Evanescent wave is a kind of electromagnetic wave localized on the surface of matter . Evanescent waves exist widely in nature , For example, nanolight sources ( Like quantum dots 、N-V Color center 、 Fluorescent molecules, etc ) The non radiative part of 、 Surface plasmon waves 、 Light waves localized at the interface when total reflection occurs 、 Electromagnetic waves carried by charged particles whose speed is lower than that of light . Evanescent waves can carry a lot of energy and important information , Therefore, it has been deeply studied and discussed in many fields , Such as optical super-resolution imaging and lithography 、 Biosensors 、 Free electron light sources and energy sources . However , Due to the local characteristics of evanescent waves , We always have great difficulties in acquiring and manipulating the energy and information carried by evanescent waves . To address this issue , Northeast University of the United States Liu Yongmin Recently, the professor's research group proposed a new structural design of anisotropic super structure surface , Can effectively radiate evanescent waves into the far field ; meanwhile , The phase and polarization of the radiation field can be accurately controlled by the design of the super structure surface , So that the radiation of evanescent wave can be controlled completely . This work extends the research and application of Hypersurfaces in far-field optics to near-field optics . The first author of the article is Li Lin Doctor , Now he is a researcher of State Key Laboratory of precision spectroscopy science and technology, East China Normal University .

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In this work , Professor Liu's team adopted a strategy based on C Anisotropic hyper structured surfaces of metal nanopore arrays . Excited by evanescent waves ,C Metal nanopores can support both magnetic dipoles in the structural plane and electric dipoles perpendicular to the structural surface . Both of these dipoles can induce far-field electromagnetic radiation , And there is a certain phase difference between the corresponding radiation components . By changing C The opening direction of the hole α, We can change the magnitude of the far-field radiation component induced by magnetic and electric dipoles , And then change the phase of the radiation field . When C Turn one turn in the direction of the opening of the hole (0°-360°), The phase of the radiation field can be realized 0-2π The phase change of . Using this principle , All kinds of evanescent waves can be transformed into far-field radiation , At the same time, the wavefront of the radiation light is controlled integratedly . In this job , Professor Liu's team's research on charged particles Smith-Purcell Radiation is regulated , And through the mechanism of optical total reflection to control Smith-Purcell The radiation is simulated and verified by all optics . They have studied and realized the focusing of the far-field radiation produced by evanescent waves , The validity and accuracy of this new phase control method are proved . meanwhile , The anisotropic surface can also modulate the polarization of the radiation field . The author through the theory 、 Numerical simulation and experiments show that , The polarization state of the radiation field is linearly polarized light , Its polarization direction is related to C The opening direction of the hole is the same , And will follow C The opening direction of the hole is changed by rotation . It's worth pointing out , The method of phase control in this work is different from that of most of the super structured surfaces , It's a new method to control the phase of super structured surface . Previous work on the phase control of super structured surfaces or the geometric phase control of circularly polarized light through the rotation of the same micro nano structure , Or the resonant wavelength can be adjusted by changing the size of the micro nano structure , So as to control the phase of linearly polarized light . This work can adjust the phase of linearly polarized light by the same rotation of micro nano structure , It reduces the requirement of phase control of linearly polarized light for micro nano fabrication . This work provides a new way to extract and explore the near-field energy and information carried by evanescent waves , It has great potential in the research and application of integrated optics . This work will also further stimulate the study of superstructural surfaces and evanescent waves , Including the acquisition and conversion of near-field light energy 、 Integrated free electron light source 、 Near field sensing, etc . Related papers are published online in Laser & Photonics Reviews (DOI: 10.1002/lpor.201900244) On .

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