Elliptic and Circular Dichroism Effects in Two-Photon Double Ionization of Atoms

An ab initio parametrization of the two-photon double ionization amplitude from an s{sup 2} subshell of an atom in a {sup 1}S state is presented and used to predict two light polarization effects on photoelectron angular distributions that do not exist in single-photon double ionization: (i) elliptic dichroism and (ii) circular dichroism at equal energy sharing. Estimates for He show large magnitudes for these effects, which provide a means for polarization control of double ionization by vacuum ultraviolet light.