Double ionization of He by time-delayed attosecond pulses

Abstract

As He is exposed to double attosecond pulses with a time delay, double ionization can proceed in several different pathways. Through ab initio simulations by the fully dimensional time-dependent Schrödinger equation, we find that interferences among different pathways in the sequential two-photon double ionization can lead to interesting grid-like patterns in the joint energy spectra of the two electrons. We show that not only these interference patterns, but also the total double ionization probability critically depends on the relative carrier–envelope phase (CEP) between the two attosecond pulses. Our findings are successfully explained by a model based on second-order time-dependent perturbation theory. The present study demonstrates the feasibility of CEP control of double ionization, and provides an alternative way to characterize the relative CEP of attosecond pulses.

Multistart spiral electron vortices in ionization by circularly polarized UV pulses

“…In contrast to the present case of single ionization of He, the photon energy ω in each of Refs. [21,22] was always greater than the He binding energy, E b = 24.6 eV. In Ref.…”

“…1(a)] that describe one-photon absorption from each pulse (in the case that the pulses overlap). Clearly, the geometric factor (22) shows that all four pathways lead to the same final state, defined by L = 2 with M L = +2 (M L = −2) for right (left) circularly polarized pulses respectively.…”

“…From the geometric factor (e ·p) 2 (22), where e = e 1 ,e 2 , one sees that the ionization channel 1 ( 2 ) for the first (second) pulse is described by the parameter Using Eqs. (6) and (26) together with the geometric factors (22) and (27), the TDP for a pair of oppositely circularly polarized pulses takes the form…”

“…Two-photon interferometry has recently been used as a tool for investigation of various atomic photoionization processes [21][22][23]. In Refs.…”

“…In Refs. [21,22], double ionization of the helium atom by a pair of time-delayed extreme UV pulses by means of several different pathways was investigated. In contrast to the present case of single ionization of He, the photon energy ω in each of Refs.…”