Laser-induced plasma formation during pulsed laser deposition

Abstract

The ablation of Al₂O₃ by CO₂ laser radiation is investigated both theoretically and experimentally. The model connects the laser-induced phase transition from condensed to vaporized state of the target and the dynamic of the emerging process plasma. The plasma is described in a two-fluid approximation by use of non-dissipative gas-dynamical equations incorporating absorption of laser radiation in the plasma and the dynamic of its ionization state. In the experimental part, the geometry of the luminous process plasma above the target at different instances is detected and the weight loss of the target as a function of the fluence is measured. At an Ar-base pressure below 1 mbar, both calculated and measured results reveal that there exist two zones in the process plasma: one which is directly attached to the target surface throughout the whole process, and another which is recognized as an outward moving shock front. Further, it is seen from both approaches that, due to absorption of laser radiation by the plasma, the weight loss has a local maximum.