Nobuyuki Toshima

Coulomb focusing effect on the space distribution of the rescattering electron wavepacket in the laser–atom interaction

We investigated the Coulomb focusing effect on the space distribution of the rescattering electron wavepacket created in the laser–atom interaction solving the time integral equation. The Coulomb focusing is conspicuous in the even-number returns since the rescattering electron energies are lower there. The Coulomb force focuses the rescattering electron beam into a small space and the rescattering electron beam current intensity can reach the order of 1010 A cm−2, much more intense than the conventional electron beam used in scattering experiments. The Coulomb focusing effect plays a less important role for the first return and this explains why the released kinetic energy spectra have a peak at the third return in the experiments of the double ionization of H2 molecules.

Green's function for multielectron ions and its application to radiative recombination involving dielectronic recombinations

We propose a general method to calculate the full Greens function of multielectron atomic ions. The key point exists in the usage of L{sup 2} integrable functions as a complete basis set in a finite region together with an optical potential to guaranty the outgoing scattering boundary condition. In such a way, the cumbersome procedure of adjusting boundary conditions in solving the differential Schroedinger equation is avoided. To show the validity of the method, we studied the radiative recombination involving dielectronic recombinations of Be-like Hg (Z=80) ions. The radiative damping effect is taken into account naturally in the present method. The calculated results reproduce well the asymmetric line profile observed in the experiments.

Two-electron capture with emission of one photon in fast collisions between a highly charged ion and a light atom

We consider the electron capture process in fast non-relativistic ion–atom collisions in which the transfer of two electrons from the atom to the ion is accompanied by emission of one photon with the mean energy ω(2)k about two times larger than that ω(1)k characteristic for the radiative capture of one electron. Such a photon can appear both due to the uncorrelated capture process, in which two electrons are transferred to the ion independently via the non-radiative and radiative capture channels, and due to the correlated two-electron capture, where the electron–electron interaction plays the crucial role. The uncorrelated capture produces a photon spectrum which has a maximum at ω(1)k and gives the main contribution to the two-electron capture. The correlated capture mechanism leads to very small capture cross sections but produces a photon spectrum having a maximum at ~ω(2)k which in principle enables separation of this process in an experiment.

Atomic photoabsorption process controlled by static and oscillating magnetic fields

We present a theoretical method to study atomic photoabsorption processes in a temporally periodic external field. The time development of the atomic dipole moment is propagated by numerical time propagation, and the photoabsorption cross sections is obtained directly from the Fourier transform of the autocorrelation function without summing up over the Floquet-Fourier components. As an example, we study the photoabsorption spectra of hydrogen atoms exposed in a mixture of static and periodically oscillating magnetic fields for the transition from 1s{yields}2p. The atomic energy structure and photoabsorption spectra show interesting dependence on the strength of the oscillating magnetic field. Tuning the combination of the magnetic field strengths, we can control the photoabsorption process. The proposed method is general and can be applied to processes in which the number of relevant high harmonic components of the Fourier expansion is so large that the conventional Floquet method is intractable.

Ionization of hydrogen by ion impact in the presence of a laser field resonant to bound–bound atomic transitions

We study the impact ionization of atomic hydrogen in collisions with fast ions assisted by the pulse of a weak laser field with a sub-nanosecond duration (T ~ 10−10 s). The field is linearly polarized and its frequency is resonant to the 1s–2p hydrogen transitions. We consider the field-assisted impact ionization by using a simple model in which the interaction between the atom and the resonant field is described in the rotating-wave approximation and the interaction of the field-dressed atom with the ion is treated using the continuum-distorted-wave-eikonal-initial-state approach. Our consideration for 1 MeV u−1 C6+–hydrogen collisions shows that the presence of the laser field can have a profound effect on all aspects of the impact ionization, including the angular and energy distributions of the emitted electrons, the total ionization cross section and the projectile scattering.