太赫兹波段金属线栅的紫外光控特性研究
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摘要
基于氧化铟纳米薄膜及金属线栅的特性,利用紫外激光诱导以金属线栅为衬底的氧化铟纳米结构,研究其对于太赫兹偏振透射的调制特性。实验中在金属线栅上滴入溶于乙醇的氧化铟溶液,并使溶液恰好浸润在金属线栅缝隙中,同时将加热台的温度调至340℃,对金属线栅中的氧化铟进行热退火。结果表明,氧化铟-金属线栅线长方向与太赫兹电场偏振方向垂直时,在低强度紫外光的照射下,该样品对太赫兹的透射强度有较为明显的衰减,当紫外光功率密度为7 mW·cm~(-2)时,样品对太赫兹的调制深度可达71%;当氧化铟-金属线栅线长方向与太赫兹电场偏振方向平行时,紫外光激发下的样品对太赫兹的调制效果明显减弱,当紫外光功率密度为7 mW·cm~(-2)时,调制深度约为20%。氧化铟纳米薄膜中存在的氧空位,使该材料对紫外光具有特殊响应。在无紫外光照射下,样品环境中的氧气分子被吸附到氧化铟表面,由于化学反应生成O~(2-)离子态。当用光子能量大于氧化铟禁带宽度的紫外光激发样品时,在氧化铟表面激发出电子空穴对,空穴会被氧化铟表面的O~(2-)离子态和缺陷态束缚,从而释放电子到导带,增强了样品的电导率。在太赫兹波频段内,透过氧化铟样品的太赫兹强度与氧化铟电导率有很好的相关性。金属线栅利用金属表面可存在的自由电子的振荡,使电场方向与线栅方向平行的太赫兹偏振光激发电子沿线栅方向振荡,当电子与金属晶格中的原子碰撞时,此偏振光发生衰减并伴随辐射;而电场方向与线栅方向垂直的太赫兹偏振光,由于周期性结构的限制,无法激发自由电子振荡,主要表现出透射特性。结合氧化铟的表面缺陷特性,紫外光可实现作为氧化铟-金属线栅结构的光控偏振开关作用,氧化铟-金属线栅结构偏振器能很好地应用于太赫兹波频段的光控偏振调制。
In this paper, modulation characteristics of terahertz polarization transmission are studied based on the character of indium oxide nanofilm and metal wire-grid, using sample, indium oxide nanostructure with metal wire-grid as substrate, which is induced by ultraviolet laser. In the experiment, the indium oxide solution dissolved in ethanol is dripped onto the metal wire-grid, and the solution is just soaked in the gap of the metal wire-grid. At the same time, the temperature of the heating table is adjusted to 340 ℃ to thermal annealing on the indium oxide in the metal wire-grid. The results demonstrate that when the longitudinal direction of indium oxide-metal wire-grid is perpendicular to the polarization direction of terahertz electric field, the transmission intensity of the sample to terahertz is obviously attenuated induced by the low-intensity ultraviolet laser. When the UV power density is 7 mW·cm~(-2), the modulation depth of terahertz induced by sample with UV laser can reach 71%. When the longitudinal direction of indium oxide-metal wire grid is parallel to the polarization direction of terahertz electric field, the modulation effect of the sample excited by UV laser on terahertz is obviously weakened. When the UV power density is 7 mW·cm~(-2), the modulation depth of terahertz induced by sample with UV laser is about 20%. The presence of oxygen vacancies in indium oxide nanofilm makes the material particularly responsive to UV laser. With the absence of UV laser, oxygen molecules in the sample environment are adsorbed to the surface of indium oxide, and the O~(2-) ion state is generated due to chemical reaction. When the sample is excited by UV laser with photon energy higher than the width of indium oxide band gap, electron hole pairs are excited on the surface of indium oxide, and the holes are bound by the O~(2-) ion state and defect state on the surface of indium oxide, so as to release electrons into the conduction band and enhance the conductivity of the sample. Terahertz transmission intensity of indium oxide samples has a good correlation with the conductivity of indium oxide in the terahertz frequency range. Using existence of free electrons oscillating on the metal surface, metal wire-grid makes the electric field direction of terahertz polarized wave which parallel to the longitudinal direction of the metal wire-grid excite the electrons oscillation along the metal wire-grid direction. When electrons collide with atoms in a metal lattice, the polarized wave decay with radiating. However, the terahertz polarized wave whose electric field direction is perpendicular to the longitudinal direction of indium oxide-metal wire grid cannot stimulate free electron oscillation due to the limitation of the periodic structure, and it mainly shows transmission characteristics.In combination with the surface defect characteristics of indium oxide, UV laser can be used as an optically controlled polarization switch of indium oxide-metal wire grid structure, and indium oxide-metal wire-grid structure polarizer can be well applied to optically controlled polarization modulation interahertz frequency range.
In this paper, modulation characteristics of terahertz polarization transmission are studied based on the character of indium oxide nanofilm and metal wire-grid, using sample, indium oxide nanostructure with metal wire-grid as substrate, which is induced by ultraviolet laser. In the experiment, the indium oxide solution dissolved in ethanol is dripped onto the metal wire-grid, and the solution is just soaked in the gap of the metal wire-grid. At the same time, the temperature of the heating table is adjusted to 340 ℃ to thermal annealing on the indium oxide in the metal wire-grid. The results demonstrate that when the longitudinal direction of indium oxide-metal wire-grid is perpendicular to the polarization direction of terahertz electric field, the transmission intensity of the sample to terahertz is obviously attenuated induced by the low-intensity ultraviolet laser. When the UV power density is 7 mW·cm~(-2), the modulation depth of terahertz induced by sample with UV laser can reach 71%. When the longitudinal direction of indium oxide-metal wire grid is parallel to the polarization direction of terahertz electric field, the modulation effect of the sample excited by UV laser on terahertz is obviously weakened. When the UV power density is 7 mW·cm~(-2), the modulation depth of terahertz induced by sample with UV laser is about 20%. The presence of oxygen vacancies in indium oxide nanofilm makes the material particularly responsive to UV laser. With the absence of UV laser, oxygen molecules in the sample environment are adsorbed to the surface of indium oxide, and the O~(2-) ion state is generated due to chemical reaction. When the sample is excited by UV laser with photon energy higher than the width of indium oxide band gap, electron hole pairs are excited on the surface of indium oxide, and the holes are bound by the O~(2-) ion state and defect state on the surface of indium oxide, so as to release electrons into the conduction band and enhance the conductivity of the sample. Terahertz transmission intensity of indium oxide samples has a good correlation with the conductivity of indium oxide in the terahertz frequency range. Using existence of free electrons oscillating on the metal surface, metal wire-grid makes the electric field direction of terahertz polarized wave which parallel to the longitudinal direction of the metal wire-grid excite the electrons oscillation along the metal wire-grid direction. When electrons collide with atoms in a metal lattice, the polarized wave decay with radiating. However, the terahertz polarized wave whose electric field direction is perpendicular to the longitudinal direction of indium oxide-metal wire grid cannot stimulate free electron oscillation due to the limitation of the periodic structure, and it mainly shows transmission characteristics.In combination with the surface defect characteristics of indium oxide, UV laser can be used as an optically controlled polarization switch of indium oxide-metal wire grid structure, and indium oxide-metal wire-grid structure polarizer can be well applied to optically controlled polarization modulation interahertz frequency range.
引文
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[5] Alius H,Dodel G.Infrared Phys.,1991,32:1.
[6] Chen Sai,Fan Fei,Miao Yinping,et al.Nanoscale,2016,8(8):4713.
[7] Ly Nguyen Le,Nguyen Manh Thang,Le Minh Thuy,et al.Opt.Commun.,2017,383:244.
[8] Xing Yuanyuan,Zhang Xiaoyu,Zhang Qiang,et al.Opt.Commun.,2018,415:115.
[9] Ameneh Nejati,Ferdows B Zarrabi,Maryam Rahimi,et al.Optik,2015,126(19):2153.
[10] He Y N,Zhang B,Shen J L,et al.Opt.Commun.,2015,356:595.
[11] Zhang B,He T,Shen J,et al.Opt.Lett.,2014,39(21):6110.
[12] Zhang B,Lv L F,Shen J L,et al.Appl.Phys.Lett.,2015,107(9):093301.
[13] Lee Gyuseok,Maeng Inhee,Kang Chul,et al.Appl.Phys.Lett.,2018,112:111101.
[14] Chen H T,Padilla W J,Zide J M O,et al.Opt.Lett.,2007,32(12):1620.
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[20] Ji H,Zhang B,Shen J,et al.Opt.Express,2018,26:7204.
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