165 research outputs found
Photodetachment of H near a partial reflecting surface
Theoretical and interpretative study on the subject of photodetachment of
H near a partial reflecting surface is presented, and the absorption
effect of the surface is investigated on the total and differential cross
sections using a theoretical imaging method. To understand the absorption
effect, a reflection parameter is introduced as a multiplicative factor to
the outgoing detached-electron wave of H propagating toward the wall. The
reflection parameter measures, how much electron wave would reflect from the
surface; K=0 corresponds to no reflection and K=1 corresponds to the total
reflection.Comment: 8 pages, 4 figure
Propagation of charged particle waves in a uniform magnetic field
This paper considers the probability density and current distributions
generated by a point-like, isotropic source of monoenergetic charges embedded
into a uniform magnetic field environment. Electron sources of this kind have
been realized in recent photodetachment microscopy experiments. Unlike the
total photocurrent cross section, which is largely understood, the spatial
profiles of charge and current emitted by the source display an unexpected
hierarchy of complex patterns, even though the distributions, apart from
scaling, depend only on a single physical parameter. We examine the electron
dynamics both by solving the quantum problem, i. e., finding the energy Green
function, and from a semiclassical perspective based on the simple cyclotron
orbits followed by the electron. Simulations suggest that the semiclassical
method, which involves here interference between an infinite set of paths,
faithfully reproduces the features observed in the quantum solution, even in
extreme circumstances, and lends itself to an interpretation of some (though
not all) of the rich structure exhibited in this simple problem.Comment: 39 pages, 16 figure
Active feedback scheme for minimization of helicity-dependent instrumental asymmetries
A method for the active feedback reduction of optical instrumental intensity asymmetries is presented. It is based on the fast chopping of two spatially separated beams of light with orthogonal linear polarizations that are recombined and passed through a quarter-wave plate to yield a single beam with rapidly flipping helicity. Active electro-optic feedback has been successfully employed to maintain this asymmetry below 10−5
Active feedback scheme for minimization of helicity-dependent instrumental asymmetries
A method for the active feedback reduction of optical instrumental intensity asymmetries is presented. It is based on the fast chopping of two spatially separated beams of light with orthogonal linear polarizations that are recombined and passed through a quarter-wave plate to yield a single beam with rapidly flipping helicity. Active electro-optic feedback has been successfully employed to maintain this asymmetry below 10−5
Near-threshold collisional dynamics in the \u3ci\u3ee\u3csup\u3e−\u3c/sup\u3ee\u3csup\u3e+\u3c/sup\u3ep\u3c/i\u3e system
We study e+-H(n) and Ps(n)-p collisions near the three-body breakup threshold and thresholds for the charge-transfer processes.We show that classical trajectoryMonte Carlo (CTMC) simulations for the three-body breakup agree reasonably well in this energy region with quantum-mechanical convergent close-coupling (CCC) calculations even if the initial hydrogen atom or positronium atom is in the ground state. The threshold behavior of the three-body breakup cross section in e+-H(1s) and Ps(1s)-p collisions agrees with the Wannier law with Klar’s exponent and obeys the classical scaling laws, although some deviation from the Klar-Wannier behavior is observed in the CCC results. Below the threshold the agreement between CTMC and CCC disappears. In particular the CTMC method fails completely for the processes of H formation in Ps(1s)-p collisions and Ps formation in e+-H collisions well below the three-body breakup threshold. For higher initial states the CTMC results below the threshold improve substantially, in accordance with the correspondence principle. This is explained by comparing the quantum-mechanical threshold laws with the classical laws
Ballistic matter waves with angular momentum: Exact solutions and applications
An alternative description of quantum scattering processes rests on
inhomogeneous terms amended to the Schroedinger equation. We detail the
structure of sources that give rise to multipole scattering waves of definite
angular momentum, and introduce pointlike multipole sources as their limiting
case. Partial wave theory is recovered for freely propagating particles. We
obtain novel results for ballistic scattering in an external uniform force
field, where we provide analytical solutions for both the scattering waves and
the integrated particle flux. Our theory directly applies to p-wave
photodetachment in an electric field. Furthermore, illustrating the effects of
extended sources, we predict some properties of vortex-bearing atom laser beams
outcoupled from a rotating Bose-Einstein condensate under the influence of
gravity.Comment: 42 pages, 8 figures, extended version including photodetachment and
semiclassical theor
Antiproton collisions with excited positronium
We present results of calculations of several processes resulting from positronium (Ps) collisions with antiprotons: antihydrogen formation, Ps breakup, and nPs-changing collisions. Calculations utilize the quantum convergent close-coupling (CCC) method and the classical trajectory Monte Carlo (CTMC) method. We identify a region of Ps principal quantum numbers nPs and Ps energies where the classical description is valid and where the CCC calculations become computationally too expensive. This allows us to present the most complete and reliable set of cross sections in a broad range of nPs and initial orbital momentum quantum numbers lPs which are necessary for experiments with antihydrogen at CERN
Electron scattering from molecules and molecular aggregates of biological relevance
In this Topical Review we survey the current state of the art in the study of low energy electron collisions with biologically relevant molecules and molecular clusters. We briefly describe the methods and techniques used in the investigation of these processes and summarise the results obtained so far for DNA constituents and their model compounds, amino acids, peptides and other biomolecules. The applications of the data obtained is briefly described as well as future required developments
Multiphoton detachment of electrons from negative ions
A simple analytical solution for the problem of multiphoton detachment from
negative ions by a linearly polarized laser field is found. It is valid in the
wide range of intensities and frequencies of the field, from the perturbation
theory to the tunneling regime, and is applicable to the excess-photon as well
as near-threshold detachment. Practically, the formulae are valid when the
number of photons is greater than two. They produce the total detachment rates,
relative intensities of the excess-photon peaks, and photoelectron angular
distributions for the hydrogen and halogen negative ions, in agreement with
those obtained in other, more numerically involved calculations in both
perturbative and non-perturbative regimes. Our approach explains the extreme
sensitivity of the multiphoton detachment probability to the asymptotic
behaviour of the bound-state wave function. Rapid oscillations in the angular
dependence of the -photon detachment probability are shown to arise due to
interference of the two classical trajectories which lead to the same final
state after the electron emerges at the opposite sides of the atom when the
field is close to maximal.Comment: 27 pages, Latex, and PostScript figures fig1.ps, fig2.ps, fig3.ps,
accepted for publication in Phys. Rev.
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