EXCIMER-LASER INDUCED THERMAL EVAPORATION AND ABLATION OF SILICON-CARBIDE

It is well known that the ablation of material from a solid target exh ibits a threshold behaviour. The ablation of material is usually perfo rmed at later fluences significantly above the threshold and considera bly high ablation rates are achieved. No particular effort has been de voted to the study of the low energy range, near the ablation threshol d. This regime is of particular interest in what it might give insight on the reason for the presence of a threshold and then on the physica l processes underlying the ablation itself. We have measured the ablat ion rate of silicon carbide single crystal targets induced by XeCl las er pulses as function of the laser fluence over a wide range, from bel ow to well above the threshold. We have investigated the angular distr ibution of the emitted material through the measurements of the thickn ess of the deposited films; also, the morphology of the craters left i n the irradiated targets as a function of the laser fluence has been m onitored. We have modelled the surface heating and melting due to the absorption of the laser light, and calculated the surface temperature as function of time by using the well known ''thermal model'' often us ed for the laser annealing. Thermal evaporation from the liquid surfac e can then be calculated for each laser pulse energy and compared to t he observed ablation rates.