Hughes Tyler, Veronis Georgios, Wootton Kent P, Joel England R, Fan Shanhui
Opt Express. 2017 Jun 26;25(13):15414-15427. doi: 10.1364/OE.25.015414.
Dielectric microstructures have generated much interest in recent years as a means of accelerating charged particles when powered by solid state lasers. The acceleration gradient (or particle energy gain per unit length) is an important figure of merit. To design structures with high acceleration gradients, we explore the adjoint variable method, a highly efficient technique used to compute the sensitivity of an objective with respect to a large number of parameters. With this formalism, the sensitivity of the acceleration gradient of a dielectric structure with respect to its entire spatial permittivity distribution is calculated by the use of only two full-field electromagnetic simulations, the original and 'adjoint'. The adjoint simulation corresponds physically to the reciprocal situation of a point charge moving through the accelerator gap and radiating. Using this formalism, we perform numerical optimizations aimed at maximizing acceleration gradients, which generate fabricable structures of greatly improved performance in comparison to previously examined geometries.
近年来，介电微结构作为一种由固态激光器驱动来加速带电粒子的手段引起了广泛关注。加速梯度（或单位长度的粒子能量增益）是一个重要的品质因数。为了设计具有高加速梯度的结构，我们探索了伴随变量法，这是一种用于计算目标函数相对于大量参数的灵敏度的高效技术。通过这种形式体系，仅使用两次全电磁模拟（原始模拟和“伴随”模拟）就可以计算介电结构的加速梯度相对于其整个空间介电常数分布的灵敏度。伴随模拟在物理上对应于点电荷穿过加速器间隙并辐射的相反情况。使用这种形式体系，我们进行了旨在最大化加速梯度的数值优化，与之前研究的几何形状相比，生成了性能有显著改善的可制造结构。
