Blechman Yael, Almeida Euclides, Sain Basudeb, Prior Yehiam
Department of Chemical and Biological Physics , Weizmann Institute of Science , Rehovot 76100 , Israel.
Nano Lett. 2019 Jan 9;19(1):261-268. doi: 10.1021/acs.nanolett.8b03861. Epub 2018 Dec 20.
Controlling the nonlinear optical response of nanoscale metamaterials opens new exciting applications such as frequency conversion or flat metal optical elements. To utilize the already well-developed fabrication methods, a systematic design methodology for obtaining high nonlinearities is required. In this paper we consider an optimization-based approach, combining a multiparameter genetic algorithm with three-dimensional finite-difference time domain (FDTD) simulations. We investigate two choices of the optimization function: one which looks for plasmonic resonance enhancements at the frequencies of the process using linear FDTD, and another one, based on nonlinear FDTD, which directly computes the predicted nonlinear response. We optimize a four-wave-mixing process with specific predefined input frequencies in an array of rectangular nanocavities milled in a thin free-standing gold film. Both approaches yield a significant enhancement of the nonlinear signal. Although the direct calculation gives rise to the maximum possible signal, the linear optimization provides the expected triply resonant configuration with almost the same enhancement, while being much easier to implement in practice.
控制纳米级超材料的非线性光学响应开启了诸如频率转换或平面金属光学元件等令人兴奋的新应用。为了利用已经成熟的制造方法，需要一种用于获得高非线性的系统设计方法。在本文中，我们考虑一种基于优化的方法，将多参数遗传算法与三维时域有限差分（FDTD）模拟相结合。我们研究了两种优化函数的选择：一种是使用线性FDTD在过程频率处寻找等离子体共振增强，另一种基于非线性FDTD，直接计算预测的非线性响应。我们在独立的薄金膜中铣削出的矩形纳米腔阵列中，针对特定的预定义输入频率优化四波混频过程。两种方法都能显著增强非线性信号。虽然直接计算能产生最大可能的信号，但线性优化能提供几乎相同增强效果的预期三重共振配置，同时在实际中更容易实现。
