The interaction of a petawatt laser with a small solid-density plasma bunch is studied by particle-in-cell simulation. It is shown that when irradiated by a laser of intensity $>{10}^{21}\mathrm{W}∕{\mathrm{cm}}^2$, a dense plasma bunch of micrometer size can be efficiently accelerated. The kinetic energy of the ions in the high-density region of the plasma bunch can exceed ten MeV at a density in the ${10}^{23}\text{−}{\mathrm{cm}}^{-3}$ level. Having a flux density orders of magnitude higher than that of the traditional charged-particle pulses, the laser-accelerated plasma bunch can have a wide range of applications. In particular, such a dense energetic plasma bunch impinging on the compressed fuel in inertial fusion can significantly enhance the nuclear-reaction cross section and is thus a promising alternative for fast ignition.

Electron acceleration from the interaction of an intense short-pulse laser with low density plasma is considered. The relation between direct electron acceleration within the laser pulse and that in the wake is investigated analytically. The magnitude and location of the ponderomotive-force-caused charge separation field with respect to that of the pulse determine the relative effectiveness of the two acceleration mechanisms. It is shown that there is an optimum condition for acceleration in the wake. Electron acceleration within the pulse dominates as the pulse becomes sufficiently short, and the latter directly drives and even traps the electrons. The latter can reach ultrahigh energies and can be extracted by impinging the pulse on a solid target.

Dimensional effects in particle-in-cell (PIC) simulation of target normal sheath acceleration (TNSA) of protons are considered. As the spatial divergence of the laser-accelerated hot sheath electrons and the resulting space-charge electric field on the target backside depend on the spatial dimension, the maximum energy of the accelerated protons obtained from three-dimensional (3D) simulations is usually much less than that from two-dimensional (2D) simulations. By closely examining the TNSA of protons in 2D and 3D PIC simulations, we deduce an empirical ratio between the maximum proton energies obtained from the 2D and 3D simulations. This ratio may be useful for estimating the maximum proton energy in realistic (3D) TNSA from the results of the corresponding 2D simulation. It is also shown that the scaling law also applies to TNSA from structured targets.

A simple surface current model is proposed for studying harmonic generation by a short-pulse high-intensity circularly polarized laser irradiating a solid target normally. Exact relativistic electron dynamics is taken into account. It is found that high harmonics peaked at directions normal to that of incidence are efficiently generated.

The scattering of laser light by electrons is considered. When the electron is counterstreaming and highly relativistic, and the laser light ultraintense, the scattered light is mainly in the higher harmonics, and the frequency upshift is further enhanced by the Doppler effect. This provides a mechanism for very large frequency up-conversion.

A simple self-consistent model for the generation of fast electrons during the normal incidence by an ultrashort and ultraintense linearly polarized laser on a solid target is proposed. The electrons are shown to be strongly accelerated in an electron cloud adjacent to the target surface because of resonant interaction with the oscillating component of the ponderomotive force of the laser light.