Calculation of the free-free transitions in the electron-hydrogen scattering S-wave model

The S-wave model of electron-hydrogen scattering is evaluated using the convergent close-coupling method with an emphasis on scattering from excited states including an initial state from the target continuum. Convergence is found for discrete excitations and the elastic free-free transition. The latter is particularly interesting given the corresponding potential matrix elements are divergent

Phase-matching conditions for nonlinear frequency conversion by use of aligned molecular gases

Includes bibliographical references (page 348).Transient birefringence can be induced in a gas of anisotropic molecules by an intense polarized laser pulse. We propose to use this birefringence to phase match nonlinear optical frequency-conversion processes. The conditions for anisotropic phase matching are derived, and experimental conditions required for phase-matched third-harmonic generation in a gas-filled hollow-core fiber are presented. We show that these conditions are experimentally feasible over a significant parameter range, making possible a new type of nonlinear optics

A study of cross sections for excitation of pseudostates

Using the electron-hydrogen scattering Temkin-Poet model we investigate the behavior of the cross sections for excitation of all of the states used in the convergent close-coupling (CCC) formalism. In the triplet channel, it is found that the cross section for exciting the positive-energy states is approximately zero near-threshold and remains so until a further energy, equal to the energy of the state, is added to the system. This is consistent with the step-function hypothesis [Bray, Phys. Rev. Lett. {\bf 78} 4721 (1997)] and inconsistent with the expectations of Bencze and Chandler [Phys. Rev. A {\bf 59} 3129 (1999)]. Furthermore, we compare the results of the CCC-calculated triplet and singlet single differential cross sections with the recent benchmark results of Baertschy et al. [Phys. Rev. A (to be published)], and find consistent agreement.Comment: Four pages, 5 figure

Spin-resolved electron-impact ionization of lithium

Electron-impact ionization of lithium is studied using the convergent close-coupling (CCC) method at 25.4 and 54.4 eV. Particular attention is paid to the spin-dependence of the ionization cross sections. Convergence is found to be more rapid for the spin asymmetries, which are in good agreement with experiment, than for the underlying cross sections. Comparison with the recent measured and DS3C-calculated data of Streun et al (1999) is most intriguing. Excellent agreement is found with the measured and calculated spin asymmetries, yet the discrepancy between the CCC and DS3C cross sections is very large

Hyperspherical partial wave theory applied to electron hydrogen-atom ionization calculation for equal energy sharing kinematics

Hyperspherical partial wave theory has been applied here in a new way in the calculation of the triple differential cross sections for the ionization of hydrogen atoms by electron impact at low energies for various equal-energy-sharing kinematic conditions. The agreement of the cross section results with the recent absolute measurements of R\"oder \textit {et al} [51] and with the latest theoretical results of the ECS and CCC calculations [29] for different kinematic conditions at 17.6 eV is very encouraging. The other calculated results, for relatively higher energies, are also generally satisfactory, particularly for large $\Theta_{ab}$ geometries. In view of the present results, together with the fact that it is capable of describing unequal-energy-sharing kinematics [35], it may be said that the hyperspherical partial wave theory is quite appropriate for the description of ionization events of electron-hydrogen type systems. It is also clear that the present approach in the implementation of the hyperspherical partial wave theory is very appropriate.Comment: 16 pages, 9 figures, LaTeX file and EPS figures. To appear in Phys. Rev.

A quasi classical approach to electron impact ionization

A quasi classical approximation to quantum mechanical scattering in the Moeller formalism is developed. While keeping the numerical advantage of a standard Classical--Trajectory--Monte--Carlo calculation, our approach is no longer restricted to use stationary initial distributions. This allows one to improve the results by using better suited initial phase space distributions than the microcanonical one and to gain insight into the collision mechanism by studying the influence of different initial distributions on the cross section. A comprehensive account of results for single, double and triple differential cross sections for atomic hydrogen will be given, in comparison with experiment and other theories.Comment: 21 pages, 10 figures, submitted to J Phys

Measurements of the ionization of atomic hydrogen by 17.6-eV electrons

We report triply differential measurements of atomic hydrogen ionization by 17.6-eV electrons, with the outgoing electrons both having 2 eV energy. These measurements supersede some of the existing data. The complete set is critically analyzed and is found to be much more internally consistent than before, thereby providing one of the most stringent tests for theory to date. Comparison with the calculations from the exterior complex scaling and convergent close-coupling theories shows excellent overall agreement in both shapes and magnitude

Solving the three-body Coulomb breakup problem using exterior complex scaling

Electron-impact ionization of the hydrogen atom is the prototypical three-body Coulomb breakup problem in quantum mechanics. The combination of subtle correlation effects and the difficult boundary conditions required to describe two electrons in the continuum have made this one of the outstanding challenges of atomic physics. A complete solution of this problem in the form of a "reduction to computation" of all aspects of the physics is given by the application of exterior complex scaling, a modern variant of the mathematical tool of analytic continuation of the electronic coordinates into the complex plane that was used historically to establish the formal analytic properties of the scattering matrix. This review first discusses the essential difficulties of the three-body Coulomb breakup problem in quantum mechanics. It then describes the formal basis of exterior complex scaling of electronic coordinates as well as the details of its numerical implementation using a variety of methods including finite difference, finite elements, discrete variable representations, and B-splines. Given these numerical implementations of exterior complex scaling, the scattering wave function can be generated with arbitrary accuracy on any finite volume in the space of electronic coordinates, but there remains the fundamental problem of extracting the breakup amplitudes from it. Methods are described for evaluating these amplitudes. The question of the volume-dependent overall phase that appears in the formal theory of ionization is resolved. A summary is presented of accurate results that have been obtained for the case of electron-impact ionization of hydrogen as well as a discussion of applications to the double photoionization of helium