Modulation of Main Lobe for Superfocusing Using Subwavelength Metallic Heterostructures
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A subwavelength metallic heterostructure is put forth for the purpose of suppressing sidelobes and improving superfocusing at a quasi-far field region. Improvement has been made by means of optimization of the heterostructure composed of structured Au and Ag thin films. By tuning thicknesses of both the structured Au and Ag films, we can modulate propagation distance of the plasmonic lens and beam width of main lobe for the superfocusing. A finite-difference and time-domain (FDTD) algorithm-based computational numerical calculation was carried out for analyzing the focusing performance and tuning ability of the metal films. Our computational calculation results show that the sidelobes which play negative role for the focusing can be suppressed significantly in the case of the metal film thicknesses of h Au = 50 nm and h Ag = 10 nm. Theoretically, the metallic structure with smaller thicknesses of the structured Au and Ag films is helpful for improving the focusing performance. This heterostructure-based device is possible to be used as a superlens or nanoprobe in data storage, nanometrology/inspection, and biosensing etc.
KeywordsHeterostructure Superfocusing FDTD Main lobe Sidelobes
The work was supported by the National Natural Science Foundation of China (No.60877021) and “Distinguished Talent Program” from University of Electronic Science and Technology of China (No. 08JC00401). The authors acknowledge the financial support from A*STAR (Agency for Science, Technology and Research), Singapore, through the project on “Novel optical nanoprobe for nanometrology based on surface plasmon polaritons” (SERC Grant No. 072 101 0023).
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