Simultaneous electron-photon excitation of hydrogen and helium

Abstract

Total and differential cross sections for simultaneous excitation of H(2s), H(3s) and He(ls2s) by electron impact in the presence of a photon field have been calculated in second-order perturbation theory. The characteristics of the results are interpreted in terms of their physical origin. The off-shell excitation cross section for the He(ls2s) state is found to be one order of magnitude smaller than that for excitation of the H(2s) state. This is consistent with our expection that atoms with higher dipole-polarisability should favour larger off-shell cross sections for transitions between s-states.

Effects of laser polarization in laser-assisted electron-helium inelastic collisions: a Sturmian approach

“…In order to illustrate the effects of the laser polarization on the variations of the differential cross sections, we have chosen to compare our results obtained for F 0 //K Before presenting the results of our calculations, we want to make a remark concerning the phase γ k used in equations (6), (7), (11) and (12) In figure 2(a) and figure 2(b), we show the laser-assisted differential cross sections corresponding to 1 1 S → → 2 1 S excitation process. The complete result obtained by using the scattering amplitude Eq.…”

Spin dynamics in nonsequential two-photon double ionization of helium in an intense laser field

“…We address here the benchmark questions of circular dichroism and spin asymmetry in two-photon NSDI of He in an intense laser field using field theory and a relativistic approach. The work also provides a platform to validate the adequacy of the space-correlated wave function [6], of He (1s 2 ) and its present relativistic extension to include Dirac spinors. Multiphoton ionization of atoms of H and He (single ionization) in an intense laser field is computed previously [3][4][5] using a time-reversed S matrix and a relativistic Keldysh-Faisal-Reiss (KFR) approach.…”

“…Helicity-dependent spin asymmetry in angular distribution is found in the triple differential rate (TDRT). CD is obtained in TPDI of He for ejection of equal-energy electrons in different angular directions; however, CDis known to vanish [6,7] in the case of single-photon double ionization (SPDI).…”

R-matrix Floquet study of simultaneous electron-photon excitation of helium in a CO2laser field

“…This process, known as simultaneous electron-photon excitation (SEPE), has been studied experimentally by a number of groups, using rare gas atom targets in a CO 2 or a Nd:YAG laser field [1][2][3][4][5][6]. Relatively few theoretical studies have been performed, and most of these are based on extensions to the lowfrequency approximation (LFA) [7,8], perturbation theory [9] or a semi-classical instantaneous collision approximation (ICA) [10], which relate the laser-assisted cross sections to those for fieldfree scattering in a relatively simple way. In contrast, the R-matrix Floquet (RMF) theory [11] provides a rigorous, ab initio and non perturbative approach to laser-assisted electron scattering by a general atomic target.…”