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.

中文翻译：

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长波红外超短脉冲使无等离子体的水滴破碎，有效清除雾气

大功率激光可以通过将水微滴爆炸并粉碎成更小的碎片来清除有雾或多云的气氛。激光与液滴相互作用的物理特性在很大程度上取决于激发波长和脉冲持续时间，因此迫切需要具有优化能量需求的新技术，以实现无损长距离传播。在这项工作中，提出了一种通过亚µJ长波红外超短激光脉冲粉碎水滴的新颖而优雅的方法，从而可以切实避免水滴中电子等离子体的产生和空气中的光学击穿。进行了多物理场研究，它考虑了物理过程的层次结构，包括全矢量非线性Maxwell求解器所支持的自由载流子等离子体动力学以及压力波的热力学动力学，随后液滴被粉碎成Navier-Stokes方程所描述的较小碎片。我们的结果对于理解长波红外辐射激发水的基本性质以及开发激光应用（例如大气通信）都至关重要。