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Acceleration and distribution of laser-ablated carbon ions near the target surface

The plasma plume induced during laser ablation of graphite is studied both experimentally and theoretically. The hydrodynamic model applied shows that the high velocities of the plume observed in the experiment result from the large pressure gradient built up during laser–plume interaction. This means that at a low laser intensity of ∼109 W cm−2 the acceleration mechanism is rather gasdynamical than electrostatic. The calculated temporal profiles of plasma temperature and electron density in the early phase of expansion are in reasonable agreement with experimental profiles obtained from emission spectroscopy. The effect of evolution of the plasma temperature on time-of-flight signals is presented. It has been shown that the appearance of ions with higher charge prior to ions with lower charge often ascribed to the effect of the induced electric field can be explained by the evolution of the plume temperature.