Abstract
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.
Highlights
Metamaterials have been proposed for several innovative applications and have allowed, for example, the design of “perfect lenses” [1], and invisibility cloaks [2]
We assume that Rhodamine 800 (R800) dye molecules are dispersed into the dielectric core as in Fig. 1(b), and we use the same four level system as in the previous example
We focus on the frequency region 400-440 THz, and we consider concentrations relative to 5 mM and 10 mM of R800 dye molecules in the dielectric core, optically pumped at 680 nm with pumping rate Γpump = 6.5×109 s−1
Summary
Metamaterials have been proposed for several innovative applications and have allowed, for example, the design of “perfect lenses” [1], and invisibility cloaks [2]. At infrared, ultraviolet and optical frequencies, the use of plasmonics mixed with active photonic materials has been found to be promising due to the fact that the gain experienced through the emission of a gain medium is capable of counteracting the high attenuation experienced by the electromagnetic wave due to the presence of the metal. This may lead to loss-mitigated metamaterials, enabling effective permeability or low permittivity parameters at optical frequencies. The core radius is r1, with permittivity ε1; the shell outer radius is r2, with permittivity ε2; a, b and c are the periodicities along x-, y- and zdirection, respectively. (a) The shell is made of silver. (b) The shell is made of gold
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