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

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-µJ 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.