Electron Wavepacket Phases in Ionization and Rescattering Processes by Intense Laser Pulses

Exact numerical solutions of the time-dependent Schrodinger equation, TDSE, are presented for the H atom and H(2)(+) molecular ion ionized by short (10 optical cycles), intense I(0) >= 10(14) W/cm(2), 800 nm laser pulses. Calculations of the time dependent expectation values of the dipole moment d(t), velocity (d)over dot(t), and acceleration (d)over dots(t) are used to identify the phase of these physical parameters with respect to the laser field during the harmonic generation process. It is found in general that electron wavepackets in an inner region near the parent ion are out of phase with the response expected from the classical laser induced recollision model, whereas wavepackets in an outer region, far from the parent ion, are in phase with the field force. It is found furthermore that it is the inner electron wavepacket which contributes mainly to the high order harmonic generation, HHG, process, even though its acceleration is out of phase with the field force. This suggests strong Coulomb refocussing effects in the HHG process, especially in the case of H(2)(+).