H2 Double Ionization with Few-Cycle Laser Pulses

Abstract

The temporal dynamics of double ionization of H2 has been investigated both experimentally and theoretically with few-cycle laser pulses. The main observables are the proton spectra associated to the H^+ + H^+ fragmentation channel. The model is based on the time-dependent Schr\"odinger equation and treats on the same level the electronic and nuclear coordinates. Therefore it allows to follow the ultrafast nuclear dynamics as a function of the laser pulse duration, carrier-envelope phase offset and peak intensity. We mainly report results in the sequential double ionization regime above 2 10^{14} W/cm^2. The proton spectra are shifted to higher energies as the pulse duration is reduced from 40fs down to 10fs. The good agreement between the model predictions and the experimental data at 10fs permits a theoretical study with pulse durations down to a few femtoseconds. We demonstrate the very fast nuclear dynamics of the H2^+ ion for a pulse duration as short as 1fs between the two ionization events giving respectively H2^+ from H2 and H^+ + H^+ from H2^+. Carrier-envelope phase offset only plays a significant role for pulse durations shorter than 4fs. At 10fs, the laser intensity dependence of the proton spectra is fairly well reproduced by the model.