Non-dipole effects in the angular distribution of photoelectrons in sequential two-photon atomic double ionization

Abstract

Abstract. Motivated by the recent achievements of experiments using X-ray free electron lasers, we develop a theory for the angular distributions of photoelectrons in sequential two-photon double ionization (2PDI) of atoms beyond the dipole approximation. Expressions for the angular distributions are obtained taking into account the full multipole expansion of radiation in electric and magnetic moments. The formalism is further specified for the first-order corrections to the dipole approximation. As illustrative example, the sequential 2PDI of the 2p shell in atomic neon is studied. The numerical calculations predict distinct non-dipole effects observable in experiments at present X-ray Free Electron Lasers.

Electron angular distributions of noble gases in sequential two-photon double ionization

“…To confirm our findings and to improve quantitative significance, further measurements at a number of photon energies in the Cooper minimum region are necessary. The role of Cooper minima for sequential ionization processes and its impact on the angular distributions of all involved steps is especially important with respect to a breakdown of the dipole approximation in the non-linear regime [39]. A future investigation of this kind can benefit from the recent prosperity in FEL evolution, especially in terms of wavelength tunabilty.…”

Photoelectron angular distributions and correlations in sequential double and triple atomic ionization by free electron lasers

“…Recent calculations [28,58,59] for the sequential 2PDI in Ne, Ar, and Kr showed that at the photon energies starting from about 1 keV and at lower energies in the region of the Cooper minima, the nondipole corrections could be important for the PADs. General formalism was developed in [59] for the PADs and the angular correlation functions between the emitted electrons for arbitrary polarized photons and taking into account the full multipole expansion of radiation in electric and magnetic moments.…”

“…General formalism was developed in [59] for the PADs and the angular correlation functions between the emitted electrons for arbitrary polarized photons and taking into account the full multipole expansion of radiation in electric and magnetic moments. The development is based, similar as in the dipole approximation, on the stepwise model of the sequential 2PDI and the formalism of statistical tensors.…”

“…The development is based, similar as in the dipole approximation, on the stepwise model of the sequential 2PDI and the formalism of statistical tensors. It was applied to the sequential 2PDI of Ne,Ar, and Kr in [28,58,59]. We refer to original publication [59] for the details of the formalism and here concentrate on some specific features of the angular correlation functions and PAD of the second-step electron related to the nondipole effects.…”

“…Following papers [58,59,62] we restrict ourselves here to the lowest order nondipole corrections that arises due to the interference of the electric dipole (E1) and electric quadrupole (E2) amplitudes. Since the magnetic dipole M1 ionization amplitudes vanish in the nonrelativistic approximation, they were neglected in this study.…”