Energy- and angle-resolved ionization of H2+ interacting with xuv subfemtosecond laser pulses

Abstract

We present an extension of the resolvent operator method to extract fully differential ionization probabilities resulting from the interaction of ultrashort laser pulses with H2+ by including all electronic and vibrational (dissociative) degrees of freedom. The wave function from which ionization probabilities are extracted is obtained by solving the time-dependent Schrödinger equation in a grid for the case of H2+ oriented parallel to the polarization direction of the field. The performance of the method is illustrated by using pulses in the xuv domain. Correlated kinetic-energy (CKE) and correlated angular and nuclear kinetic-energy (CAKN) spectra have been evaluated and used to analyze the underlying mechanisms of the photoionization process. In particular, for pulses with a central frequency ω=0.8 a.u., which is smaller than the vertical ionization potential of H2+, we show the opening of the one-photon ionization channel by decreasing the pulse duration down to less than 1 fs. An analysis of the CKE and CAKN spectra allows us to visualize individual contributions from one- and two-photon ionization processes, as well as to study the variation of these contributions with pulse duration. The latter information is difficult to extract when only the kinetic energy release (KER) spectrum is measured. This points out the importance of performing multiple-coincidence measurements for better elucidation of competing ionization mechanisms, such as those arising when ultrashort pulses are used