A Super Lens System for Demagnification Imaging Beyond the Diffraction Limit
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A Super Lens System for Demagnification Imaging Beyond the Diffraction Limit Jianjie Dong & Juan Liu & Xingxing Zhao & Peng Liu & Jing Liu & Guoguo Kang & Jinghui Xie & Yongtian Wang
Received: 7 February 2013 / Accepted: 30 April 2013 # Springer Science+Business Media New York 2013
Abstract A super lens system is proposed to achieve subdiffraction limit demagnification imaging. The super lens system consists of a hyperlens with planar input and output surfaces, a metal superlens, and a plasmonic reflector. By employing the hyperlens to transform evanescent waves into propagating waves and employing the metal superlens and the plasmonic reflector to amplify evanescent waves, the super lens system can produce a subdiffraction limit image with relatively high electric field intensity. The reduction factor of the super lens system depends on the geometric parameters of the hyperlens. Simulation results show that an image with a half-pitch resolution of about one tenth the operating wavelength and a reduction factor of about 2.2 can be produced by the super lens system. The proposed super lens system has potential applications in nanolithography. Keywords Subwavelength optical imaging . Surface plasmon . Superlens
Introduction It is well known that the resolution of conventional lenses is limited by the diffraction of light because the evanescent waves which carry subwavelength information about the object decay exponentially with distance and thus have a negligible contribution to images. To achieve a resolution below the diffraction limit, some unconventional lenses, such as the perfect lens [1], the metal superlens [1, 2], and the hyperlens [3], have been proposed. The perfect lens, a slab of negative refractive index material, can produce a perfect image of a J. Dong : J. Liu (*) : X. Zhao : P. Liu : J. Liu : G. Kang : J. Xie : Y. Wang School of Optoelectronics, Beijing Institute of Technology, Beijing 100081, China e-mail: [email protected]
subdiffraction limit object [1], but it suffers from the fact that all materials found in nature have a positive refractive index. The metal superlens, a slab of metal, can amplify evanescent waves of the object light by the excitation of surface plasmon polaritons and thus can produce an image of a subdiffraction limit object [2, 4–7]. Metal superlenses have been successfully used in nanolithography [8–13]. The photolithography technique using metal superlenses, called superlens lithography, can overcome the diffraction limit. However, for lithography applications, the fabrication of the mask becomes difficult when we use metal superlenses to produce higher-resolution images because the object and its image produced by metal superlenses have the same resolution. The demagnification imaging can effectively overcome this difficulty and the hyperlens has such an imaging function. The hyperlens consists of a stack of alternating metal and dielectric layers and has a hyperbolic dispersion relation. Inside the hyperlens, the waves which have very large spatial frequency are stil
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