Department of Physics and Astronomy, Western Washington University, Bellingham, Washington, United States of America.
Department of Chemistry, Western Washington University, Bellingham, Washington, United States of America.
PLoS One. 2022 Oct 26;17(10):e0276522. doi: 10.1371/journal.pone.0276522. eCollection 2022.
A surface plasmon polariton (SPP) is an excitation resulting from the coupling of light to a surface charge oscillation at a metal-dielectric interface. The excitation and detection of SPPs is foundational to the operating mechanism of a number of important technologies, most of which require SPP excitation via direct reflectance, commonly achieved via Attenuated Total Reflection (ATR) using the Kretschmann configuration. As a result, the accessible modes are fundamentally high-loss "leaky modes," presenting a critical performance barrier. Recently, our group provided the first demonstration of "forbidden," or guided-wave plasmon polariton modes (GW-PPMs), collective modes of a MIM structure with oscillatory electric field amplitude in the central insulator layer with up to an order of magnitude larger propagation lengths than those of traditional SPPs. However, in that work, GW-PPMs were accessed by indirect reflectance using Otto configuration ATR, making them of limited applied relevance. In this paper, we demonstrate a technique for direct reflectance excitation and detection of GW-PPMs. Specifically, we replace the air gap used in traditional Otto ATR with a low refractive index polymer coupling layer, mirroring a technique previously demonstrated to access Long-Range Surface Plasmon Polariton modes. We fit experimental ATR data using a robust theoretical model to confirm the character of the modes, as well as to explore the potential of this approach to enable advantageous propagation lengths. The ability to excite GW-PPMs using a device configuration that does not require an air gap could potentially enable transformative performance enhancements in a number of critical technologies.
表面等离激元（SPP）是一种光与金属-电介质界面上的表面电荷振荡耦合产生的激发。SPP 的激发和检测是许多重要技术的工作机制基础，其中大多数技术需要通过衰减全反射（ATR）利用 Kretschmann 配置直接反射来实现 SPP 激发。因此，可获得的模式本质上是高损耗的“泄漏模式”，这构成了一个关键的性能障碍。最近，我们小组首次展示了“禁戒”或导波等离激元模式（GW-PPM），这是一种具有在中央绝缘层中振荡电场幅度的 MIM 结构的集体模式，其传播长度比传统 SPP 大一个数量级。然而，在这项工作中，GW-PPM 是通过奥托配置 ATR 的间接反射来获得的，这使得它们的应用相关性有限。在本文中，我们展示了一种用于直接反射激发和检测 GW-PPM 的技术。具体来说，我们用低折射率聚合物耦合层取代了传统奥托 ATR 中的气隙，这模仿了一种先前演示过的技术，用于获得长程表面等离激元模式。我们使用稳健的理论模型拟合实验 ATR 数据，以确认模式的特征，并探索这种方法在实现有利传播长度方面的潜力。使用不需要气隙的器件配置来激发 GW-PPM 的能力，有可能在许多关键技术中实现变革性的性能提升。
