Near-threshold ablation of target material irradiated with pulsed ion beams

The process of target ablation induced by pulsed ion beams is investigated. The beam power density of 0.01-0.1 GW/cm2 is around the sublimation energy of the target material. The thickness of the layer to be removed from the target is estimated from the temperature distribution calculated numerically with a diffusion equation. The emitted particles are collected with C collectors, which are later subjected to RBS and SEM/EPMA analyses. It is found that ablated particles forming a film on the collector amount to only 10% of the target atoms within the maximum range of the ions, while a significant amount of the ablated material is observed as macroscopic particles with equivalent diameters up to several tens of micrometers. TOF measurements of the ablation plume together with RBS measurements of thin-film targets after irradiation suggest that the formation of the film is predominated by vaporization from the surface of the ablated mass, which is recondensed on the collector before completing the vaporization. (Author)