Observation of a nearly isotropic, high-energy Coulomb explosion group in the fragmentation ofD2by short laser pulses

We have used momentum spectroscopy to examine the production of deuteron pairs in the double ionization of ${\mathrm{D}}_2$ molecules by a fast $(<\mathrm{}200\mathrm{}\hspace{0.5em}\mathrm{fs}),$ moderately intense $\left[\right(0.65\mathrm{}–8.0)\times {10}^{14}\hspace{0.5em}\mathrm{W}/{\mathrm{cm}}^2]$ laser pulse. By measuring in coincidence the momentum vectors of both deuterons, we have isolated, at the lowest laser power density, a weak ionization channel characterized by Coulomb-explosion deuterons with a sum energy near 10 eV. This is much higher than has been seen in previous studies. The angular distribution of these deuterons is nearly isotropic, in contrast to previous observations that the deuterons are strongly peaked along the laser polarization. These new observations suggest a previously unobserved ionization mechanism.