Laser-intensity dependence of the multielectron ionization of CO at 305 and 610 nm

We have studied the multielectron dissociative ionization of CO in the range of ${10}^{13}$–${10}^{15}$ W/${\mathrm{cm}}^2$ (laser wavelength 305 and 610 nm; pulse duration 1.4 and 2 ps, respectively). By measuring the fragment kinetic energies and laser-intensity dependences, we have investigated the detailed dynamics of the interaction process. At 610 nm, the formation of ${\mathrm{CO}}^{3+}$ and ${\mathrm{CO}}^{4+}$ occurs as the molecule dissociates. The transitions occur at well-defined internuclear distances that are shown to be independent of the peak laser intensity. At 305 nm, the ionization processes are found to progress in a different way: CO is multiphoton multiply ionized at the equilibrium internuclear distance of the molecule. This vertical excitation yields fragments with charge states and initial energies lower than at 610 nm. The comparison with the previous results obtained on ${\mathrm{N}}_2$ is discussed.