The development of lasers capable of producing high-intensity pulses has opened a new area in the study of light-matter interactions. The corresponding laser fields are strong enough to compete with the Coulomb forces in controlling the dynamics of atomic systems and give rise to multiphoton processes. This book presents a unified account of this rapidly developing field of physics. The first part describes the fundamental phenomena occurring in intense laser-atom interactions and gives the basic theoretical framework to analyze them. The second part contains a detailed discussion of Floquet theory, the numerical integration of the wave equations and approximation methods for the low- and high-frequency regimes. In the third part, the main multiphoton processes are discussed: multiphoton ionization, high harmonic and attosecond pulse generation, and laser-assisted electron-atom collisions. Aimed at graduate students in atomic, molecular and optical physics, the book will also interest researchers working on laser interactions with matter.

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An analysis of the influence of the magnetic field of an intense, high-frequency laser pulse on the stabilization of an atomic system is presented. We demonstrate that at relatively modest intensities the magnetic field can significantly alter the dynamics of the system. In particular, a breakdown of stabilization occurs, thereby restricting the intensity regime in which the atom is relatively stable against ionization. Counterpropagating pulses do not negate the detrimental effects of the magnetic field. We compare our quantum mechanical results with classical Monte Carlo simulations. PACS numbers: 32.80.Fb, 32.80.Rm, 42.50.Hz Theoretical studies of atoms interacting with highfrequency intense laser pulses have predicted a significant decrease in the ionization probability with increasing laser intensity. This phenomenon is referred to as atomic stabilization, and has been extensively studied over the past decade [1]. Many aspects of this phenomenon can be understood by performing a Kramers-Henneberger (KH) transformation to the rest frame of a classical electron in the laser field. In particular, by developing a highfrequency Floquet theory in the KH frame [2], stabilization can be seen to have its origin in the rapid quiver motion of the atomic electron in the laser field. This allows the electron dynamics to be described by an effective potential that, on average, localizes the electron away from the vicinity of the nucleus. Subsequent ab initio Floquet calculations confirmed that ionization rates decrease with increasing intensity in a high-frequency field [3]. By directly integrating the time-dependent Schrödinger equation numerically, simulations in one [4] and three dimensions [5] demonstrated reductions in the ionization probability with increasing laser intensity when an atom interacts with realistic laser pulses having a finite duration. Further work has been carried out in order to elucidate the effects of the pulse shape and duration [6,7]. We also note that evidence of atomic stabilization of Rydberg states has been observed experimentally [8].In the above-mentioned theoretical studies, the magnetic component of the laser pulse was neglected. However, as the laser intensity increases, relativistic effects that alter the stabilization dynamics become important. Classical Monte Carlo simulations have indicated that the magnetic field pushes the electron in the laser pulse propagation direction, reducing the degree of stabilization [9]. Relativistic wave equations have also been considered within the context of reduced dimensional models [10,11]. However, it is also of interest to study the effects that are neglected in the dipole approximation by using the fully space-and time-dependent vector potential in the nonrelativistic Schrödinger equation [12]. For atomic hydrogen, this results in the cylindrical symmetry of the system being broken, thereby requiring a fully three-dimensional calculation to be carried out for extremely high laser intensities. This is a computationally demanding task. Howev...