摘要:

An electron injected sideways into the focal region of a tightly‐focused laser beam encounters strong field variations in both space and time. Thus, momentum may be imparted to it by the field in the nature of a small number of violent impulses. Results from single‐particle calculations are presented which demonstrate electron acceleration to GeV energies in petawatt beams focused down to around ten‐micron spot size. We conclude that a captured electron moves effectively in phase with the field and absorbs energy from it.. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1643671

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

A new ultrahigh vacuum‐compatible (∼ 10−11mbar) “reaction microscope” was built to investigate multiple ionization of atoms and molecules in ultra‐short (23 fs), intense laser pulses (1014– 1016W/cm2, 795 nm) . In first experiments ion momentum distributions for single and double ionization of noble gas atoms in the nonsequential and sequential intensity regime were measured using linearly polarized laser pulses. The apparatus is currently improved to perform measurements under even lower residual gas pressures (< 10−13mbar). Furthermore, the new apparatus is ideally suited for future studies on dissociation and Coulomb explosion of molecules. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1643672

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Some of the basic mechanisms governing the physics of the processes occuring when atoms are exposed to intense infrared laser pulses, with peak intensities higher then 1014W/cm2are considered. Special attention is devoted to the actual role of the Coulomb potential in the ejection of electrons of low energy (less than twice the ponderomotive potential). To this end, we study the time evolution of the wavefunction by solving numerically the time‐dependent Schro¨dinger equation for atomic hydrogen inmomentum space. Our results clearly show that it is possible to identify two distinct ionization mechanisms characterized by the emission of “direct” and “indirect” wavepackets in clear contrast with the predictions of the well established strong field approximation. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1643673

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

The combination of B‐spline basis sets with R‐matrix theory has provided a powerful tool for the description of double ionization processes. We demonstrate this first by investigating electron‐impact ionization of Li2+. By applying the Floquet Ansatz, the same techniques can be employed to describe multiphoton double ionization processes through the R‐matrix Floquet approach. Results for two‐photon double ionization of He confirm the lower values of time‐dependent close‐coupling calculations compared to perturbation theory. The approach can be extended to quasi‐two‐electron systems through the use of model potentials. This is demonstrated by calculating photoionization cross sections near threshold for them= 0 level of the 4s4p1Postate of calcium. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1643674

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Convergent close‐coupling (CCC) theory, originally developed to describe electron‐atom collisions, was applied, with a great success, to atomic double photoionization (DPI). DPI from He and its isoelectronic sequence had been studied extensively and prediction of the theory in most cases had been confirmed experimentally. Here we present latest applications of the CCC method to DPI which go beyond simple helium‐like targets. The frozen‐core approximation is used to describe DPI from the valence shell of Be and heavier alkaline‐earth atoms as well as the outermostnp6subshell of noble gases. A “hybrid” model combining a target‐specific ground state and a He‐like final state is employed to describe DPI from subvalent 2s2shell of Ar and the H2molecule. Various shake‐off models are introduced to deal with triple photoionization of Li and Be. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1643675

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

The photoionization of excited He and Xe atoms has been investigated using a combination of a VUV photon (HHG or synchrotron radiation) and a visible laser photon. The well defined degree of polarization of these sources and, in particular, the combined use of linearly and circularly polarized light make it possible to extract detailed information on the symmetry of the excited states as well as on the angular momentum of the outgoing electron. In the case of the Xe* 5p58p’ [K]0,1,2autoionization resonances, excited via the Xe* 5p57s [3/2]1intermediate state, the applied technique leads to the determination of the partial photoionization cross sections related to the continua with total angular momentum J = 0, 1, and 2, respectively. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1643676

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

We have used spin‐resolved electron spectroscopy with circularly polarized synchrotron radiation to delineate the electronic structure of the hydrogen sulfide and carbonyl sulfide molecules and their photoemission dynamics. Specifically, inner‐shell spin‐polarization measurements of the molecular field split components of the S 2p photolines were carried out to reveal effects of the different molecular environments. The validity of simple atomic models to explain the results is discussed. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1643677

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

The theory of angular distributions in atomic and molecular photoionization, formulated in terms of the density matrix and statistical tensor formalism, allows to reveal general features of the nondipole vector correlations in terms of a full multipole expansion of arbitrary polarized radiation in electric and magnetic moments. Some of these features and possible new nondipole effects are discussed. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1643678

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Double ionization of helium in collisions with 6 MeV protons (vP= 15.5 a.u.) has been explored in a kinematically complete experiment using a so‐called “reaction microscope”. For the first time fully differential cross sections for positively charged particle impact have been obtained and compared to previous (e,3e) results with 2 keV electrons (vP= 12 a.u.). Differences have been found in the angular distribution of the two emitted electrons, which originate from projectile charge effects that are not considered in the first Born approximation. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1643679

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

We discuss single and double ionization of atoms by the impact of photons, electrons, and ions. For double ionization, it will be shown that approximations using Coulomb waves for the final state are valid down to much lower energies of the two ejected electrons than previously thought. We also discuss the recent exciting discovery reported inNatureof new effects observed out of the scattering plane for single ionization of helium by heavy‐ion impact. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1643680

出版商:AIP    

年代:1903

数据来源: AIP