ABSTRACT
A number of scientific and technological drivers are responsible for contemporary interest in studies concerned with how light and matter interact with each other, particularly with how very intense light interacts with matter. Much of the importance attributed to this area of research stems from the recognition that very intense light has very strong fields associated with it, and the dynamics that ensue when such fields irradiate atoms and molecules are of interest from both fundamental and applied viewpoints. It is useful to begin the discussion of such dynamics by first establishing what the terms “strong field” and “intense light” mean in relation to some physically established standard. One useful benchmark that may be adopted for this purpose is the Coulombic field that is experienced by an electron in the 1-s orbital of the hydrogen atom: it has a value of ~109 V cm-1. The intensity of light that would give rise to such a field is 1016 W cm-2 (or 10 PW cm-2). Pulses of light of such intensity are readily generated using commercially available Ti:sapphire laser systems incorporating an oscillator and an amplifier. Such systems emit 800-nm
6.1 Introduction ....................................................................................................99 6.2 Ultrashort Pulses........................................................................................... 101 6.3 Molecular Ionization and Dissociation ......................................................... 103 6.4 TDBO Approximation and TDPES .............................................................. 107 Acknowledgments .................................................................................................. 111 References .............................................................................................................. 111
light, typically with pulse durations of 100 fs or less. It is not difficult to imagine that extremely high photon densities can be achieved, on the order of 1036 photons s-1 cm-2, by focusing light from such femtosecond lasers. It is these remarkably high photon densities that mediate the essentially nonlinear nature of light-matter interactions in what has come to be known in recent years as the strong-field regime. In the context of what is to follow in this chapter, matter comprises individual atoms and molecules. The magnitude of the optical field that is experienced by these atoms and molecules ensures that the interaction cannot be considered perturbative. In the following, we present an overview of how the nonlinear nonperturbative dynamics of atoms and molecules in the strong-field regime is investigated using contemporary experimental and theoretical techniques.
