of the (chirped) input pulses, the experimental signal (second harmonic light/SHG) is maximized by the algorithm, thus resulting in fully compressed pulses. This method only makes use of the experiment's response (SHG signal) on the formed pulses. No other parameters need to be considered. This approach leads to many experimental applications in all fields of optics and ultrafast spectroscopy where particularly shaped pulses are advantageous.