Department of Photonics Engineering, Technical University of Denmark, DK-2800 Kgs. Lyngby, Denmark.
Opt Lett. 2012 Jul 1;37(13):2538-40. doi: 10.1364/OL.37.002538.
Giant field enhancement and field singularities are a natural consequence of the commonly employed local-response framework. We show that a more general nonlocal treatment of the plasmonic response leads to new and possibly fundamental limitations on field enhancement with important consequences for our understanding of surface-enhanced Raman spectroscopy (SERS). The intrinsic length scale of the electron gas serves to smear out assumed field singularities, leaving the SERS enhancement factor finite, even for geometries with infinitely sharp features. For silver nanogroove structures, mimicked by periodic arrays of half-cylinders (up to 120 nm in radius), we find no enhancement factors exceeding 10 orders of magnitude (10(10)).
巨场增强和场奇点是常用局部响应框架的自然结果。我们表明，对等离子体响应进行更一般的非局部处理会对场增强产生新的、可能的根本性限制，这对我们理解表面增强拉曼光谱（SERS）有重要意义。电子气的固有长度尺度有助于消除假设的场奇点，使 SERS 增强因子有限，即使对于具有无限尖锐特征的几何形状也是如此。对于银纳米槽结构，通过周期性排列的半圆柱（半径可达 120nm）进行模拟，我们发现增强因子不超过 10 个数量级（10(10)）。
