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Laser & Photonics reviews: driving evanescent waves -- a new type of anisotropic surface

wallpapers News 2020-11-19

evanescent wave is a kind of electromagnetic wave localized on the surface of matter. Evanescent waves exist widely in nature such as the non radiative part of nano light sources (such as quantum dots N-V color centers fluorescent molecules etc.) surface plasmon waves light waves localized at the interface when total reflection occurs electromagnetic waves carried by charged particles whose velocity is lower than that of light etc. Evanescent wave can carry a lot of energy important information so it has been deeply studied discussed in many fields such as optical super-resolution imaging lithography biosensor free electron light source energy. However due to the local characteristics of evanescent waves it is difficult to obtain manipulate the energy information effectively.

In order to solve this problem Professor Liu Yongmin of Northeastern University recently proposed a new anisotropic super structured surface structure design which can effectively radiate evanescent wave to the far field. At the same time the phase polarization of the radiation field can be accurately controlled through the design of super structured surface so that the radiation of evanescent wave can be completely controlled. This work extends the research application of Hypersurfaces in far-field optics to near-field optics. The first author of this paper is Dr. Li Lin a researcher of State Key Laboratory of precision spectroscopy science technology East China Normal University.

in this work Professor Liu's team adopted an anisotropic super structured surface based on a C-shaped metal nanopore array. Under the excitation of evanescent wave the C-shaped metal nanopore can support both the magnetic dipole in the structural plane the electric dipole perpendicular to the structural surface. These two kinds of dipoles can induce far-field electromagnetic radiation there is a certain phase difference between their corresponding radiation components. By changing the opening direction α of the C-shaped hole we can change the size of the far-field radiation component induced by the magnetic dipole the electric dipole then change the phase of the radiation field. When the opening direction of the C-shaped hole is rotated one turn (0 ° - 360 °) the phase of the radiation field can change from 0 to 2 π. Using this principle all kinds of evanescent waves can be transformed into far-field radiation light the wavefront of radiation light can be adjusted controlled in an integrated way. In this work Professor Liu's team controlled the Smith Purcell radiation of charged particles simulated verified the Smith Purcell radiation through the mechanism of optical total reflection. They have studied realized the focusing of far-field radiation generated by evanescent wave which proves the effectiveness accuracy of this new phase control method. At the same time the anisotropic surface can also modulate the polarization of the radiation field. It is proved by theory numerical simulation experiment that the polarization state of the radiation field is linearly polarized light its polarization direction is consistent with the opening direction of the C-shaped hole will change with the rotation of the opening direction of the C-shaped hole. It is worth pointing out that the phase control method in this work is different from that of most of the hyper structured surfaces it is a new phase control method of hyper structured surfaces. Previous work on phase control of super structured surface is to adjust the geometric phase of circularly polarized light by the same rotation of micro nano structure or to adjust the resonant wavelength by changing the size of micro nano structure so as to adjust the phase of linearly polarized light. In this work the phase of linearly polarized light can be adjusted by the same rotation of micro nano structure which reduces the requirement of micro nano processing. This research work provides a new idea for extracting exploring the near-field energy information carried by evanescent waves has great potential in the research application of integrated optics. This work will also further stimulate the research related to superstructural surfaces evanescent waves including the acquisition conversion of near-field light energy integrated free electron light source near-field sensing so on.

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