Double ionization of helium by electron-impact: complete pictures of the four-body breakup dynamics

The dynamics of He double ionization by 2 keV electron impact is studied experimentally for a momentum transfer of 0.6 a.u. at excess energies of 10 and 40 eV. Complete sets of fivefold differential cross sections are presented for all electron emission angles in coplanar geometry. Contributions beyond the first Born approximation are identified comparing experimental data with first order convergent close-coupling calculations which are in considerably better agreement with the present experiment than with the earlier measurement of Kheifets et al. [J. Phys. B 32, 5047 (1999)]

Appearance and disappearance of the second Born effects in the (e,3e) reaction in He

We demonstrate, both experimentally and theoretically, clear manifestation of the second Born effects in the angular distributions of two ejected electrons produced by a 500 eV electron impact on the He atom in the so-called (e,3e) reaction. The second Born contribution, due to subsequent interaction of the projectile with the target, is most prominent for glancing collisions with small momentum transfer. However, these effects are absent for hard knock-out collisions with large momentum transfer

Projectile-Charge Sign Dependence of Four-Particle Dynamics in Helium Double Ionization

Double ionization of helium by 6 MeV proton impact has been explored in a kinematically complete experiment using a “reaction microscope.” For the first time, fully differential cross sections for positively charged projectiles have been obtained and compared with data from 2 keV electron impact. The significant differences observed in the angular distribution of the ejected electrons are attributed to the charge sign of the projectile, resulting in different dynamics of the four-particle Coulomb system, which is not considered in the first Born approximation

Separation of Recollision Mechanisms in Nonsequential Strong Field Double Ionization of Ar: The Role of Excitation Tunneling

Vector momentum distributions of two electrons created in double ionization of Ar by 25 fs, 0.25PW/cm2 laser pulses at 795 nm have been measured using a “reaction microscope.” At this intensity, where nonsequential ionization dominates, distinct correlation patterns are observed in the two-electron momentum distributions. A kinematical analysis of these spectra within the classical “recollision model” revealed an (e,2e)-like process and excitation with subsequent tunneling of the second electron as two different ionization mechanisms. This allows a qualitative separation of the two mechanisms demonstrating that excitation-tunneling is the dominant contribution to the total double ionization yield

Non-Sequential Double Ionization of Ne in Intense Laser Pulses: A Coincidence Experiment

The dynamics of Neon double ionization by 25 fs, 1.0 PW/cm2 laser pulses at 795 nm has been studied in a many particle coincidence experiment. The momentum vectors of all ejected atomic fragments (electrons and ions) have been measured using combined electron and recoil-ion momentum spectroscopy. Electron emission spectra for double and single ionization will be discussed. In both processes the mean electron energies differ considerably and high energetic electrons with energies of more than 120 eV have been observed for double ionization. The experimental results are in qualitative agreement with the rescattering model

A Subnanosecond Pulsed Ion Source for Micrometer Focused Ion Beams

A new, compact design of an ion source delivers nanosecond pulsed ion beams with low emittance, which can be focused to micrometer size. By using a high-power, 25 fs laser pulse focused into a gas region of 10-6 mbar, ions at very low temperatures are produced in the small laser focal volume of 5 μm diameter by 20 μm length through multiphoton ionization. These ions are created in a cold environment, not in a hot plasma, and, since the ionization process itself does not significantly heat them, have as a result essentially room temperature. The generated ion pulse, up to several thousand ions per pulse, is extracted from the source volume with ion optical elements that have been carefully designed by simulation calculations. Externally triggered, its subnanosecond duration and even smaller time jitter allow it to be superimposed with other pulsed particle or laser beams. It therefore can be combined with any type of collision experiment where the size and the time structure of the projectile beam crucially affect the achievable experimental resolution

Double ionization of helium by electron impact in the impulsive regime

The dynamics of helium double ionization by 2 keV electron impact has been investigated experimentally and theoretically at large momentum transfer of \q\ = 2 a. u. Fully resolved fivefold differential cross sections (FDCS's) are presented for symmetric and asymmetric energy sharing between the two ejected electrons at excess energies from 10 to 40 eV, and for the coplanar as well as the out-of-plane scattering geometries. Experimentally, a multielectron-recoil-ion coincidence technique has been applied and a large part of the final-state momentum space has been mapped. The presently employed theoretical model treats the interaction between the two slow ejected electrons nonperturbatively using the convergent close- coupling method, whereas the projectile-target interaction is described in the first Born approximation. The experimental and theoretical FDCS's agree well in shape. The cross section is dominated by two pairs of strong peaks. From this pattern it can be concluded that the two-step 1 mechanism, which is due to interelectron interaction after a single ionizing collision, is the dominant ionization process for the present kinematics

Puntualizaciones acerca de la aportación diagnóstica y terapéutica de las técnicas angiográficas en la patología tumoral ostearticular

The author reports three cases of aneurysmal bone cysts with angiographic diagnosis with bibliographic review. This method is used for diagnostic usage or preoperatory embolisation method

Double ionization of helium by electron impact in the impulsive regime

The dynamics of helium double ionization by 2 keV electron impact has been investigated experimentally and theoretically at large momentum transfer of \q\ = 2 a. u. Fully resolved fivefold differential cross sections (FDCS's) are presented for symmetric and asymmetric energy sharing between the two ejected electrons at excess energies from 10 to 40 eV, and for the coplanar as well as the out-of-plane scattering geometries. Experimentally, a multielectron-recoil-ion coincidence technique has been applied and a large part of the final-state momentum space has been mapped. The presently employed theoretical model treats the interaction between the two slow ejected electrons nonperturbatively using the convergent close- coupling method, whereas the projectile-target interaction is described in the first Born approximation. The experimental and theoretical FDCS's agree well in shape. The cross section is dominated by two pairs of strong peaks. From this pattern it can be concluded that the two-step 1 mechanism, which is due to interelectron interaction after a single ionizing collision, is the dominant ionization process for the present kinematics