Hydrodynamics of laser erosive jet generating nanoscale particles

Abstract

A 2D-hydrodynamical model is developed for simulation of ultrafine particle elaboration by means of the laser-evaporation technique. The general picture of the process can be predicted as follows. An erosive flow of the submerged jet type is formed under laser evaporation of a target 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 between the erosive vapour–gas jet and cold ambient inert gas. The gas flow streamlines intersect the condensation surface twice and accordingly the condensation process is divided into two stages. The initial stage corresponds to the inlet part of the front near the laser irradiation spot, where streamlines are directed inward the erosive jet, homogeneous nucleation and condensational growth of nucleation centres take place here. The formed particles of a condensate are transferred by the inert gas into internal flow area, where the condensation is suspended. At the final stage, the particles intersect the condensation front from within the vapour–gas mixture at an outlet section where they continue to grow. The resulting particle size distribution depends both on ambient gas pressure and laser irradiation conditions.