When an intense laser pulse ionizes a molecule, many electrons can be removed. If their number is sufficiently high, the molecular system fragments and there is repulsion between each ion. If the charge (Z) is sufficiently high, the potential can be approximated by a Coulombic potential. The measurement of the three-dimensional velocities allows us to reconstruct the molecular structure before the Explosion. The structure is calculated by assuming classical trajectories on Coulomb potential.
The quality of imaging depends on the time it takes to change the charge state from 0 to Z. This time is determined by the duration of the laser pulses. Sub-10 fs laser pulses are now available. First, with such pulses, we show that the ionization of D2 takes less then 5 fs [1]. We show that we have enough resolution with such pulse to investigate the molecular dynamics that follow single ionization of D2.
For diatomic molecules, the total kinetic energy of the fragments is directly linked to the molecular structure. For triatomic, we need the full momentum distribution. We show how this is done experimentally and we show results for imaging triatomic molecules. Finally, we will show that this technique can be used in pump-probe experiments that follow photodissociation of triatomic molecules.
[1] Légaré et al, Physical Review Letters 91, 093002 (2003).Contact Wendell Hill III.