Effects of single-photon double photoionization and direct double Auger decay on K-shell ionization kinetics of Ar atoms interacting with XFEL pulses

Abstract

In studies investigating the interaction of matter with ultraintense, ultrashort Xray free electron laser (XFEL) pulses, the evolution kinetics are generally described by directly solving a time-dependent rate equation that considers single-photon and single-electron processes. In the present study, we show the effects of single-photon double photionization and direct double Auger decay in the K-shell ionization kinetics of XFELs interaction with argon atoms. Because a huge number of coupled transition channels are present in the K-shell ionization, we develop a Monte Carlo method to simulate the complex ionization kinetic processes and give the level population evolution of ions and charge state distribution (CSD). The K-shelldominated ionization dynamics of Ar irradiated by XFEL pulses with photon energies of 5000, 5500 and 6500 eV are investigated and compared with available experimental observations of the CSD. The results show that the population fractions of Ar5+, Ar6+ and Ar9+ are increased by 78%, 152% and 144%, respectively, by these higher-order processes at a photon energy of 5000 eV. Including the direct double-electron processes, the predicted CSDs are in better agreement with the experiments carried out at the photon energies of 5000, 5500 and 6500 eV. It is expected that the developed theoretical formalism can be used to more accurately calibrate the beam profile and intensity of XFELs.

Coupled Electron–Nuclear Dynamics Induced and Monitored with Femtosecond Soft X-ray Pulses in the Amino Acid Glycine

“…The cross-section of this high-order process can be up to 4 orders of magnitude lower than that of direct photoionization, , which depends on the photon energy and the involved electron binding energies. The amount of energy shared and thus the splitting ratio of the electrons’ kinetic energies is a complex quantum many-body problem and relates to the question whether the secondary electron is ejected through a shakeup or knockout mechanism, which is still subject of active research, but not in the focus of the present study. We note in passing that the coincidence peak of Auger electrons between 170 and 207 eV and corresponding photoelectrons at 29 eV (horizontal ellipse in Figure ) originates from residual argon gas, which was used for spectrometer calibration prior to the glycine measurements. Likewise, the coincidence events at around 163 eV and <80 eV (vertical ellipse) are a result of double Auger decay in argon .…”

“…Their kinetic energies can be at most 241 eV, due to the molecules’ double-ionization potential of 32 eV and the FEL photon energy of 273 eV. The cross-section of this high-order process can be up to 4 orders of magnitude lower than that of direct photoionization, 11 , 12 which depends on the photon energy and the involved electron binding energies. The amount of energy shared and thus the splitting ratio of the electrons’ kinetic energies is a complex quantum many-body problem and relates to the question whether the secondary electron is ejected through a shakeup or knockout mechanism, which is still subject of active research, 11 but not in the focus of the present study.…”

Theoretical study of the enhancement of saturable absorption of Kr under x-ray free-electron laser

“…In the study of the interactions between free electron lasers and atoms, the HFS model has been widely used and proven to be efficient. [19][20][21]…”

“…In the actual experiment of free-electron laser, the distribution of light intensity follows not only the Gaussian distribution of time, but also the Gaussian distribution of position and photon frequency. We assume that the beam is a circular spot, and the general formula of light intensity satisfies the Gaussian distribution of space, time, and photon frequency, [19][20][21] I ν (r,t) = I 0 e − ln 2a( r 1 ∆ )…”

“…[27] When compared with the experimental values, there were some differences between the Kr 1+ , Kr 2+ , and Kr 4+ . The differences are possibly due to the relatively few physical processes considered, such as single photon multi-ionization, double Auger decay, and resonant excitation to the parameter fitting, [20,28,29] which can provide better agreement to the experimental results. [26] and another theoretical result.…”