单轴晶体中产生的高纯度纵向针形磁化场

High-purity longitudinal needle-shaped magnetization fields produced in uniaxial crystals

基于理查德-沃尔夫矢量衍射理论和逆法拉第效应,提出一种在单轴晶体中产生高纯度纵向针形磁化场的方法.该方法通过电偶极子对数N及其阵列多参数调控,利用单轴晶体中的电偶极子反向辐射构建出优化的入瞳光场,再正向紧聚焦获得所需目标磁化场.模拟结果表明:当N=1时,单轴晶体中产生的磁化场比在同性介质中焦深长度增加近1.4倍,横向分辨率提高5%.当N=2和N=3时,单轴晶体中获得的纵向针形磁化场随着电偶极子对数增加,轴向焦深增加了10%,横向分辨率提高了18%.随着磁化场轮廓表面值从0.1变化到1,针形磁化场的纯度逐渐增大到1.尤其当N=2、轮廓表面值为0.1时,磁化场纯度高达95%.研究结果为在各向异性介质中生成更高纯度、针长更长的纵向磁化场提供了可行性方案,也为全光磁记录、原子捕获和光刻等实际应用中入瞳光场的优化选取提供了理论指导.

Based on the Richard-Wolf vector diffraction theory and the inverse Faraday effect, a method of generating a high-purity longitudinal needle-shaped magnetization field in the uniaxial crystal is proposed. In this method,the inverse radiation of the electric dipole in the uniaxial crystal is used to construct an optimal entry pupil light field through regulating the multi-parameter of the number of electric dipole pairs N and their array, and then the magnetization field of the desired target is obtained by forward tightly focusing. The simulation results show that when N = 1, the focal length of the magnetic field generated in the uniaxial crystal increases by 1.4times and the lateral resolution increases by 5% compared with the counterparts in an isotropic medium. It can be further seen that when N = 2 and N = 3, with the increase of the number of electric dipole pairs, the focal length of the needle magnetic field generated in the uniaxial crystal increases by 10%, and the lateral resolution increases by 18%. The purity of the needle magnetic field gradually increases to 1 as the magnetization field profile surface value changes from 0.1 to 1. Especially when N = 2 and the contour surface value is 0.1, the magnetic field purity is as high as 95%. The results provide a feasible scheme for generating a longitudinal magnetization field with higher purity and longer focal length in an anisotropic medium, and also present the theoretical guidance for selecting optimal pupil beams in practical applications such as all-optical magnetic recording, atom capture and lithography.