Nonlocal Optical Properties Research Articles

二维典型纳米结构的非局域化光学特性研究

Due to the existence of the quantum effect, the characteristics of nanostructure is difficult to explain entirely based on classical mechanics method. With the development of the FDTD method, its application in the field of optics is becoming increasingly widespread. In this paper, based on finite difference time domain (FDTD) method to study the nonlocal optical properties of two-dimensional structures was applied directly. The existence conditions of local and nonlocal optical characteristics under different nanometer radius, the impact of structural shapes with their extinction cross section properties were also obtained. The numerical results clearly show that with the decrease of the nanometer structure size and the shape of the structure, the non-locality becomes more pronounced. Our theory and results can provide a reference for the practical design of new nanoscale devices.

Nonlocal optical properties in AlGaAs/GaAs coupled quantum well nanostructures

Nonlocal intersubband optical absorption properties in AlGaAs/GaAs coupled quantum well (CQW) nanostructures are investigated for a p-polarized light in the case of taking spatial nonlocality of optical response into account. The numerical results show that the spatial nonlocality of optical response can lead optical spectrum lines to have a radiation shift due to the nonlocal effects, and the spatial nonlocality is associated closely with the coupling effects between the potential wells of the CQW system. The dependence of the radiation shift on structure parameters of the CQW is clarified. It is also demonstrated that the maximal radiation shift and the least optical absorbance can be obtained by optimizing structure parameters of the CQW. These results may be constructive in designing nanomaterials with various nonlocality and observing the spatial nonlocal effects in experiment.

Nonlocal optical properties in periodic lattice of graphene layers

Based on the effective medium model, nonlocal optical properties in periodic lattice of graphene layers with the period much less than the wavelength are investigated. Strong nonlocal effects are found in a broad frequency range for TM polarization, where the effective permittivity tensor exhibits the Lorentzian resonance. The resonance frequency varies with the wave vector and coincides well with the polaritonic mode. Nonlocal features are manifest on the emergence of additional wave and the occurrence of negative refraction. By examining the characters of the eigenmode, the nonlocal optical properties are attributed to the excitation of plasmons on the graphene surfaces.

Low-damping epsilon-near-zero slabs: Nonlinear and nonlocal optical properties

We investigate second harmonic generation, low-threshold multistability, all-optical switching, and inherently nonlocal effects due to the free-electron gas pressure in an epsilon-near-zero (ENZ) metamaterial slab made of cylindrical, plasmonic nanoshells illuminated by TM-polarized light. Damping compensation in the ENZ frequency region, achieved by using gain medium inside the shells' dielectric cores, enhances the nonlinear properties. Reflection is inhibited and the electric field component normal to the slab interface is enhanced near the effective pseudo-Brewster angle, where the effective \epsilon-near-zero condition triggers a non-resonant, impedance-matching phenomenon. We show that the slab displays a strong effective, spatial nonlocality associated with leaky modes that are mediated by the compensation of damping. The presence of these leaky modes then induces further spectral and angular conditions where the local fields are enhanced, thus opening new windows of opportunity for the enhancement of nonlinear optical processes.

Nonlocal optical properties in InGaN/GaN strained quantum wells with a strong built-in electric field

Based on the microscopic nonlocal optical response theory, the linear and nonlinear intersubband optical absorption properties in InyGa1−yN/GaN strained single quantum wells (SQWs) with a strong built-in electric field are investigated. The numerical results show that the optical absorption spectrum has an obvious blueshift originating from the nonlocal optical responses. The dependence of the blueshift on the SQW width and the mixing fraction y is clarified. In addition, the influence of the SQW structural parameters, the incident light intensity, and the incident angle on the optical absorption properties is demonstrated. These properties are desirable for controlling the nonlocal effect and optical absorption loss in optical device application.

Calculating nonlocal optical properties of structures with arbitrary shape

In a recent Letter [J. M. McMahon, S. K. Gray, and G. C. Schatz, Phys. Rev. Lett. 103, 097403 (2009)], we outlined a computational method to calculate the optical properties of structures with a spatially nonlocal dielectric function. In this paper, we detail the full method and verify it against analytical results for cylindrical nanowires. Then, as examples of our method, we calculate the optical properties of Au nanostructures in one, two, and three dimensions. We first calculate the transmission, reflection, and absorption spectra of thin films. Because of their simplicity, these systems demonstrate clearly the longitudinal (or volume) plasmons characteristic of nonlocal effects, which result in anomalous absorption and plasmon blueshifting. We then study the optical properties of spherical nanoparticles, which also exhibit such nonlocal effects. Finally, we compare the maximum and average electric field enhancements around nanowires of various shapes to local theory predictions. We demonstrate that when nonlocal effects are included, significant decreases in such properties can occur.

Metallic nanofilms optical response description based on self-consistent theory

In this paper an interaction of ultrathin (∼1 nm) metal film (called metal nanofilm) with external optical radiation theoretically considered. It's shown that metal nanofilms have a substantially nonlocal optical properties. A frequency, angular and polarization dependencies of optical response considered.

Small metal particles: Non-local optical properties and quantum-size effects

Abstract In this work we survey some recent results concerning non-local optical effects and particle-size dependence for the optical properties of individual metallic particles. We start by giving a historical overview and a conceptual discussion on the subject of small particles, underlining their potential applications. Simplified optical response functions for a metallic sphere are introduced and duly illustrated to bring out the physical content. Particular emphasis is given to optical absorption, resonance effects and far-infrared properties exhibited by simple and noble metal particles having less than 100 Å radii. A comparison between the traditional (Mie) approach and the proposed non-local scheme is made and it leads to an increased understanding of the various mechanisms a small particle exhibits when screening an external electromagnetic field.

Tensor-product structure of a new electromagnetic propagator for nonlocal surface optics of metals

With emphasis on the physical interpretation, the structure of a recently constructed electromagnetic propagator describing, within the framework of the semiclassical infinite-barrier model, the nonlocal optical properties of adjacent vacuum-metal half-spaces, is analyzed. The tensor-product structure of the rotational-free and divergence-free parts of the propagator is determined, and the direct, the indirect, and the self-field contributions are identified. On the basis of a plane-wave expansion, the physical role of the different propagator terms is studied. The contributions to the propagator from the collective polariton and plasmon excitations are separated from those stemming from the electron-hole pair excitations. Via a damped-wave picture of the propagator, contact with a new local propagator formalism of Sipe is established. The flexibility of the present formalism is demonstrated by investigating (i) the excitation of nonlocal surface waves by an oscillating dipole and (ii) the concept of surface-dressed dipole polarizability in the nonlocal regime.