H2 Double Ionization with Few-Cycle Laser Pulses

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 Schrödinger 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 × 1014 Wcm−2. The proton spectra are shifted to higher energies as the pulse duration is reduced from 40 fs down to 10 fs. The good agreement between the model predictions and the experimental data at 10 fs 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 1 fs 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 4 fs. At 10 fs, the laser intensity dependence of the proton spectra is fairly well reproduced by the model. PACS numbers: 33.80.Rv, 33.80.Eh, 42.50.Vk