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带金属尖四棱锥小孔光探针光斑近场分布数值模拟
Numerical simulation of the near-field distribution of light spot of aperture pyramid-type optical probe with a metal tip
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摘要: 采用时域有限差分法(FDTD)研究了带金属尖四棱锥小孔光探针光斑近场分布特性,分析了金属尖的长度、尖端半径及距离小孔位置等因素对近场电场分布的影响.讨论了该类光探针的电磁波通过等离子体激元方式从小孔传输到金属尖的机理.Taminiau等人用不同方法获得的计算结果在本文的计算结果中得到了印证.在此基础上,本文重点分析、讨论了Pohl等人在1984-1986年获得20-25 nm高分辨率图像的原由,讨论了该实验系统的成像机理和类型的归属.计算结果表明:Pohl等人的实验系统成像机理已离开小孔径扫描近场光学显微镜类型,报告认为应归属金属尖散射扫描近场光学显微镜一类.本结果对设计性能优良的光探针具有参考意义.Abstract: The finite-difference time-domain method (FDTD) is employed to investigate the near-field distribution of the light spot of aperture pyramld-type optical probe with a metal tip. The factors that have some influence on the electric field distribution such as the length, radius and position departed from aperture of the tip are investigated. The mechanism of electromngnetic wave transmitting from the aperture to metal tip by way of plasmon is discussed. Our calculation results are consistent with the results obtained by Taminian with different methods. How and why Pohl etc. have obtained images with high resolution in the 20——25 nm range between 1984 and 1986 are analyzed. The imaging mechanism of their experiment system is discussed. Numerical simulation demonstrates that the imaging mechanism of Pohl's experiment system may belong to a scattering-type near-field optical microscope (S-SNOM) rather than an aperture scanning near-field optical microscope (A-SNOM). This paper can help us to find optimized tip design in the future.
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