Aurelia Cionga

Circular dichroism in free-free transitions of high-energy electron-atom scattering

We consider high energy electron scattering by hydrogen atoms in the presence of a laser field of moderate power and higher frequencies. If the field is a superposition of a linearly and a circularly polarized laser beam in a particular configuration, then we can show that circular dichroism in two photon transitions can be observed not only for the differential but also for the integrated cross sections, provided the laser-dressing of the atomic target is treated in second order perturbation theory and the coupling between hydrogenic bound and continuum states is involved.

Electron-atom scattering in a circularly polarized laser field

We consider electron-atom scattering in a circularly polarized laser field at sufficiently high electron energies, permitting us to describe the scattering process by a first-order Born approximation. Assuming the radiation field has sufficiently moderate intensities, the laser dressing of the hydrogen target atom in its ground state will be treated in second-order perturbation theory. Within this approximation scheme, it is shown that the nonlinear differential cross sections of free-free transitions do not depend on the dynamical phase

Two-colour three-photon ionization of hydrogen

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Dichroism in high energy electron-hydrogen scattering in an elliptically polarized laser field

of the radiative process nor on the helicity of the circularly polarized laser light. Relations to the corresponding results for linear laser polarization are established.

Rayleigh scattering fromn=3 states of hydrogenlike atoms

Based on analytical equations valid in perturbation theory, we study the process of ionization of the ground state of the hydrogen atom by the absorption of three photons, two of them being of the same frequency. Results are given for the total ionization rate and for the angular distribution of the ejected electrons, in a regime of frequencies in which two-colour two-photon ionization is not possible. The case of orthogonal photon polarizations, investigated in some detail, displays a strong dependence on the electron direction.

Dichroic effects in the two-colour, two-photon ionization of hydrogen

Abstract We consider electron–hydrogen scattering in an elliptically polarized laser field. The electrons are sufficiently energetic so that the scattering process can be treated in the first order Born approximation. The effect of elliptic dichroism in the angular distribution of the scattered electrons for small values N of emitted or absorbed laser photons is considered as a function of the ellipticity ξ of the laser field for a fixed scattering angle θ as a function of the azimuthal angle ϕ . For electrons of high energy, dichroism can only be observed when the laser-dressing of the atomic target is taken into account in second order time-dependent perturbation theory permitting virtual bound–continuum transitions.

Circular dichroism in hydrogen multiphoton ionization by a bichromatic field of frequencies ω and 3ω

An exact analytic evaluation of the Kramers-Heisenberg matrix elements for Rayleigh scattering fromn=3 states of hydrogenlike atoms is performed in the nonrelativistic dipole approximation, using the Greens function method. The results are given separately for each subshell. The possibility of 3s↔3d transitions is also considered. The dependence on the photon energy is contained in six invariant amplitudes. The formulas needed for the evaluation of the various cross sections are presented. The numerical results are contained in tables from which partial and total cross sections can be easily built, covering the energy range from zero up to 20 times theK threshold energy. In the vicinity of Balmerα frequency the cross section is large and comparable with that for excitedn=2 states, confirming an earlier hypothesis of Röhr. At other energies the cross sections forn=2 andn=3 states are comparable, too. The results should be useful in plasma diagnostics.

Elliptic Dichroism in Angular Distributions in Free-Free Transitions in Hydrogen

Abstract We study dichroic effects in the two-photon ionization of hydrogen from its ground state due to the interaction with a bichromatic field of commensurate frequencies. The two field components have different polarization: one is linearly polarized and the other is circularly polarized. Circular dichroism in the angular distribution of the photoelectrons appears if the helicity of the circularly polarized field is reversed. Numerical results reveal the influence of the photon frequencies chosen on the circular dichroism in the azimuthal angular distribution of the ejected photoelectrons.

State dependence of rayleigh scattering from an=2 state of hydrogenlike atoms

The dichroic effects in the multiphoton ionization of the ground state hydrogen atom by a coherent superposition of a laser beam and its third harmonic, are studied via perturbative calculations. The final state of the photoelectrons, which has the energy E = E1 + 3ω (E1 the ground state energy and ω the laser frequency), is reached by two interfering quantum paths: (a) absorption of one harmonic photon and (b) absorption of three laser photons. In the chosen regime of field intensities, the radiative corrections to the absorption of one harmonic photon may be disregarded. Our numerical results illustrate the influence of the laser frequency, of the relative intensity and of the harmonic phase upon the dichroic signal.

Target dressing effects in laser-assisted x-ray photoionization.

Dichroism is a well known concept in classical optics where it denotes the property shown by certain materials of having absorption coefficients which depend on the state of polarization of the incident light 1. This concept has been extended to the case of atomic or molecularinteractions with a radiation field. In particular, the notion of ellipticdichroism in angular distribution (EDAD) refers to the difference between the differential cross sections (DCS) of laser assisted signals for left and right elliptically polarized (EP) light 2.