The effect of phase front deformation on the growth of the filamentation instability in laser–plasma interactions

Laser pulses of 0.9 kJ/1 ns/1053 nm were focused onto low-Z plastic targets in both spherical and planar geometry. The uniformity of the resulting plasma production was studied using x-ray pinhole imaging. Evidence is provided suggesting that thermal filamentation starts to occur for irradiances on the target of I lambda(2) >= 10(14) W cm(-2) mu m(2), even on deployment of phase plates to improve the focal spot spatial uniformity. The experiments are supported by both analytical modelling and two-dimensional particle-in-cell simulations. The implications for the applications of laser-plasma interactions that require high degrees of uniform irradiation are discussed.