Numerical simulation of optical breakdown in a liquid droplet induced by a laser pulse

Abstract

Modelling and simulation of interaction of laser pulse with individual liquid droplets are of crucial importance in terms of development and code coupling for simulation of laser propulsion and detonation in gas-droplet systems. These applications are challenging and complex for many reasons, one among them is the disparate time and length scales that are required to resolve for an accurate physical representation of the problem. The injection of liquid droplets with low evaporation temperature causes optical breakdown on the individual droplet and leads to a drop of the minimum pulse energy of detonation in the gas-droplet mixture. The mathematical models of various stages of the optical breakdown on individual droplet and numerical methodology for computer modelling of the laser-induced breakdown are developed. Sub-models of optical breakdown on liquid droplet include droplet heating to boiling temperature, its evaporation and formation of vapor aureole around the droplet, ionization of vapor aureole and development of electron avalanche, appearance of micro-plasma spots and their expansion, propagation of shock wave inside the droplet and in the surrounding gas. The threshold intensity of optical breakdown on individual water droplet and its dependence on droplet radius, location of droplet, total energy and radius of laser pulse are studied.