Angular-distribution asymmetry parameters for photoelectrons produced by two-photon ionization of the Ar atom and two-photon detachment of the ${\mathrm{F}}^{\mathrm{-}}$ ion are calculated for photon energies below the thresholds for single-photon ionization and single-photon detachment, respectively. Effects of electron correlations are included by perturbative methods. Good agreement is obtained between our results and those of a recent experimental angular-distribution measurement of two-photon detachment of the ${\mathrm{F}}^{\mathrm{-}}$ ion at λ=532 nm [C. Blondel, M. Crance, C. Delsart, and A. Giraud (unpublished)].

• Received 13 December 1990

DOI:https://doi.org/10.1103/PhysRevA.44.324