Laser Ablation of Alkaline Earth Metals Investigated by Time-of-Flight Mass Spectroscopy: Ion Desorption by Core-Electron Excitation

The time-of-flight distribution and the amount of desorbed monovalent ions have been measured in the laser ablation of alkaline earth metals. The obtained relationship between the amount of ions and the laser fluence indicates that the desorption is caused by 5-, 4- and 3-photon processes for Ca, Sr and Ba, respectively when an ArF excimer laser is used as a light source. On the basis of the results, a model is proposed in which the laser ablation of the alkaline earth metals is triggered by excitation of the core electrons at the highest energy level.