Title Complex modes and near-zero permittivity in 3 D arrays of plasmonic nanoshells : loss compensation using gain (original) (raw)
Related papers
Optical Materials Express, 2011
We report on the possibility of adopting active gain materials (specifically, made of fluorescent dyes) to mitigate the losses in a 3D periodic array of dielectric-core metallic-shell nanospheres. We find the modes with complex wavenumber in the structure, and describe the composite material in terms of homogenized effective permittivity, comparing results from modal analysis and Maxwell Garnett theory. We then design two metamaterials in which the epsilon-near-zero frequency region overlaps with the emission band of the adopted gain media, and we show that metamaterials with effective parameters with low losses are feasible, thanks to the gain materials. Even though fluorescent dyes embedded in the nanoshells' dielectric cores are employed in this study, the formulation provided is general, and could account for the usage of other active materials, such as semiconductors and quantum dots.
Photonic and Phononic Properties of Engineered Nanostructures II, 2012
Composite materials based on plasmonic nanoparticles allow building metamaterials with very large effective permittivity (positive or negative) or ε-near-zero; moreover, if clustered or combined with other nanoparticles, it is possible to generate also effective magnetic permeability (positive or negative), and an ad-hoc design would result in the generation of double negative materials, and therefore backward wave propagation. However, losses are usually significant and affect the metamaterial performance. In this work, we report on the possibility of adopting fluorescent dye molecules or quantum dots, optically pumped, embedded into the dielectric cores of the employed nanoshell particles, and provide loss-compensation in ordered 3D periodic arrays at optical frequencies. Each spherical nanoshell is modeled as an electric dipole. We consider nanoparticles with gold and silver shells. We then find the modes with complex wavenumber in the metamaterial, and describe the composite material in terms of homogenized effective material parameters (refractive index and permittivity). Furthermore, in case of loss-compensation, we compare the results obtained from modal analysis with the ones computed by using two different homogenization methods: (i) Maxwell Garnett homogenization theory and (ii) Nicholson-Ross-Weir retrieval method. We show the design of two εnear-zero metamaterials with low losses by simulating gain material made of dyes or quantum dots with realistic parameters. A brief discussion about the employment of the two kinds of active gain materials adopted here is given in the end.
Complex modes and effective refractive index in 3D periodic arrays of plasmonic nanospheres
Optics Express, 2011
We characterize the modes with complex wavenumber for both longitudinal and transverse polarization states (with respect to the mode traveling direction) in three dimensional (3D) periodic arrays of plasmonic nanospheres, including metal losses. The Ewald representation of the required dyadic periodic Green's function to represent the field in 3D periodic arrays is derived from the scalar case, which can be analytically continued into the complex wavenumber space. We observe the presence of one longitudinal mode and two transverse modes, one forward and one backward. Despite the presence of two modes for transverse polarization, we notice that the forward one is "dominant" (i.e., it contributes most to the field in the array). Therefore, in case of transverse polarization, we describe the composite material in terms of a homogenized effective refractive index, comparing results from (i) modal analysis, (ii) Maxwell Garnett theory, (iii) Nicolson-Ross-Weir retrieval method from scattering parameters for finite thickness structures (considering different thicknesses, showing consistency of results), and (iv) the fitting of the fields obtained through HFSS simulations. The agreement among the different methods justifies the performed homogenization procedure in case of transverse polarization.
Gain induced optical transparency in metamaterials
Applied Physics Letters, 2011
We demonstrate that fluorophores coupled to plasmonic nanoparticles promote resonant excitation energy transfer processes leading to low-loss building block metamaterials. Experimental observations of Rayleigh scattering enhancement, accompanied by an increase in transmission as function of the gain, clearly reveal optical loss compensation effects. Fluorescence quenching is also observed in gain assisted nanoparticles owing to the increase in nonradiative decay rate triggered by plasmonic resonances. The gain induced transparency at optical frequencies is an unambiguous consequence of loss reduction in metamaterial subunits, representing a promising step to enable a wide range of electromagnetic properties of optical metamaterials.
New Journal of Physics, 2012
We investigate enhanced harmonic generation processes in gainassisted, near-zero permittivity metamaterials composed of spherical plasmonic nanoshells. We report the presence of narrow-band features in transmission, reflection and absorption induced by the presence of an active material inside the core of the nanoshells. The damping-compensation mechanism used to achieve the near-zero effective permittivity condition also induces a significant increase in field localization and strength and, consequently, enhancement of linear absorption. When only metal nonlinearities are considered, second-and third-harmonic generation efficiencies obtained by probing the structure in the vicinity of the near-zero permittivity condition approach values as high as 10 −7 for irradiance value as low as 10 MW cm −2 . These results clearly demonstrate that a relatively straightforward path now exists for the development of exotic and extreme nonlinear optical phenomena in the kW cm −2 range. 4 These authors contributed equally to this work.
Characterization of the optical modes in 3D-periodic arrays of metallic nanospheres
2011 XXXth URSI General Assembly and Scientific Symposium, 2011
Complex optical modes in 3D-periodic arrays of metallic nanospheres are analyzed at optical frequencies for both longitudinal and transversal (with respect to the mode traveling direction) polarization states. Each nanosphere of the array is modeled to act as a single dipole by using the single dipole approximation approach, and the metal permittivity is described by the Drude model. Complex mode dispersion diagrams, the figure of merit and effective refractive index versus frequency are shown and compared with those obtained with Maxwell Garnett homogenization theory. Comparison with effective permittivity retrieved by scattering parameters of finite-thickness structures will be shown during the presentation.
2011
Optical losses in meta-structures based on metal subunits represents a central topic towards the fabrication of metamaterials in the visible range, since most of the extra-ordinary electromagnetic properties expected in these structured systems are shadowed by unavoidable absorptive effects. In this paper we report experimental studies aimed to demonstrate effective chemical and physical approaches to mitigate the radiation damping effect by means of ”gain assisted” and ”gain functionalized” coreshell metal nanospheres selected as metamaterial building blocks. A multiscale strategy has been utilized to compare these two systems, showing that in both cases partial loss compensation can be obtained.
Gain and plasmon dynamics in loss-compensated negative-index metamaterials
Photonic metamaterials allow for a range of exciting applications unattainable with ordinary dielectrics. However, the metallic nature of their meta-atoms may result in increased optical losses. Gain-enhanced metamaterials are a potential solution to this problem, but the conception of realistic, three-dimensional designs is a challenging task. Starting from fundamental electrodynamic and quantummechanical equations we establish and deploy a rigorous theoretical model for the spatial and temporal interaction of lightwaves with free and bound electrons inside and around metallic (nano-) structures and gain media. The derived numerical framework allows us to self-consistently study the dynamics and impact of the coherent plasmon-gain interaction, nonlinear saturation, field enhancement, radiative damping and spatial dispersion. Using numerical pump-probe experiments on a double-fishnet metamaterial structure with dye molecule inclusions we investigate the build-up of the inversion profile and the formation of the plasmonic modes in the low-Q cavity. We find that full loss compensation occurs in a regime where the real part of the effective refractive index of the metamaterial becomes more negative compared to the passive case. Our results provide a deep insight into how internal processes affect the over-all optical properties of active photonic metamaterials fostering new approaches to the design of practical loss-compensated plasmonic nanostructures.
Loss and gain in metamaterials
Journal of the Optical Society of America B, 2010
A double-periodic array of pairs of parallel gold nanorods is shown to have a negative refractive index in the optical range. Such behavior results from the plasmon resonance in the pairs of nanorods for both the electric and the magnetic components of light. The refractive index is retrieved from direct phase and amplitude measurements for transmission and reflection, which are all in excellent agreement with simulations. Both experiments and simulations demonstrate that a negative refractive index nЈ Ϸ −0.3 is achieved at the optical communication wavelength of 1.5 m using the array of nanorods. The retrieved refractive index critically depends on the phase of the transmitted wave, which emphasizes the importance of phase measurements in finding nЈ.
Gain-assisted plasmonic metamaterials: mimicking nature to go across scales
Rendiconti Lincei, 2015
Nature as a source of inspiration for designing and fabricating nanostructured materials with unconventional properties is an unparalleled driving force of this work leading to low-loss metamaterials. Here, we report about a multipronged approach to create optical metamaterials based on plasmonic nanostructures, hierarchical organization and interplay between plasmon elements and excitonic molecules. This work is focused on strategies and approaches to produce gain to metamaterials across scales with the aim of realizing low-loss optical materials and unlocking their unconvetional electromagnetic properties. Finally, we describe how a biomimetic approach based on gain-functionalized bionanoparticle can be harnessed for diagnostics and theranostics.