Femtosecond pulse shaping using a spatial light modulator and degenerate four-wave-mixing (DFWM) spectroscopy have bee combined to control the vibrational wave packet motion in the electronic ground and excited states of the prototype molecule K_2 and, thus, study the influence of phase and amplitude modulated pulses on the molecular FWM response. It is shown that the vibrational motion of the potassium dimer is sensitive to the temporal interpulse separation and the adjusted phase differences. A simple theoretical model for such arbitrary shaped pulse excitation in a FWM process has been developed, which proves to be in excellent agreement with the observed FWM signal. In addition, the spectrally resolved DFWM signal works as a molecular FROG providing information about the activated molecular vibrations, the DFWM signal itself and the shapes of the pulse used in the excitation sequence. Furthermore, the experiment was ideal to test the robustness of the evolutionary algorithm previously used to find new control processes.
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