Gain-enhanced nanoplasmonic metamaterials: ultrafast sub-wavelength emitters

Abstract

Nanoplasmonics and optical metamaterials have in the last 10–15 years emerged as a new paradigm in condensed matter optics and nanoscience, offering a fresh perspective on the world of optics. They enable efficient coupling of electromagnetic fields to the nanoscale: the world of biological and nonbiological molecules.1 This tight localization of light to truly nanoscopic dimensions—well below the diffraction limit for visible light— enhances its interaction with matter, paving the way for a multitude of classical and quantum nano-optics applications. However, metal optics suffer from inherent dissipative losses, which have persistently hampered many of the envisaged uses. Advances in the theoretical understanding and experimental fabrication of gain-enhanced nanoplasmonic metamaterials now promise to overcome these hindrances, potentially leading to novel nanophotonic components and devices. Dissipative losses in nanoplasmonics arise from the interaction of incident photons with quasi-free conduction electrons in metals, and therefore constitute an inherent feature of the responses ofmetal-based nanodevices. For truly sub-wavelength plasmonic structures, these losses follow universal laws, i.e., they do not depend on a particular geometric configuration, but rather only on the type of (usually noble) metal used. Typical damping rates ( ) are of the order of 100ps 1, requiring gain coefficients =c 103–104s 1 to compensate for the losses. As an alternative strategy, optical metamaterials pave the way toward nanoscale control of light at the fabrication level. However, such control needs to be modulated dynamically, on-demand and in real time. Both of the abovementioned challenges can be met by metamaterials with gain incorporated directly into their fabric. Figure 1. Schematic of a gain-enhanced plasmonic nano-fishnet metamaterial together with example profiles of the inversion (lower left) and electric-field amplitude. hm, hc, and hd denote the height of the metal, cladding, and dielectric layers, respectively, ax and ay are the width of the rectangular holes in the x and y direction, and p is the periodicity of the material.