Unstable longitudinal expansion of plasma foils accelerated by circularly polarized laser pulses in non-transparent regimes

Abstract

Relativistic opaqueness has been considered to be a sufficient condition for the stable compression and acceleration of a negligibly thin plasma foil by a circularly polarized laser pulse. However, in our simulations, we observed that finite-thick plasma foils, which are still relativistically nontransparent to the laser pulse, can be subject to sudden and rapid expansion of the foil even when the pulse intensity is expected to be high enough to suppress the electrostatic Coulomb expansion. Analyzing the distribution of the ponderomotive force over the finite thickness of a slab-like foil, we found a theoretical condition to avoid the new expansion mechanism. Relations between this expansion and the relativistic electron heating and self-induced transparency are discussed.