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新镜子反射光线的方式与传统镜子不同
诸平
据物理学家组织网(Phys.org)2017年11月14日报道,美国乔治亚理工学院(Georgia Institute of Technology)、美国宾夕法尼亚州立大学(Pennsylvania State University)、美国东北大学( Northeastern University)以及美国赖特-帕特森空军基地(Wright-Patterson Air Force Base)的研究人员合作,设计了一种新型的镜子,此镜子对于光线的反射方式与传统的镜子对光线的反射方式完全不同,新镜子被称为手性变换镜(Chiral Meta-Mirror)。当一个普通镜子反射圆偏振光( circularly polarized light)时,其反射光的自旋状态会发生反转。但是,相比之下,手性变换镜对于圆偏振光的反射则完全不同,反射光保留其自旋状态不变,即反射光的自旋状态与入射圆偏振光是相同的。此手性变换镜在光信息处理、新一代3D电影以及以新的方式来操纵光的其它技术中具有潜在应用价值。此项研究成果是由美国乔治亚理工学院蔡文山(Wenshan Cai音译)领导的研究团队完成的,相关研究结果于2017年10月26日在《纳米快报》(Nano Letters)杂志网站发表——Lei Kang, Sean P. Rodrigues, Mohammad Taghinejad, Shoufeng Lan, Kyu-Tae Lee, Yongmin Liu, Douglas H. Werner, Augustine Urbas, Wenshan Cai. Preserving Spin States upon Reflection: Linear and Nonlinear Responses of a Chiral Meta-Mirror. Nano Lett., 2017, 17: 7102−7109. DOI: 10.1021/acs.nanolett.7b03882
Conventional metallic mirrors flip the spin of a circularly polarized wave upon normal incidence by inverting the direction of the propagation vector. Altering or maintaining the spin state of light waves carrying data is a critical need to be met at the brink of photonic information processing. In this work, we report a chiral metamaterial mirror that strongly absorbs a circularly polarized wave of one spin state and reflects that of the opposite spin in a manner conserving the circular polarization. A circular dichroic response in reflection as large as ~0.5 is experimentally observed in a near-infrared wavelength band. By imaging a fabricated pattern composed of the enantiomeric unit cells, we directly visualize the two key features of our engineered meta-mirrors, namely the chiral-selective absorption and the polarization preservation upon reflection. Beyond the linear regime, the chiral resonances enhance light-matter interaction under circularly polarized excitation, greatly boosting the ability of the metamaterial to perform chiral-selective signal generation and optical imaging in the nonlinear regime. Chiral meta-mirrors, exhibiting giant chiroptical responses and spin-selective near-field enhancement, hold great promise for applications in polarization sensitive electro-optical information processing and biosensing.
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