相对论性自聚焦对超强激光束在等离子体中传输特性的影响
摘要：随着激光技术的迅速发展，激光束的峰值强度越来越高（如 ）。当如此高强度激光作用在等离子体中时，等离子体中的电子在激光场有质动力作用下沿横向被排开形成密度通道，其在激光电场直接加速下的抖动速度非常接近真空中的光速，引起电子质量强烈的相对论性增加，从而进1步使得激光束聚焦，即相对论性自聚焦效应。1般地，对该问题常采用弱相对论近似进行研究。为突破该近似的局限性，本文利用Hamilton-Jacobi方法对强激光在等离子体介质中的相对论性自聚焦效应进行研究，得出光束半径随传输距离演化的包络方程。计算结果表明，激光束在等离子体介质中的自聚焦特性同时与激光功率和初时光强有关，在本文所采用的传输模型下，即使激光功率超过弱相对论近似下得出的自聚焦临界功率，也不会出现束宽聚焦为0而光强为无穷大的非物理情景。相反地，会出现光束随传输距离散焦或聚焦振荡变化甚至形成空间孤子解。
关键词：等离子体，超强激光束，相对论自聚焦，传输特性
Relativistic self-focusing of ultra-intense laser beams propagating in plasmas
Abstract: Laser intensity increases dramatically with the development of laser technique, e.g., . When such high intense laser beam interacts with plasma, electrons are expelled transversely from the axis forming a plasma channel and their (quiver) velocity accelerated by laser electric field approximates to that of light in vacuum, which increases the mass of electrons and then focuses the beam (the effect of relativistic self-focusing). Usually, the weakly relativistic limit is used to analyze this effect and leads to non-physical pictures such as beam spot size is zero. Making use of the Hamilton-Jacobi equation, we study the effect of relativistic self-focusing when an ultra-intense laser beam is propagating in plasma. An envelope equation govern the evolution of beam spot size along the propagation distance is obtained and is suitable to intense as well as ultra-intense cases. Beam propagation properties are showed to be governed by beam power and initial peak intensity, and there are no non-physical pictures even the power exceeds the critical relativistic self-focusing evaluated in the weakly relativistic limit. On the contrary, beam spot size experiences defocusing or focusing oscillations even forms spatial solution along the propagation distance.
Key words: plasma；ultra-intense laser beam；relativistic self-focusing；Propagation properties
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