Atoms in strong radiation fields are interesting objects for study, and the research field that concerns itself with this study is a comparatively young one. For a long period after the ~scovery of the photoelectric effect. it was not possible to generate electro magnetic fields that did more than perturb the atom only slightly, and (first-or~er) perturbation theory could perfectly explain what was going on at those low intensities. The development of the pulsed laser bas changed this state of affairs in a rather dramatic way, and fields can be applied that really have a large, or even dominant influence on atomic structure. In the latter case, w~ speak of super-intense fields. Since the interaction between atoms and electromagnetic waves is characterized by many parameters other than the light intensity, such as frequency, iQnization potential, orbit time, etc., it is actually quite difficult to define what is exactly meant by the term 'super-intense'. Obviously the term does not have an absolute meaning, and intensity should always be viewed in relation to other properties of the system. An atom in a radiation field can thus best be described in terms of various ratios of the quantities involved. The nature of the system sometimes drastically changes if the value of one of these parameters exceeds a certain critical value, and the new regime could be called super-intense with respect to that parameter.

The study of atomic systems exposed to super-intense laser fields de fines an important area in atomic, molecular and optical physics. Although the concept of super-intense field has no absolute meaning, it is now usual to call an electromagnetic field super-intense when it exceeds the atomic binding field. In the case of the simplest atomic system, hydrogen in its 16 2 ground state, this occurs above an intensity of 3. 5 x 10 Wattfcm which is the atomic unit of intensity. Presently at the laboratory scale and in ex tremely short and tightly focussed laser pulses, the electric field strength 16 18 2 reaches peak values which are of the order of 10 - 10 Wattfcm in the infrared frequency regime, the prospect being that such peak intensities may be reached within a few years in a regime of much higher frequencies (XUV or even X). The interaction of such electromagnetic fields with an atomic system has a highly non-linear character which has led to the observation of to tally unexpected phenomena. There are three fundamental processes which have marked the beginning of an intensive research in the field of super intense laser-atom physics (SILAP). These processes which only involve one atomic electron are (i) the so-called above-threshold ionisation i. e.

The rapid development of powerful pulsed lasers is at the origin of a conside rable interest in studying the response of an atom, a molecule (or a solid) to a strong electromagnetic field. It is now possible to produce at the laboratory scale, ultra-short 13 pulses with a duration of 100 femtoseconds (10- second) and a power of the order 12 of 1 terawatt (10 Watt). Under these conditions, very high peak intensities may be obtained and electric fields exceeding typical electron binding fields in atoms are generated. The interaction of an atom or a molecule with such electromagnetic fields has a highly non-linear character which leads to unexpected phenomena. Amongst them, - above-threshold ionization (ATI) i.e. the absorption of additional photons in excess of the minimal number necessary to overcome the ionization potential and its molecular counterpart, above-threshold dissociation (ATD); - generation of very high harmonics of the driving field; - stabilization of one-electron systems in strong fields. These processes were the main topics of two international meetings which were held in 1989 and 1991 in the United States under the common name SILAP (Super-Intense Laser-Atom Physics).

A unified account of the rapidly developing field of high-intensity laser-atom interactions, suitable for both graduate students and researchers.

This book covers a diverse cross section of this interdisciplinary research field, with contributions grouped into four categories: laser-induced filamentation; atoms and molecules in a laser field; interaction of solid materials with a coherent light field; and ion acceleration and ionization of atoms in super intense laser fields. This book series presents up-to-date reviews of advances in this interdisciplinary research field, spanning atomic and molecular physics, as well as molecular and optical science, which have been stimulated by the recent developments in ultrafast laser technologies. Each book compiles peer-reviewed articles by researchers at the forefront of their particular subfields. All the chapters include an overview to allow graduate students and researchers unfamiliar with the subfield to grasp the importance and attractions of the topic covered, followed by reports of cutting-edge discoveries.

This series, established in 1965, is concerned with recent developments in the general area of atomic, molecular, and optical physics. The field is in a state of rapid growth, as new experimental and theoretical techniques are used on many old and new problems. Topics covered also include related applied areas, such as atmospheric science, astrophysics, surface physics, and laser physics.Articles are written by distinguished experts who are active in their research fields. The articles contain both relevant review material as well as detailed descriptions of important recent developments.

It is a great pleasure that we are now publishing the fourth volume of the series on PUILS, through which we have been introducing the progress in ultrafast intense laser science, the frontiers of which are rapidly expanding, thanks to the progress in ultrashort and high-power laser technologies. The interdisciplinary nature of this research ?eld is attracting researchers with di?erent expertise and backgrounds. As in the previousvolumeson PUILS, each chapter in the presentvolume, which is in the range of 15–25 pages, begins with an introduction in which a clear and concise account of the signi?cance of the topic is given, followed by a description of the authors’ most recent research results. All the chapters are peer-reviewed. The articles of this fourth volume cover a diverse range of the interdisciplinary research ?eld, and the topics may be grouped into four categories: strong ?eld ionization of atoms (Chaps. 1–2), excitation, ioni- tion and fragmentation of molecules (Chaps. 3–5), nonlinear intense optical phenomena and attosecond pulses (Chaps. 6–8), and laser solid interactions and photoemissions (Chaps. 9–11).