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In order to improve the resolution of terahertz near-field microscopic imaging technology, an ultra-thin thickness-graded silver-plated strip probe with the same duty cycle is designed to realize the excitation of spoof surface plasmons. By comparing with two other probes with different structures, it can be found that the thickness-graded silver-plated strip probe can produce a strong electric field enhancement effect. Thereafter, the influence of the polarization direction of the incident electric field and the number of periodic metal stripes on the electric field which are generated at the tip of the probe is investigated. It is found that this case is highly consistent with the electric field distribution in Richards-Wolf vector diffraction theory when the incident light is linearly polarized. The electric field intensity generated at the tip of the thickness-graded silver-plated strip probe can be flexibly and effectively manipulated by changing the polarization direction of the incident electric field. When the number of thickness-graded silver-plated strips is 12, the minimum size of the focal spot is 20 μm, which is λ/150. When the number of thickness-graded silver-plated strips is 4, the electric field intensity enhancement factor at the focal spot is 849. The electric field intensity enhancement factor at the focal spot increases continuously as the number of periodic metal stripes increases, and the size of focal spot decreases continuously as the number of periodic metal stripes decreases. This result shows that the tight focusing and electric field enhancement of terahertz waves can be achieved by using an ultra-thin thickness-graded silver-plated strip probe. The research results in this paper have important guiding significance for manipulating the electric field in the terahertz band.
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Keywords:
- terahertz /
- spoof surface plasmons /
- super-resolution /
- optical field manipulation
[1] Tormo A D, Khalenkow D, Saurav K, Skirtach A G, Thomas N L 2017 Opt. Lett. 42 4410
Google Scholar
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Google Scholar
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[18] Mbonye M, Mendis R, Mittleman D M 2012 Appl. Phys. Lett. 100 111120
Google Scholar
[19] Schnell M, Alonso-González P, Arzubiaga L, Casanova F, Hueso L E, Chuvilin A, Hillenbrand R 2011 Nat. Photon. 5 283
Google Scholar
[20] 黄铁军, 汤恒河, 谭云华, 刘濮鲲 2017全国微波毫米波会议论文集 (上册) 中国杭州, 2017年5月8日 第268页
Huang T J, Tang H H, Tan Y H, Liu P K 2017 Proceedings of the National Conference on Microwave Millimeter Wave (Vol. I) Hangzhou, China, May 8, 2017 p268 (in Chinese)
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Tang H H, Huang T J, Liu P K 2018 Proceedings of the National Conference on Microwave Millimeter Wave (Vol. II) Chengdu, China, May 6, 2018 p77 (in Chinese)
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图 1 厚度渐变镀银条带探针及不同平面处尖端结构放大示意图
Fig. 1. Thickness gradient silver plated strip probe schematic and the magnified schematic diagram of the structure at the tip in the different planes.
图 2 三种探针的结构和y-z平面光场分布 (a) Teflon探针结构; (b) y-z平面Teflon探针的光场分布; (c) 尖端全镀银探针结构; (d) y-z平面尖端全镀银探针的光场分布; (e) 厚度渐变镀银条带探针结构; (f) y-z平面厚度渐变镀银条带探针的光场分布
Fig. 2. Structure of the three probes and light field distribution in the y-z plane: (a) A Teflon probe structure; (b) light field distribution of a Teflon probe in the y-z plane; (c) a fully silver-plated probe structure; (d) light field distribution at the tip of a fully silver-plated probe in the y-z plane; (e) a thickness-graded silver-plated strip probe structure; (f) light field distribution of a thickness-graded silver-plated strip probe in the y-z plane.
图 3 y-z平面沿探针中心线 (y = 0)的尖端电场强度分布及归一化电场强度分布曲线 (a)厚度渐变镀银条带探针尖端光场分布; (b) 归一化电场强度分布
Fig. 3. Peak electric field intensity distribution and normalized electric field intensity distribution curve along the probe centerline (y = 0) in the y-z plane: (a) The light field distribution at the tip of a thickness-graded silver-plated strip probe; (b) the normalized electric field intensity distribution curve.
图 4 x-y平面三种探针电场强度分布
Fig. 4. Distribution of electric field intensity of three kinds of probes in x-y plane.
图 5 不同偏振的太赫兹波在厚度渐变镀银条带探针尖端处产生的x-y平面的电场强度分布 第一行到第四行分别为入射波沿y轴偏振、x轴偏振、左旋圆偏振、右旋圆偏振的紧聚焦电场强度分布; 第一列到第四列分别为紧聚焦电场的Ex分量、Ey分量、Ez分量和Etotal总场
Fig. 5. The electric field strength at the tip of the thickness-graded silver-plated strip probe is distributed in the x-y plane when the polarization directions of the incident terahertz waves are different. The first row to the fourth row are the tightly focused electric field intensity distributions of the incident wave along the y-axis polarization, the x-axis polarization, the left-hand circular polarization, and the right-hand circular polarization. The first to fourth columns are the Ex component, Ey component, Ez component, and Etotal of the tightly focused electric field, respectively.
图 6 不同θ值对应的厚度渐变镀银条带探针结构的表面电流和紧聚焦光场的电场强度曲线 第一行到第四行分别为θ = 30°, 45°, 60°和90°的情况; 第一列到第三列分别为x-y平面的探针结构、表面电流分布、紧聚焦光场归一化电场强度
Fig. 6. Surface current and tightly focused electric field intensity curves of the thickness-graded silver-plated strip probe structure corresponding to different θ values. The first to fourth rows are the cases of θ = 30°, 45°, 60°, and 90°, respectively. The first to third columns are the probe structure, the surface current distribution, and the normalized electric field intensity of tightly focused light field in the x-y plane, respectively.
表 1 不同θ值所对应的Emax/E0和FWHM
Table 1. Emax/E0 and FWHM corresponding to different θ values.
θ 30º 45º 60º 90º Emax/E0 672.6 744.7 768 849 FWHM λ/150 (20 μm) λ/125 (24 μm) λ/115 (26 μm) λ/100 (30 μm) 
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[1] Tormo A D, Khalenkow D, Saurav K, Skirtach A G, Thomas N L 2017 Opt. Lett. 42 4410
Google Scholar
[2] Degl’Innocenti R, Wallis R, Wei B B, Xiao L, Kindness S J, Mitrofanov O, Weimer P B, Hofmann S, Beere H E, Ritchie D A 2017 ACS Photonics 4 2150
Google Scholar
[3] Liu J B, Mendis R, Mittleman D M, Sakoda N 2013 Appl. Phys. Lett. 103 031104
[4] Moon K, Park H, Kim J, Do Y, Lee S, Lee G, Kang H, Han H 2015 Nano Lett. 15 549
[5] Maier S A, Andrews S R, Martin-Moreno L, Garcia-Vidal F J 2006 Phys. Rev. Lett. 97 176805
Google Scholar
[6] Tang H H, Liu P K 2015 Opt. Lett. 40 5822
[7] Shen X P, Cui T J, Martin-Cano Diego, Garcia-Vidal F J 2013 Proceedings of the National Academy of Sciences of the United States of America 110 1
Google Scholar
[8] Pendry J B, Martín-Moreno L, Garcia-Vidal F J 2004 Science 305 5685
[9] Fernández-Domínguez A I, Martín-Moreno L, García-Vidal F J, Andrews S R, Maier S A 2008 IEEE J. Sel. Top. Quant. 14 6
Google Scholar
[10] Brock E M G, Hendry E, Hibbins A P 2011 Appl. Phys. Lett. 99 051108
[11] Zhao W S, Eldaiki O M, Yang R X, Lu Z L 2010 Opt. Express 18 20
[12] Liu L L,Li Z, Gu C Q, Ning P P, Xu B Z, Niu Z Y, Zhao Y J 2014 J. Appl. Phys. 116 013501
Google Scholar
[13] Li Z, Liu L L, Xu B Z, Ning P P, Chen C, Xu J, Chen X L, Gu C Q, Ning Q 2016 Sci. Rep. 6 21199
Google Scholar
[14] Li Z, Xu B Z, Liu L L, Xu J, Chen C, Gu C Q, Zhou Y J 2016 Sci. Rep. 6 27158
Google Scholar
[15] Barnes W L, Dereux A, Ebbesen T W 2003 Nature 824 6950
[16] Li Z, Xu J, Chen C, Sun Y H,Xu B Z, Liu L L, Gu C Q 2016 Appl. Opt. 55 36
Google Scholar
[17] Xu J, Li Z, Liu L L, Chen C, Xu B Z, Ning P P, Gu C Q 2016 Opt. Commun. 372 155
Google Scholar
[18] Mbonye M, Mendis R, Mittleman D M 2012 Appl. Phys. Lett. 100 111120
Google Scholar
[19] Schnell M, Alonso-González P, Arzubiaga L, Casanova F, Hueso L E, Chuvilin A, Hillenbrand R 2011 Nat. Photon. 5 283
Google Scholar
[20] 黄铁军, 汤恒河, 谭云华, 刘濮鲲 2017全国微波毫米波会议论文集 (上册) 中国杭州, 2017年5月8日 第268页
Huang T J, Tang H H, Tan Y H, Liu P K 2017 Proceedings of the National Conference on Microwave Millimeter Wave (Vol. I) Hangzhou, China, May 8, 2017 p268 (in Chinese)
[21] 汤恒河, 黄铁军, 刘濮鲲 2018 全国微波毫米波会议论文集 (下册) 中国成都, 2018年5月6日 第77页
Tang H H, Huang T J, Liu P K 2018 Proceedings of the National Conference on Microwave Millimeter Wave (Vol. II) Chengdu, China, May 6, 2018 p77 (in Chinese)
[22] Huang T J, Tang H H, Yin L Z, Liu J Y, Tan Y H, Liu P K 2018 Opt. Lett. 43 15
[23] Dorn R, Quabis S, Leuchs G 2003 Phys. Rev. Lett. 91 233901
[24] Wang T T, Kuang C F, Hao X, Liu X 2013 Optik 124 21
[25] Youngworth K S, Brown T G 2000 Opt. Express 7 2
Google Scholar
[26] Quabis S, Dorn R, Eberler M, Glöckl O, Leuchs G 2000 Opt. Commun. 179 1
Google Scholar
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