Vacuum electron acceleration by tightly focused laser pulses with nanoscale targets

Electron acceleration using a tightly focused relativistic short laser pulse interacting with a spherical nanocluster, ultrathin foil or preformed mid-dense plasmas is studied by using three-dimensional particle-in-cell simulations with the Stratton-Chu integrals as the boundary conditions for the incident laser fields. The investigation is performed in the regime where the focal spot size is comparable with the laser wavelength. Generation of high-energy electron multibunch jets with quasimonoenergetic or waterbaglike spectra has been demonstrated. The physical process of acceleration and bunching of the electrons is discussed in detail, as well as particles energy and angular distributions for different laser intensities, focusing optics, target parameters, and laser incidence angles.