The hydrodynamic efficiency of laser-target acceleration

The acceleration of a thin foil using a laser pulse is studied. It is shown that the acceleration efficiency eta H is heavily dependent on the behaviour of the corona ejected by the foil: there is no universal relation eta H ( Delta M/M 0 ),M 0 and Delta M being initial foil mass and ablated mass, respectively. Known results on the coronal flow are used to check the theory against experimental data available in the literature; effects due to both a non-planar corona, and the time-dependence of the laser irradiance, are considered. The agreement with experiments is substantially better than that for previous analyses. Acceleration of thin spherical shells is also discussed.