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Fourier-plane investigation of plasmonic bound states in the continuum and molecular emission coupling
Nanophotonics ( IF 7.5 ) Pub Date : 2020-09-02 , DOI: 10.1515/nanoph-2020-0343
In Cheol Seo 1 , Seongheon Kim 1 , Byung Hoon Woo 1 , Il-Sug Chung 2 , Young Chul Jun 1
Affiliation  

Abstract Bound states in the continuum (BICs) or trapped modes can provide an important new avenue for strong light confinement via destructive interference. Dielectric photonic structures have been extensively studied for optical BICs. However, BICs in plasmonic nanostructures have not been explored much yet. Herein, we present a thorough experimental study of plasmonic BICs via Fourier-plane spectroscopy and imaging. Optical mode dispersion in a metal grating covered by a dielectric layer is directly measured in an angle-resolved white light reflection spectrum. Two dielectric layer thicknesses are considered. Both plasmonic and photonics modes are supported in the visible range using a thicker dielectric film; hence, either hybrid or purely plasmonic BICs can be formed. With a thinner dielectric layer, only plasmonic modes are strongly excited and purely plasmonic BICs appear. Our measurements exhibit all features expected for BICs, including a substantial increase in the Q factor. We also demonstrate that the BIC position can be switched from one optical mode branch to the other by tuning a metal grating parameter. Moreover, by mixing luminescent dyes in a dielectric layer, light emission coupling into BICs is investigated. We find that the photoluminescence peak disappears at the BIC condition, which is attributed to the trapping of molecular emission at plasmonic BICs. Therefore, both white light reflection and dye emission measurements in the Fourier plane clearly indicate the formation of trapped modes in plasmonic nanostructures. Our observation implies that plasmonic BICs can enable a highly effective light trapping device despite the simple structure of the device geometry. Plasmonic supercavity design based on the BIC concept may provide many interesting future opportunities for nanolasers, optical sensing, and nonlinear enhancement.

中文翻译:

连续介质和分子发射耦合中等离子体束缚态的傅里叶平面研究

摘要 连续谱中的束缚态 (BIC) 或俘获模式可以通过相消干涉为强光限制提供重要的新途径。介电光子结构已被广泛研究用于光学 BIC。然而,等离子体纳米结构中的 BIC 还没有得到太多探索。在此,我们通过傅里叶平面光谱和成像对等离子体 BIC 进行了彻底的实验研究。由介电层覆盖的金属光栅中的光学模式色散直接在角分辨白光反射光谱中测量。考虑了两种介电层厚度。使用较厚的介电膜在可见光范围内支持等离子体和光子模式;因此,可以形成混合或纯等离子体 BIC。具有较薄的介电层,只有等离子体模式被强烈激发并且出现纯等离子体 BIC。我们的测量显示了 BIC 预期的所有特征,包括 Q 因子的大幅增加。我们还证明了 BIC 位置可以通过调整金属光栅参数从一个光模分支切换到另一个。此外,通过在介电层中混合发光染料,研究了光发射耦合到 BIC。我们发现光致发光峰在 BIC 条件下消失,这归因于分子发射在等离子体 BIC 处的捕获。因此,傅立叶平面中的白光反射和染料发射测量清楚地表明等离子体纳米结构中捕获模式的形成。我们的观察表明,尽管器件几何结构简单,但等离子体 BIC 可以实现高效的光捕获器件。基于 BIC 概念的等离子体超腔设计可能为纳米激光器、光学传感和非线性增强提供许多有趣的未来机会。
更新日期:2020-09-02
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