XUV Attosecond Photoionization and Related Ultrafast Processes in Diatomic and Large Molecules

Abstract

The properties of matter are ultimately determined by its electronic structure. A suitable perturbation of the electrons' distribution from its equilibrium configuration in a system such as an atom, a molecule, or a solid, can therefore initiate certain dynamical processes. Intense and ultrashort light pulses are ideal tools for that purpose as their electric fields couple directly to the electrons. Therefore, they are not only able to distort the equilibrium electron distribution but, even allow driving a system on sub-femtosecond timescales with the light's Petahertz field-oscillations. This has been realized first in experiments that studied atoms in strong laser fields some 25 years ago. These experiments revealed a wealth of fundamentally important phenomena that are strictly timed to the laser-field oscillations such as the release of electrons by tunneling through the field-distorted Coulomb binding potential, or field-driven (re-)collisions of the released electrons with the atomic ion. The latter, in turn, led to the discovery of a range of essential secondary processes such as the generation of very high orders of harmonics of the driving light with photon energies that can extend into the X-ray range. Since then, thanks to a true revolution in laser technology, tremendous progress has been made in the field. Laser science has now reached a level of perfection where it is possible to produce intense light pulses with durations down to a single oscillation cycle and with virtually arbitrary evolution of the electric field in a wide range of frequencies. The availability of such field transients enabled a number of exciting possibilities, such as control over the breakage of selected chemical bonds in molecules by directly driving the molecular valence electrons that actually form the bond, or the production of coherent attosecond pulses in the soft X-ray wavelength range that can be used for probing or initiating dynamics on time-intervals during which the electronic distribution in the system under study stays essentially frozen. The recent years have seen a particularly vivid progress in the research of using ultrashort intense light pulses for controlling and probing ultrafast dynamics. On the one hand, a number of groups have extended the research field to systems with a much increased complexity and have studied and controlled field-induced dynamics in large polyatomic molecules, cluster complexes, bio-matter, nanoparticles and crystals, and also in condensed phase systems such as solid surfaces, v