HYDRODYNAMICS OF LASER EROSIVE JET GENERATING NANOSCALE PARTICLES

A 2D-hydrodynamical model is developed for simulation of ultrafine par ticle elaboration by means of the laser-evaporation technique. The gen eral picture of the process can be predicted as follows, An erosive fl ow of the submerged jet type is formed under laser evaporation of a ta r et material into ambient gas atmosphere. Due to the interaction with surrounding gas, the erosive flow is cooled and the vapour condenses generating nanoscale particles. A thin condensation front is formed be tween the erosive vapour-gas jet and cold ambient inert gas. The gas f low streamlines intersect the condensation surface twice and according ly the condensation process is divided into two stages. The initial st age corresponds to the inlet part of the front near the laser irradiat ion spot, where streamlines are directed inward the erosive jet, homog eneous nucleation and condensational growth of nucleation centres take place here. The formed particles of a condensate are transferred by t he inert gas into internal flow area, where the condensation is suspen ded. At the final stage, the particles intersect the condensation fron t from within the vapour-gas mixture at an outlet section where they c ontinue to grow. The resulting particle size distribution depends both on ambient gas pressure and laser irradiation conditions.