Plasma-free water droplet shattering by long-wave infrared ultrashort pulses for efficient fog clearing

Abstract

High-power lasers can be used to clear a foggy or cloudy atmosphere by exploding and shattering water microdroplets into smaller fragments. The physics of laser-droplet interaction strongly depend on the excitation wavelength and pulse duration, and new techniques with optimized energy requirements that enable lossless long-distance propagation are urgently needed. In this work, a novel and elegant way of water droplet shattering by sub-mu J long-wave infrared ultrashort laser pulses is proposed, making it possible to practically avoid undesirable electron plasma generation in a water droplet and optical breakdown in air. A multiphysics study is performed, which takes into account a hierarchy of physical processes including free carrier plasma kinetics underpinned by a full-vector nonlinear Maxwell solver and the thermomechanical dynamics of pressure waves followed by droplet shattering into smaller fragments described by Navier-Stokes equations. Our results are crucial both for understanding the fundamental nature of water excitation with long-wave infrared radiation and for development of laser applications such as atmospheric communications. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement.