Designing laser pulses for the coherent control of state-selected wave packet excitation in lithium dimer

Phase and amplitude shaping of ultrafast laser pulses is used to control the coherent excitation and evolution of rotational and vibrational superpositions in lithium dimer. A narrow band laser excites a single transition from the electronic ground state to a ro-vibrational level of the A 1 S+u electronic state. A liquid crystal spatial light modulator is used to shape 800 nm pulses for wave packet excitation. A phase and amplitude shaped broadband laser pulse excites a superposition of ro-vibrational levels of both the A 1 S+u state and the E 1 S+g state by ionization. A second ultrafast laser pulse probes the evolution of the superposition state.;Frequency chirped pump laser pulses are shown to enhance coherences between specific levels excited by stimulated, resonant Raman transitions. The sign of the chirp rate, either positive or negative, controls whether the lower or upper Raman transition is excited. Time-dependent perturbation theory calculations demonstrate that the transitions are excited sequentially and that population transfer to the Raman excited level is increased when the frequencies within the laser pulse are arranged in the correct sequence.;A sequence of pulses that excite different vibrational levels of the E 1 S+g state but the same Raman levels on the A 1 S+u state is shown to be an effective method by which to control the amplitude of a single level within a complex superposition. The time delay between the two excitation pulses and the relative phases of resonant transition frequencies are both shown to effectively control the intensity of the quantum beats excited by Raman transitions, which are indicative of the individual state amplitudes, while leaving the rest of the superposition unaltered.;Finally, pulse shaping techniques for 400 nm light by sum frequency generation are investigated and preliminary results from the velocity map imaging setup for coherent control of polyatomic molecules are presented.