The authors have studied the multielectron dissociative ionization of CO using a linearly polarized YAG laser delivering 10 W cm at 1064 nm, with a pulse duration of 30 ps. By firing two identical laser pulses, with crossed polarizations and a time delay of 800 ps, they show that an intense laser field forces all the molecules to align along its polarization vector. The molecular confinement increases with the dissociation threshold energies of the decay paths involved. Surprisingly enough, the different molecular decay paths observed with a 30 ps pulse release the same 'magic' kinetic energies as already observed with 100 fs, 600 fs and 2 ps pulse durations.

H2 molecules were ionized by Ti:sapphire (45 fs, 800 nm) and Nd-doped yttrium aluminum garnet lasers (6 ns, 1064 nm). The relative populations of the vibrational levels of the H+2 ions were determined and found to be concentrated in the lowest vibrational levels. Tunneling ionization calculations with exact field-modified potential curves reproduce the experimental results. The reason for the departure from conventional Franck-Condon-like distributions is the rapid variation of the ionization rate with internuclear distance.

Nonsequential double ionization of several molecules such as N 2 ,CO 2 ,C 2 H 2 , and C 3 H 4 in strong laser fields has been unambiguously identified from the ion-yield measurements in comparison with a sequential ionization model in the 10 13 -10 15 W/cm 2 laser intensity range. This effect is observed mainly using linearly polarized laser light. In circular polarization, nonsequential double ionization might be present, for instance for the C 2 H 2 molecule, but with a much lower contribution than in linear polarization. The experimental method allows us to detect all the double-ionization decay channels that are the molecular dication and the two-missing electron fragmentation channels. The validity of a single-ionization tunneling model developed for atoms has been extended to molecules, and a good agreement is observed in laser intensity ranges where single-ionization processes take place.

No abstract

No abstract

No abstract

The Coulomb explosion of CO2 into multicharged atomic ions is investigated following the ejection of up to 9 electrons by an intense femtosecond laser field. The identification of several fragmentation channels OZ++CZ'++OZ"+ is performed from triple ion correlation experiments. As already observed for the Coulomb explosion of N2 by a strong picosecond laser field. the measured kinetic energy releases are 50% weaker than the Coulomb repulsion energies calculated at the equilibrium internuclear distances. In addition, there is evidence for bending of the molecule during the explosion around the average linear structure. This experimental observation is tentatively assigned to bending vibrations arising from the violent laser-induced alignment of the molecule along the laser polarization direction before the explosion.

No abstract