Enhanced excitation and ionization ofH2+by a single- and two-color intense laser pulse

Abstract

We study the enhanced excitation and ionization of $\text{H}_{2}{}^{+}$ by a single- and a two-color intense laser pulse. Our results show that the enhanced ionization in a single-color laser field is closely related to the dominant population of the $1{\ensuremath{\sigma}}_{g}$ or $1{\ensuremath{\sigma}}_{u}$ state and the corresponding width of their Floquet complex quasienergies. The overall trend of the population in higher excited states, once populated, remains flat as a function of time. Therefore, in the single-color case, the excited states do not contribute directly to the ionization. However, when the $\text{H}_{2}{}^{+}$ is exposed to a two-color laser field, an enhanced excitation effect to higher excited states for $\text{H}_{2}{}^{+}$ at some critical internuclear distance ${R}_{c}$ is observed, which contributes greatly to the enhanced ionization of $\text{H}_{2}{}^{+}$ because of their much higher ionization rates compared to those of $1{\ensuremath{\sigma}}_{g}$ or $1{\ensuremath{\sigma}}_{u}$ states. We also find that the enhanced ionization is sensitive to the relative phase of the two-color laser field. By adjusting the relative phase, one can manipulate the enhanced ionization to occur at some critical internuclear distances. This can help the molecule to survive the enhanced ionization peaks at smaller internuclear distances, which is very useful for those circumstances where the preparation of expanded molecules is needed, e.g., for a more efficient generation of high-order harmonic generation. Our method is based on a numerical solution of the full-dimensional time-dependent Schr\"odinger equation accurately using a method we recently developed.