Cross Sections of Direct Multiphoton Ionization of Atoms

Abstract

Publisher Summary This chapter discusses the cross sections of direct multiphoton ionization of atoms (multiphoton cross sections) and the methods used to measure these cross sections. The experimental results and the theoretical relations, enables to estimate the magnitude of multiphoton cross sections. Knowledge of the cross sections of direct multiphoton ionization of atoms enables one to obtain information about observed phenomena, such as (1) ionization probability, (2) the number of ions produced, (3) the ionization degree of initial neutral medium, and (4) how all these quantities depend upon different parameters characterizing the radiation, and the atom medium. There are many areas in the physics of laser radiation interaction with matter where one has to know the probability of multiphoton atom ionization or at least its approximate estimate. Rigorous theories of the ionization process require complicated calculations for each atom and each radiation frequency. The chapter presents the approximate relations that are absolutely elementary but on the other hand, it gives a satisfactory description of the experimental data. The chapter considers the principal features of the process of multiphoton atom ionization. The process of ionization of atomic particles (atoms, molecules, and ions) under the action of radiation is called “nonlinear,” if the energy ћω of radiation quanta is less than the binding energy ℇ n , of an electron in a given particle (less than the ionization potential l if the particle is in its ground state).