The interaction of a high‐power proton beam with 10‐ to 75‐&mgr;m‐thick double layered aluminum targets has been investigated. The experiments were carried out at the Karlsruhe Light Ion Facility using laser Doppler velocimetry with subnanosecond temporal resolution. The results allow us to determine with high accuracy the range of 1.53 MeV protons in the hot aluminum ablation plasma and to reveal the contribution of the thermal conductivity to the state of the target. An analytical model based on an acoustic approximation was established to interpret the ablative acceleration of the target foils during the whole rise time of the accelerator voltage until the maximum ion range is reached. From this model follows that a shock wave is induced into the adjacent material only when the expansion velocity of the ablation zone exactly equals the sound velocity in the target. ©1996 American Institute of Physics.