Ionization and dissociation of H2 with intense and ultra-short laser pulses at 780 nm and 390 nm

We have studied the ionization and dissociation of H2 molecules, exposed to intense short-pulse radiation at 780 nm and its second harmonic at 390 nm. We report the observation of a substantial enhancement in H2+ and H+ ion production when the two colours are superposed. We have measured the ionization yield under similar experimental conditions for comparison. A strong dependence of ion yield on the relative directions of the polarization of the two fields is also observed. In order to gain more insight into the dynamics, H+ kinetic-energy spectra have been measured at different laser intensities for both wavelengths, both separately and with them superposed. For 390 nm radiation, these are the first H+ kinetic-energy spectra reported for intense sub-picosecond induced dissociation. The experimental results are discussed and compared with the existing theoretical calculations. (author)