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The European Physical Journal D

Elastic scattering of electrons by metastable hydrogen atoms in the presence of a resonant laser field

S. P. Purohit, Anoop K. Jain, K. C. Mathur

Published Jan 1, 1998• 4 citations
Publisher

Abstract

Within the framework of the rotating wave approximation the elastic scattering of electrons by metastable 2s state of hydrogen atoms is studied in the presence of a resonant laser field. The frequency of the circularly polarized laser field is chosen to match the 2s-3p transition frequency in the hydrogen atom. Variation of the cross section with laser intensity and with incident electron energy (50-150 eV) is investigated.

DOI
10.1007/s100500050088

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Dressed states of an atom in a classical laser field of frequency close to an atomic transition frequency are obtained, which are a considerable improvement over the usual two-level rotating-wave approximation. These wave functions are used in a calculation of the cross section for elastic electron-atom scattering in a laser field. Numerical calculations for electron-hydrogen scattering demonstrate that scattering involving absorption or emission of photons can be strongly influenced by coupling to the nonresonant states, regardless of the field strength. Inclusion of the counter-rotating terms in the calculation is shown to be essential for extending the applicability of the theory to scattering in nonresonant fields, where a first-order perturbation-theoretic treatment of the atom-field interaction would be expected to be quite justified.
The effect of the resonant structure in the continuous spectrum induced by an external laser field due to the coupling of continuum states with the 1s4s 1 S level in helium on cross sections of elastic and inelastic scattering of probe radiation on an atom in the metastable 1s2s 1 S state at an energy above the ionization threshold is theoretically studied. Explicit expressions for the angular distribution and the degree of polarization of scattered photons as functions of probe and laser radiation characteristics are derived in the rotating wave approximation. Frequency, angular, and polarization dependences of the cross sections of scattering into final 1s 2 1 S, 1 s2s 1 S, and 1s4s 1 S atomic states are calculated.
Process of photon scattering on atoms is considered at energy above the ionization threshold. Influence of the resonant structure in the continuum, induced by a laser field due to coupling with the level 41 S in helium, on the cross sections of elastic and inelastic scattering of a probe radiation on atom in the meta-stable state 21 S is theoretically investigated. In the rotating wave approximation approach dependences of resonant scattering cross sections on the probe and laser radiation characteristics are obtained. The frequency and polarization dependences of the scattering cross sections to the final states of atom 11 S, 21 S and 41 S are calculated.
We consider electron scattering by hydrogen atoms in a bichromatic linearly polarized laser field of frequencies ω and 3ω and we discuss the coherent control of the scattering process as a function of the relative phase φ between the two components of the radiation field. The electrons are assumed to have sufficiently high energies in order to permit the description of the scattering process in the first-order Born approximation. The scattered electrons, embedded in the bichromatic laser field of moderate power, as well as the laser dressing of the hydrogen atoms in their ground state are described by time-dependent perturbation theory. We discuss the angular dependence of the nonlinear differential scattering cross sections for the low values N = ±2 of absorbed or emitted laser photons as a function of the relative phase φ between the two radiation field components. We also compare our results with those obtained from the assumption of a static potential describing the target atom.