紧聚焦角向偏振分数阶涡旋光诱导磁化场特性  

Investigation on magnetization induced by tightly focused azimuthally polarized fractional vortex beam

作　　者：曹重阳 陆健能 张恒闻 朱竹青[1] 王晓雷[2] 顾兵[3,4] Cao Chong-Yang;Lu Jian-Neng;Zhang Heng-Wen;Zhu Zhu-Qing;Wang Xiao-Lei;Gu Bing(Key Laboratory of Optoelectronics Technology of Jiangsu Province,School of Physics and Technology,Nanjing Normal University,Nanjing 210023,China;Institute of Modern Optics,College of Electronic Information and Optical Engineering,Nankai University,Tianjin 300350,China;Advanced Photonics Center,Southeast University,Nanjing 210096,China;Collaborative Innovation Center of Light Manipulations and Applications,Shandong Normal University,Jinan 250358,China)

机构地区：[1]南京师范大学物理科学与技术学院,江苏省光电子技术重点实验室,南京210023 [2]南开大学电子信息与光学工程学院,现代光学研究所,天津300350 [3]东南大学,先进光子学中心,南京210096 [4]山东师范大学光场调控与应用协同创新中心,济南250358

出　　处：《物理学报》2020年第16期229-236,共8页Acta Physica Sinica

基　　金：国家自然科学基金(批准号:11774055,61875093);江苏省自然科学基金(批准号:BK20181384);天津市自然科学基金(批准号:19JCYBJC16500)资助的课题。

摘　　要：基于理查德-沃尔夫矢量衍射理论和逆法拉第效应,首次推导出紧聚焦角向偏振分数阶涡旋光诱导磁化场表达式,分析出角向偏振分数阶涡旋光诱导磁化场可近似等效为有限个相邻整数阶涡旋角向偏振光诱导磁化场与其交叉诱导磁化场的加权叠加.数值模拟了紧聚焦条件下不同分数阶涡旋角向偏振光诱导磁化场的分布特性.模拟结果表明角向偏振分数阶涡旋光诱导磁化场呈非对称分布.当取分数阶涡旋拓扑荷α∈[0.5,1.5]时,随着涡旋拓扑荷的增加,磁化场横向平面分布出现分裂现象,同时还引起磁斑垂直于光轴方向的自移效应.当α=0.5或1.5时,磁斑中心最大偏移量达0.24λ;当分数阶涡旋拓扑荷α∈(2,3]时,磁化场横向平面分布分裂出2个强度热点,强度分布环径逐渐变大.当分数阶涡旋拓扑荷趋于α=3整数时,磁化场横向平面分布也趋于圆对称性分布.特别有趣的是,当分数阶涡旋拓扑荷取半整数,尤其大于3时,磁化场强度热点数与其包围的暗点数均与涡旋阶数存在正相关关系,其中热点数为α-0.5,暗点数为α-1.5.这些研究结果将可应用于全光磁记录和磁性粒子的捕获与操控等.All-optical magnetic recording based on the inverse Faraday effect has become a research hotspot in recent years due to its ultra-high storage density and ultra-fast magnetization reversal rate. Existing studies have shown that by optimizing the phase modulation or performing 4π tight focusing of azimuthally polarized vortex beams, high-resolution longitudinal magnetization fields with different axisymmetric intensity patterns can be generated. In order to meet the requirements of more complex all-optical magnetic recording and asymmetric magnetic particle capture and manipulation, it is particularly important to generate an asymmetric lightinduced magnetization field with adjustable center position. Studies have shown that the fractional vortex phase could lead to the asymmetric focal field distribution generation under tight focusing conditions, which means that the tightly-focused azimuthally polarized light carrying the fractional vortex phase can produce a novel asymmetric light-induced magnetization field. As a new degree of freedom for the regulation of the magnetization field, the fractional topological charge will bring more new phenomena, new effects and new applications in the field of interaction between light and matter. In this work, for the first time to our knowledge, the magnetization induced by tightly focused azimuthally polarized fractional vortex beam is studied based on the Richard-Wolf vector diffraction theory and the inverse Faraday effect. The equivalent approximation of the magnetization induced by azimuthally polarized fractional vortex beam regarded as a weighted superposition of magnetization induced and crossly induced by a finite number of azimuthally polarized adjacent integer-order vortex beams, where the number of the equivalent terms is chosen by using the histogram intersection method of the intensity distribution image of the magnetization field. The magnetization field distribution under different values of a are also numerically simulated. Studies have shown that magnetiza

关 键 词：非对称分布 分数阶涡旋 逆法拉第效应 紧聚焦 

分 类 号：O437[机械工程—光学工程]