COLLISION-INDUCED 3-PHOTON IONIZATION

A semiclassical treatment of collision-induced three-photon ionization of atoms with a near two-photon resonance is presented. The system is described by an effective two-level system. The wavelength dependence of the ionization yield does not obey a power law. When the first excited state is far from resonance, and with a C6R6 interatomic potential, a first-order correction to the expected -32 power law obeys a-power law. This three-photon process promises to be an extremely sensitive method for the study of collisional effects in the far wing of two-photon S-S and S-D transitions, and without the requirement of high densities. © 1979 The American Physical Society.