基于二维介质超表面的太赫兹指纹吸收谱增强

Terahertz fingerprint spectral sensing based on two-dimensional dielectric metasurfaces

摘要:

太赫兹谱是一种有潜力的无标记工具，然而由于太赫兹波和微量样品之间相互作用非常微弱，需要采用额外电磁场局域结构来增强吸收指纹谱。为此本文提出一种二维介质超表面结构，将微量分析物旋涂到平坦背面，通过超表面激发的倏逝波有效提升待测物附近的局域电磁场，并利用角度复用实现宽带太赫兹吸收谱增强。当太赫兹波以不同角度入射超表面结构时，激发的一系列导模共振峰频率可覆盖0.49THz~0.57THz。选择0.2 μm的α-乳糖薄膜作为待测微量分析物时，结构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该结构增强了180倍。该结构制作简单，样品制备方便，增强倍数高，为微量分析物的太赫兹指纹检测提供了一种新方法。

Abstract:

Teraherz(THz) spectroscopy provides a very promising label-free tool. However, the interaction between the terahertz wave and the trace analyte is very weak, and an additional structure for electromagnetic field localization is required to enhance the absorption fingerprint spectrum. In this paper, a two-dimensional metasurface structure is proposed, in which a trace analyte film is applied to the flatten surface, where the evanescent wave can effectively boost the local field around the analyte and enhance broadband terahertz absorption spectrum. When terahertz waves are incident on the metasurface structure at different angles, a series of wave-guide mode resonances can be excited, and the peak frequencies of the metasurface absorption resonance can cover 0.49THz ~ 0.57THz. When the 0.2 μm α-lactose film is selected as the trace analyte, the amplitude of the resonance peaks of the structure are changed according to the absorption spectrum of the analyte. The peaks envelop forming the enhanced absorption is 180-fold stronger than the film adsorption without the structure. This structure has the characteristics of simple fabrication, convenient sample preparation and high enhancement factor, which provides a new method for the terahertz fingerprinting detection of trace analytes.