Couairon A, Kosareva O G, Panov N A, Shipilo D E, Andreeva V A, Jukna V, Nesa F
Opt Express. 2015 Nov 30;23(24):31240-52. doi: 10.1364/OE.23.031240.
Part of the chain in petawatt laser systems may involve extreme focusing conditions for which nonparaxial and vectorial effects have high impact on the propagation of radiation. We investigate the possibility of using propagation equations to simulate numerically the focal spot under these conditions. We derive a unidirectional propagation equation for the Hertz vector, describing linear and nonlinear propagation under situations where nonparaxial diffraction and vectorial effects become significant. By comparing our simulations to the results of vector diffraction integrals in the case of linear tight-focusing by a parabolic mirror, we establish a practical criterion for the critical f -number below which initializing a propagation equation with a parabolic input phase becomes inaccurate. We propose a method to find suitable input conditions for propagation equations beyond this limit. Extreme focusing conditions are shown to be modeled accurately by means of numerical simulations of the unidirectional Hertz-vector propagation equation initialized with suitable input conditions.
拍瓦激光系统中的部分光路可能涉及极端聚焦条件，在这种条件下，非傍轴和矢量效应会对辐射传播产生重大影响。我们研究了使用传播方程对这些条件下的焦点光斑进行数值模拟的可能性。我们推导了赫兹矢量的单向传播方程，用于描述在非傍轴衍射和矢量效应变得显著的情况下的线性和非线性传播。通过将我们的模拟结果与抛物面镜线性紧聚焦情况下的矢量衍射积分结果进行比较，我们建立了一个临界f数的实用准则，低于该准则时，用抛物面输入相位初始化传播方程会变得不准确。我们提出了一种方法来找到超出此限制的传播方程的合适输入条件。结果表明，通过使用合适输入条件初始化的单向赫兹矢量传播方程进行数值模拟，可以准确地对极端聚焦条件进行建模。
