Multiphoton detachment of halogen negative ions with elliptically polarized light

Multiphoton excitation with elliptically polarized light brings out more information in the photodetachment or photoionization processes than linearly polarized light. This information can be reached by recording photoelectron angular distributions for several values of the ellipticity angle, and fitting the whole set of data with an analytic formula. We give here the appropriate formula, valid for any number N of exciting photons, with the assumptions of (1) an initially even and momentumless (J equals 0) atom or ion and (2) that after excitation of an electron, the residual core be left in an odd state. These are the conditions met by multiphoton detachment from halogen negative ions. With elliptically polarized light of λ equals 1064.2 nm, we have measured the angular distributions of three-photon detached electrons from the ion I^-, and four-photon detached electrons from Cl^- and F^-. The experimental results are quantitatively analyzed and commented on.