Calculation of frequency-dependent polarizabilities with application to photodetachment threshold shift in a strong laser field

Calculations of the frequency-dependent electric dipole polarizabilities have been carried out for atomic Cl and ${\mathrm{Cl}}^{\mathrm{-}}$ using many-body perturbation theory. Higher-order diagrams have been evaluated to include the effects of electron correlation. These results are used to interpret a recent experimental observation of shifts in the photodetachment threshold of ${\mathrm{Cl}}^{\mathrm{-}}$ in the presence of a strong laser field.