Phase control of wavepacket dynamics using shaped femtosecond pulses

Coherent vibrational and rotational dynamics of the Li₂ molecule is controlled by varying the relative phases, φ_n, of the rovibrational wavepacket components, | n > e^{-1(ωnt + φn)}. The coherent superposition is created by excitation of a set of ten rovibronic E ¹Σ_g⁺(ν_E = 12-16, J_E = 17, 19) states from an intermediate state, A ¹Σ_u⁺(ν_A = 14, J_A = 18), using ultrashort optical pulses with well defined spectral amplitudes and phases encoded into the pulse by a liquid crystal spatial light modulator. The wavepacket is probed by time-dependent photoionization and the quantum interference signal is measured as a total ionization yield. The phases of the wavepacket components are optimized to produce partial localization of the wavepacket at a given time t, in specific regions of three-dimensional space defined by the radial and angular coordinates. As a result, the ionization yield, I(t), is maximized or minimized at a time t. The degree of control achieved in the experiment (I_max - I_min)/I_max = 64(±12%). The experimental data are interpreted in terms of time-dependent radial and angular probability distributions, calculated for different initial conditions that are determined by the phase relationships in the excitation pulse.