Three-photon ionization of lithium

We study three-photon ionization of neutral lithium, in the presence of a strong laser light intensity of up to 15 GW cm(-2), involving the absorption of three photons combined in such a way that first we have one-photon resonant plus two photon non-resonant ionization transitions, then the reverse case is studied. The resolvent operator formalism and projection operators are used in the calculations. An atomic central field model potential is used to generate orbital wavefunctions. We compare our calculations with previous calculations done by Chang and Poe [Phys. Rev. A 16 (1977) 606] for non-resonant three-photon ionization rates of lithium, with which we obtained a very good agreement. (C) 1998 Published by Elsevier Science B.V.