Multiphoton Ionization of Atoms

Abstract

This chapter provides an overview of multiphoton ionization of atoms. Multiphoton ionization—a special kind of multiphoton transition—can be described at a moderately light power density using the formalism of the time-dependent perturbation theory. The distortion of the atomic structure plays an especially important role in the multiphoton ionization of rare gases. The influence of distortion on multiphoton ionization can be investigated in the case of multiphoton resonance. This means that the energy of one atomic state coincides with the energy of some quanta. The multiphoton ionization rate can be expressed as the product of the rate of multiphoton excitation and that of subsequent ionization of the resonant level (two-step process). The rate of multiphoton excitation is especially sensitive to the shift of the resonance level, that is, the distortion of the atomic structure. The characteristics of multiphoton ionization reflect not only the feature of the atomic structure but the feature of the ionizing field. In this chapter, lowest order perturbation theory of multiphoton ionization is discussed. Multiphoton ionization of rare gases are elaborated. Concepts related to strong field photoemission are also discussed.