Intensity dependence of the multielectron dissociative ionization ofN2at 305 and 610 nm

Abstract

We have studied the laser intensity dependence of the multielectron ionization of ${\mathrm{N}}_2$ in the range of ${10}^{13}$–5×${10}^{15}$ W/${\mathrm{cm}}^2$ (laser wavelength 305 and 610 nm; pulse duration 2 ps). At 610 nm, we detect four charge states of atomic fragments (${\mathrm{N}}^{+}$, ${\mathrm{N}}^{2+}$, ${\mathrm{N}}^{3+}$, and ${\mathrm{N}}^{4+}$). The fragment kinetic energies and population intensity dependences indicate that they are produced by a sequential ionization occurring during the dissociation of the molecular ions (from ${\mathrm{N}}_2^{2+}$ to ${\mathrm{N}}_2^{8+}$) and/or formed by subsequent atomic ionization. In the first case our findings imply that the ionization occurs at well-defined internuclear distances. Moreover, the initial kinetic energies of the fragments are independent of the laser intensity. The results are interpreted in terms of laser-pulse development and volume effects. At 305 nm the dissociation processes show a different tendency. We detect two charge states of nitrogen fragments (${\mathrm{N}}^{+}$ and ${\mathrm{N}}^{2+}$) arising from a vertical excitation of the ${\mathrm{N}}_2$ molecules.