Enhancement of terahertz absorption spectrum based on the angle multiplexing of the dielectric metasurface
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摘要:
利用太赫兹波段独特的指纹谱可以实现有机大分子的快速检测识别，然而微量物质的太赫兹吸收谱测量仍非常有挑战性。本文针对微量有机物，提出了一种基于介质超表面角度复用的太赫兹吸收谱增强检测方案。其中超表面衬底和十字单元结构均为高阻硅，具有高
Q 谐振特性。不同太赫兹波入射角对应的超表面响应曲线上的谐振峰频率可覆盖0.50~0.57 THz。超表面上覆盖0.5~2.5 µm乳糖薄膜作为待测物时，各入射角度对应的谐振峰幅度随待测物的吸收谱大幅度改变，其包络线组成的吸收谱峰值比没有十字单元结构时最多增强可达82.59倍。仿真结果表明该介质超表面经过角度复用可在宽带范围内有效增强太赫兹吸收谱，经过优化设计可用于检测不同特征峰微量有机物质。Abstract:The rapid detection and identification of organic macromolecules can be realized by using the unique fringerprint spectrum of the terahertz band, but the measurement of terahertz absorption spectrum of trace analyte is still challenging. We proposed a detection scheme of enhancement of terahertz absorption spectrum for trace organic analyte based on angle multiplexing of the dielectric metasurface. The substrate and the cross-unit structure of metasurface are both high-resistance silicon which has high-
Q resonances. The resonance frequency of the metasurface under terahertz incident with different angles can cover 0.50−0.57 THz. When a lactose film with the thickness of 0.5−2.5 μm as analyte is placed on the metasurface, the amplitude of the resonance peak corresponding to each incident angle changes greatly with the absorption spectrum of the analyte. The enhanced absorption spectrum built by the resonance frequencies envelope is 82.59 times larger than that without the cross-unit structure. The simulation results show that the metasurface has great potential to enhance the terahertz absorption spectrum through angle multiplexing, and it can be used to detect trace organic substances with different characteristic peaks after optimized design.-
Key words:
- terahertz /
- metasurface /
- absorption spectrum /
- angle multiplexing /
- enhancement
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图 1 基于介质超表面角度复用的太赫兹吸收谱增强检测原理示意图。（a）全硅介质超表面角度复用原理；（b）超表面的单元结构
Figure 1. Schematic diagram of enhanced detection of terahertz absorption spectrum based on dielectric metasurface angle multiplexing. (a) Angle multiplexing principle for all-silicon dielectric metasurface; (b) unit structure of the metasurface
图 2 超表面的反射曲线随（a）太赫兹波入射角α，（b）h，（c）w及（d）l的变化情况
Figure 2. The reflections of the metasurface with changing of (a) the incident angle, (b) h, (c) w and (d) l
图 3 超表面反射曲线的Q值随（a）太赫兹波入射角，（b）高度h，（c）宽度w
及（d）长度l的变化情况 Figure 3. Q values of the reflection curve of the metasurface varying with (a) the incident angle of the terahertz wave, (b) h, (c) w and (d) l
图 4 α-乳糖在0.45 THz~0.6 THz范围内的介电常数以及硅基底上涂布乳糖薄膜的响应曲线（0.50 THz~0.55 THz）。（a）介电常数；（b）反射率；（c）透射率；（d）吸收率
Figure 4. The dielectric constant of α-lactose at 0.45 THz~0.6 THz and the response curve of a film of lactose coated on a silicon (0.50 THz~0.55 THz). (a) dielectric constant; (b) reflectance; (c) transmittance; (d) absorptivity
图 5 基于角度复用介质超表面的乳糖太赫兹吸收谱增强。（a）涂敷乳糖薄膜的介质超表面单元结构；（b）超表面没有涂敷乳糖的反射率；（c）超表面没有涂敷乳糖时的透射率；（d）超表面涂敷2 μm乳糖的反射率；（e）超表面涂敷2 μm乳糖的透射率；（f）超表面涂敷2 μm乳糖的吸收率与无涂敷情况对比
Figure 5. Enhancement of the terahertz absorption spectrum of lactose on the dielectric metasurface based on angle multiplexing. (a) The metasurface unit structure of the medium coated with lactose film; (b) the reflectance of the metasurface without lactose coating; (c) the transmittance of the metasurface without lactose coating; (d) the reflection of metasurface coated with 2 μm lactose; (e) the transmittance of metasurface coated on the 2 μm lactosee; (f) absorption of metasurface with and without lactose coating
图 6 涂有乳糖薄膜介质超表面在角度复用时的电场分布。（a）α=25°（0.561 THz）；（b）α=35°（0.543 THz）；（c）α=45°（0.529 THz）；（d）α=55°（0.517 THz）
Figure 6. Electric field distributions of the dielectric metasurface coated with lactose film by multiplexing incident angle. (a) α=25° (0.561 THz); (b) α=35° (0.543 THz); (c) α=45° (0.529 THz); (d) α=55° (0.517 THz)
图 7 介质超表面涂敷不同厚度乳糖的增强吸收谱。（a）0.5 μm乳糖；（b）1.0 μm乳糖；（c）1.5 μm乳糖；（d）2.0 μm乳糖；（e）2.5 μm乳糖；（f）0.5~2.5 μm乳糖增强吸收谱（包络曲线）
Figure 7. Enhanced absorption spectra of dielectric metasurface coated with different thicknesses of lactose. (a) 0.5 μm lactose; (b) 1.0 μm lactose; (c) 1.5 μm lactose; (d) 2.0 μm lactose; (e) 2.5 μm lactose; (f) 0.5−2.5 μm lactose enhanced absorption spectra as envelope curves
表 1 本文结构与其它介质超表面或超光栅结构的吸收谱增强效果对比
Table 1. Comparison of absorption enhancement performances for the structure proposed in this paper and other metasufaces and metaragratings
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