Dependence of the energy of ions accelerated during interaction of the laser pulse obliquelly incident on the thin foil target on the laser polarization is studied experimentally and theoretically. We found that the ion energy being maximal for the p
-polarization gradually decreases when the pulse becomes s-polarized. The experimentally found dependences of the ion energy are explained by invoking the anomalous electron heating which results in high electrostatic potential formation at the target surface. Anomalous heating of electrons beyond the energy of quiver motion in the laser field is described within the framework of theoretical model of driven oscillator with a step-like nonlinearity. We have demonstrated that the electron anomalous heating can be realized in two regimes: nonlinear resonance and stochastic heating, depending on the extent of stochasticity. We have found the accelerated ion energy scaling determined by the laser intensity, pulse duration, polarization angle and incident angle.
A nonlinear oscillator with an abruptly inhomogeneous restoring force driven by an uniform oscillating force exhibits stochastic properties under specific resonance conditions. This behaviour elucidates the elementary mechanism of the electron energi
zation in the strong electromagnetic wave interaction with thin targets.
Coulomb implosion mechanism of the negatively charged ion acceleration in laser plasmas is proposed. When a cluster target is irradiated by an intense laser pulse and the Coulomb explosion of positively charged ions occurs, the negative ions are acce
lerated inward. The maximum energy of negative ions is several times lower than that of positive ions. The theoretical description and Particle-in-Cell simulation of the Coulomb implosion mechanism and the evidence of the negative ion acceleration in the experiments on the high intensity laser pulse interaction with the cluster targets are presented.
