  In order to realistically simulate the interaction of a femtosecond laser
pulse with a nanometre-thick target it is necessary to consider a target
preplasma formation due to the nanosecond long amplified-spontaneous-emission
pedestal and/or prepulse. The relatively long interaction time dictated that
hydrodynamic simulations should be employed to predict the target particles'
number density distributions prior the arrival of the main laser pulse. By
using the output of the hydrodynamic simulations as input into particle-in-cell
simulations, a detailed understanding of the complete laser-foil interaction is
achieved. Once the laser pulse interacts with the preplasma it deposits a
fraction of its energy on the target, before it is either reflected from the
critical density surface or transmitted through an underdense plasma channel. A
fraction of hot electrons is ejected from the target leaving the foil in a net
positive potential, which in turn results in proton and heavy ion ejection. In
this work protons reaching ~25 MeV are predicted for a laser of ~40 TW peak
power and ~600 MeV are expected from a ~4 PW laser system.
