Mechanism for excimer-laser ablation in alkaline-earth metals

The time-of-flight distribution and the amount of desorbed monovalent ion w ere measured for laser ablation of alkaline-earth metals. The experiment is performed using two wavelengths (193-nm ArF excimer laser and 248-nm KrF e xcimer laser), a fluence of less than 500 mJ/cm(2) and an effective pulse d uration of 14-20 ns. Ion desorption occurs at a lower fluence than that pre dicted by a thermal evaporation model. The relationship between the amount of desorbed ion and the fluence shows highly nonlinear behavior. Based on t he obtained results, a model is proposed in which the laser ablation of alk aline-earth metals is caused by the core electron ionization via the multip hoton photochemical process.