Femtosecond pump-probe photoelectron spectroscopy on Na-2: a tool to studybasic coherent control schemes

Femtosecond pump-probe photoelectron spectroscopy has become a common tool in ultrafast gas-phase science because of its sensitivity both to structura l and electronic changes in a molecule upon excitation. Here a summary and extended discussion of our experiments is presented. We focus on the potent ial of this method to study basic femtosecond coherent control schemes. Mul ti-photon excitation of the Na-2 molecule with femtosecond laser pulses lea ds to preparation of vibrational wave packets. Mapping of the vibrational w ave-packet dynamics by time-resolved photoelectron spectroscopy offers the high spatial and temporal resolution required to investigate a variety of l aser-control parameters in great detail. Besides an illustration of the Tan nor-Kosloff-Rice scheme we demonstrate electronic transitions at Franck-Con don forbidden internuclear distances due to the intensity of the applied la ser pulses. Further we discuss the influence of simple phase-modulated (lin early chirped) laser pulses on a molecular multi-photon process. An enhance d population transfer is derived due to synchronization of the wave-packet motion on an electronic potential to an appropriate chirp of the laser puls es. In addition, the influence of the temporal profile on the population tr ansfer and the role of the pulse duration are studied.