Multiphoton Processes in Atoms

1. Introduction.- 2. AC-Stark Shift of Atomic Levels.- 2.1 Single-Level Quantum System.- 2.2 The Linear Stark Shift for a Hydrogen Atom in an Oscillating Field.- 2.3 Atomic Response to an External Oscillating Field.- 2.4 The Perturbation of Non-Degenerate Atomic States in a Weak Field.- 2.5 Perturbation of the Hydrogen Atom Spectrum in a Strong Field.- 2.6 Perturbation of Rydberg States in a Weak Field.- 2.7 Stark Effect in a Super-Atomic Radiation Field.- 2.8 The Stark Atom.- 2.9 AC-Stark Shift in Negative Ions.- 2.10 Dynamical Stark Resonance.- 2.11 AC-Stark Shift and Ionization.- 3. Ionization of a Particle with a Short-Range Potential Well.- 3.1 The Keldysh-Faisal-Reiss Approximation.- 3.2 Model One-Particle Potentials of Negative Ions.- 3.3 Residual Interaction Between Electrons.- 3.4 Removal of Internal Electrons from Negative Ions.- 3.5 Numerical Solutions for the Strong-Field Case.- 3.6 Experiments on Multiphoton Detachment of Negative Ions.- 4. Tunneling Ionization of Atoms.- 4.1 Landau-Dykhne Adiabatic Approximation.- 4.2 Rates of Tunneling Ionization for Atoms and Ions.- 4.3 Energy Spectrum of Electrons.- 4.4 Above-Barrier Decay of Atoms.- 4.5 Experimental Data and Interpretation.- 4.6 Relativistic Effects.- 5. Direct (Nonresonant) Multiphoton Ionization of Atoms.- 5.1 Multiphoton Ionization of Hydrogen Atom.- 5.2 Alkali Atoms.- 5.3 Atoms with Many Valence Electrons.- 6. Resonance-Enhanced Ionization.- 6.1 Resonance-Enhanced Ionization in a Weak Field.- 6.2 Field Effects in Resonance-Enhanced Ionization.- 6.3 Angular Distributions of Photoelectrons in Resonance- Enhanced Multiphoton Ionization of Atoms.- 6.4 Exotic Resonances.- 6.5 Resonances with Autoionizing States.- 6.6 Further Experiments.- 7. Above-Threshold Ionization of Atoms.- 7.1 The Nature of Above-Threshold Multiphoton Ionization.- 7.2 Compound Matrix Elements for Processes of Kth and (K+ 1)th Orders.- 7.3 WKB Estimates of Dipole Matrix Elements.- 7.4 A Critical Field.- 7.5 Two-Photon Above-Threshold Ionization of a Hydrogen Atom by Radiation of Less than Critical Intensity.- 7.6 Multiphoton Above-Threshold Ionization of a Hydrogen Atom by Radiation of Less than Critical Intensity.- 7.7 Experimental Aspects. Parameters that Influence the Photoelectron Spectra.- 7.8 Experimental Data for I < Ic.- 7.9 Theoretical Description of Above-Threshold Ionization at I < Ic.- 7.10 Experimental Data for I > Ic and Their Interpretation.- 7.11 Theoretical Interpretation of Electron Energy Spectra for I > Ic.- 7.12 Above-Threshold Ionization by Ultra-Short Laser Pulses.- 7.13 Other Effects.- 8. Multiple Ionization of Atoms.- 8.1 Mechanisms of Multiple Ionization.- 8.2 Stepwise Production of Multiply Charged Ions.- 8.3 Simultaneous Detachment of Several Electrons.- 8.4 Detachment of Electrons from Inner Shells of Atoms and Ions.- 8.5 Multiple Ionization of Atoms in the Tunneling Limit.- 8.6 Production of Multiply Charged Ions in Laser Fields of Subatomic and Superatomic Intensity.- 8.7 Summary.- 9. Ionization by Fields of Subatomic Strength.- 9.1 Definition of an Atomic Field.- 9.2 Ionization of Atoms and Atomic Ions at F ? Fa and ? > 1.- 9.3 Above-Barrier Decay of an Atom at F > Fa.- 10. Atoms in Superintense Laser Fields.- 10.1 Qualitative Picture of Atomic Stabilization.- 10.2 Keldysh-Reiss Approach for a Superintense Field.- 10.3 Numerical Calculations of Ionization Rates.- 10.4 The Kramers-Henneberger Method.- 10.5 Numerical Solutions of Newton Equations.- 10.6 Stabilization of a Rydberg Atom in a Superintense Field.- 10.7 Stark Atom.- 10.8 Collapse and Revival of aPopulation Inversion in a Superintense Field.- 11. Related Phenomena.- 11.1 Microwave Ionization of Atoms.- 11.2 Multiphoton Ionization of Polarized Atoms.- 11.3 Nonlinear Ionization by Non-Classical Light.- 11.4 Excitation of High Optical Harmonics.- References.