Feedback optimization of shaped femtosecond laser pulses for controlling the wavepacket dynamics and reactivity of mixed alkaline clusters Original Research Article

In this paper we describe the branching control of different ionization and fragmentation channels of coherently excited Na2K by means of feedback optimization of shaped femtosecond laser pulses. For this purpose the system was first excited with one photon into a pair of intersecting electronic states, from where it was ionized in a two-photonic process, so the resulting ions could size selectively be detected. By employing an evolutionary algorithm for optimizing phase and amplitude of the applied laser field, the relative signal intensities of the resulting mother and fragment ions could significantly be influenced. The peak intensities in the obtained pulse shapes correspond very well to the cross sections of the irradiated transitions; their temporal structure reflects perfectly the wavepacket dynamics of the resulting particles. Hence it was possible to extract with the self-learning algorithm – as postulated by Judson and Rabitz [Phys. Rev. Lett. 68 (1992) 1500] – intrinsic properties from the reactive system in real time.