Effects of Direct Double Auger Decay on the Population Dynamics of Neon Irradiated by Ultraintense x‐ray Pulses

Abstract

The population and charge state distribution of neon interacting with ultraintense x-ray pulses are investigated by solving a time-dependent rate equation in the detailed level-accounting (DLA) approximation. Due to the detailed description of neon atom and ions, our DLA result improves the agreement between predictions and experimental measurements for odd neon charge states. In the framework of the DLA formalism, we further studied the effects of direct double Auger decay (DDAD) on charge state distribution. After the 1s photoionization of neon atom, the DDAD processes give accessible decay channels from the K-shell hole state of Ne + to levels of Ne 3+ , resulting in an increase of the population fraction of Ne 3+ and a decrease of that of Ne 2+ . Compared with the results without considering the DDAD effects, better agreement is obtained between theory and experiment.

Neon in ultrashort and intense x-rays from free electron lasers

“…Our choice of parameters produces a peak intensity of 2.2 × 10 17 W cm 2 which is consistent with 4.5 × 10 17 W cm 2 at a FWHM pulse duration of 140 fs used in Ref. 35 to produce similar theoretical ion yields as the ones shown in the lower panel with the modified rate equations. To achieve about the intensity of Ref.…”

“…Subsequent theoretical research [17,34,35] revealed that there are substantial further many-electron effects in neon in this case. Specifically, shake off following K-shell ionization [17] and double Auger decay of a K-shell vacancy [35] were included in extended rate-equation models for neon. This mitigated substantially the discrepancy found between the ion yields from the experiment and the plain rate equations.…”

“…To gain insights into the time-dependent quantum dynamics of the absorption of x rays and the resulting decay processes, we employ the rate-equation approximation [13,15,16,32,39] that has been used successfully in a number of studies to describe experiments, e.g., Refs. 9,12,13,15,17,31,[33][34][35][36]. Exemplary rate equations for a nitrogen atom restricted to K-shell electrons are given in Ref.…”

“…To achieve about the intensity of Ref. 35 we reduced the FWHM spot size of the x-ray beam. Without reducing the spot size, we would need a factor of 0.635 instead of 0.25 to determine the actual pulse energy from the nominal one; we consider this to be unrealistically high.…”

“…The novel FEL facilities which produce x rays with unprecedented characteristics inspire one to investigate processes, known from the strong-field interaction of optical lasers with atoms, but with x rays that go be-Neon has been studied extensively in LCLS radiation both experimentally [12,17,31] and theoretically [32][33][34][35][36][37]. The quantum dynamics of neon atoms in intense and ultrashort x-ray radiation was initially described theoretically with a plain rate-equation model [12,32,33] that considered only one-photon cross sections and radiative and Auger decay widths.…”