[en] The interaction of ultraintense, short pulse lasers with a preformed plasma is investigated using particle-in-cell (PIC) computer simulations. For this interaction regime, the electron motion in the presence of the intense light wave is strongly relativistic. Due to the extremely large light pressure associated with such pulses, a deep depression at the critical surface is formed, which causes the absorption to increase as a function of time. The result is that a substantial amount of the laser energy is absorbed by hot electrons that transport into the overdense plasma. There is also a large inward acceleration of ions. Comparison of the present simulation results with data obtained from a current experiment is also presented