We introduce a microscopic particle-in-cell approach that allows bridging the microscopic and macroscopic realms of laser-driven plasma physics. As a first application, resonantly driven cluster nanoplasmas are investigated. Our analysis reveals an attosecond plasma-wave dynamics in clusters with radii R is approximately equal to 30 nm. The plasma waves are excited by electrons recolliding with the cluster surface and travel toward the center, where they collide and break. In this process, energetic electron hot spots are generated along with highly localized attosecond electric field fluctuations, whose intensity exceeds the driving laser by more than 2 orders of magnitude. The ionization enhancement resulting from both effects generates a strongly nonuniform ion charge distribution. The observed nonlinear plasma-wave phenomena have a profound effect on the ionization dynamics of nanoparticles and offer a route to extreme nanoplasmonic field enhancements.

In the past few years, there has been a growing interest for direct-field electron acceleration with ultra-intense and ultrafast radially polarized laser beams. This particular acceleration scheme offers the possibility of producing highly collimated mono-energetic relativistic attosecond electron pulses from an initial cloud of free electrons that could be produced by ionizing a nanoparticle. In this paper, we describe how electron energy scales with laser power and we explain how the beam waist size and the pulse duration can be optimized for maximal acceleration. The main conclusion of our work is that an electron can effectively reach the high-intensity optical cycles of this particular beam and be optimally accelerated without the necessity of being released by photoionization near the pulse peak.

In this paper we describe how relativistic attosecond electron pulses could be produced in free space by ultrafast and ultraintense transverse magnetic (TM) laser beams. Numerical solutions of the time-dependent three-dimensional Maxwell-Lorentz equations reveal that electrons initially at rest at the waist of a multi-TW pulsed TM01 laser beam can be accelerated to multi-MeV energies. The use of a few-cycle laser beam and a compact initial electron cloud forces the particles to effectively interact with a single half-cycle of the laser field and form a pulse of attosecond duration.

In this paper we describe a laser acceleration scheme where an electron is accelerated from rest to GeV energies by the longitudinal electric field of an ultrashort transverse magnetic ( TM01 ) optical pulse. The on-axis longitudinal electric field of the pulse is obtained from the free-space divergence equation beyond the so-called slowly-varying-envelope approximation. The instantaneous electron dynamics is studied; numerical simulations predict net energy gains in the GeV range for laser intensities reaching 10(22) W/ cm(2) .

The generation of highly charged Xe(q+) ions up to q=24 is observed in Xe clusters embedded in helium nanodroplets and exposed to intense femtosecond laser pulses (λ=800  nm). Laser intensity resolved measurements show that the high-q ion generation starts at an unexpectedly low threshold intensity of about 10(14)  W/cm2. Above threshold, the Xe ion charge spectrum saturates quickly and changes only weakly for higher laser intensities. Good agreement between these observations and a molecular dynamics analysis allows us to identify the mechanisms responsible for the highly charged ion production and the surprising intensity threshold behavior of the ionization process.