Differential rate for non-sequential multi-photonionization of helium for equal sharing of energy by the electrons in intense laser field

Abstract

Angular triple differential rate for helicity dependent spin-current generation in nonsequential multi-photon ionization of He with equal sharing of kinetic energy by circularly polarized
intense laser field is computed in a field theoretic way. The initial state is taken as the product of space-symmetric correlated wave function of He(1s2) multiplied by the product of the anti-symmetric Dirac-spinors. The two final electrons can be either in the singlet or in the triple state. We found only singlet state contributes for equal sharing of energy by the the final electrons. These electrons may be emitted with spin-directions as that of the bound-electrons (symmetric transition) or with spindirections reversed (spin-flip transition). Symmetric transition rate is found to be higher than the flip
transition rate. The spin-current depends on intensity, helicity, frequency of the beam and number of photons absorbed. At low intensity where ponderomotive potential is low present angular differential cross-section compares fairly well with the only existing non-relativistic result obtained using lowest
order perturbation theory.