Optimal coherent Control of the molecular FWM Response by arbitrarily shaped femtosecond Pulses

Coherent control of quantum phenomena can be achieved by using phase- and amplitude modulated laser pulses. With a self-learning loop, which combines a femtosecond pulse shaper, an optimization algorithm and an experimental feedback signal, it is possible to automatically steer the interaction between system and electric field. This approach allows control even without any knowledge of the Hamiltonian. We have successfully implemented this learning loop for the coherent control of the nonresonant two-photon excitation in sodium (3s-5s). New solutions for "bright" and "dark" pulses could be designed for this two-photon resonance without previous knowledge of the resonances. In a further experiment we combined the self-learning loop with degenerate four-wave-mixing spectroscopy (DFWM) in order to study the influence of phase and amplitude modulated pulses on the molecular FWM response of the prototype system K-2. The obtained control pulses typically show a complex structure which hides the responsible physical mechanism. In order to extract the applied mechanism the concept of parameterization has been introduced which allows the learning algorithm to optimize already known control processes. Therefore the control of vibrational wavepacket motion in the electronic ground and excited state could be attributed to chirped pulse excitation, impulsive Raman excitation by pulse trains and phase-related double pulses representing the well-known Tannor-Rice-Kosloff control scheme.