Elliptic dichroism and angular distribution of electrons in two-photon ionization of atoms

The three-dimensional angular distribution of electrons in two-photon ioniz ation of atoms by an elliptically polarized laser beam, from an initial sta te with arbitrary angular momentum J(i), is expressed in terms of six frequ ency-dependent invariant atomic parameters. The specific effect of the fiel d polarization on the angular distribution (the elliptic dichroism, ED) is discussed for the general case of elliptic polarization. The necessary cond itions for a non-zero ED are established and its physical origin is explain ed. The general theory is illustrated by a simple analytical calculation fo r the delta-potential model. Numerical calculations of the angular distribu tion parameters for H and Cs atoms are also performed and the dependence of ED magnitude on the atomic quantum numbers and the photon frequency is dis cussed for different frequencies.