Fractals: optical susceptibility and giant raman scattering

A theory is developed which describes the optical properties of fractal clusters (i.e. of aggregates of non-trivial Hausdorff dimension consisting of interacting monomer particles). It is shown that with respect to these properties fractal clusters differ significantly from both gases and condensed media. The interaction between the monomers is assumed to be dipole-dipole. The theory is based on the self-consistent field equations; it takes into account the fluctuation nature of the fractal cluster (considerable probability for approach of monomers to each other despite an asymptotically zero integral density). An expression is obtained for the linear susceptibility. Combination of the monomers with the formation of a cluster entails the splitting, shift and broadening of the monomer spectra. These changes depend strongly on the fractal (Hausdorff) dimension of the cluster but do not depend on the number of monomers in it (for a cluster of non-trivial dimension). On the other hand, the monomers partially retain their individuality and the susceptibility — its quasi-resonance nature. Broadening, like the imaginary part of the susceptibility, does not depend on dissipation in an individual monomer. It is predicted that giant Raman scattering may occur at an impurity particle fixed near one of the cluster monomers when excitation takes place in the absorption band of the cluster. The enhancement factor for the scattering is also determined by the fractal dimension.     

Nature of the fluorescent states of quinoline analogs of styryl and distyrylanthracene

Study of the photophysical properties of quinoline analogs of 9-styryl and 9,10-distyrylanthracenes showed that, in contrast to the case of 9-[-(2-quinolyl)vinyl]anthracene, the intramolecular geometrical relaxation process plays a decisive role in the formation of the excited state of 9,10-di-[-(2-quinolyl)vinyl]-anthracene.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 824–829, June, 1987.     

FDTD modeling of realistic semicontinuous metal films

We have employed a parallelized 3D FDTD (finite-difference time-domain) solver to study the electromagnetic properties of random, semicontinuous, metal films. The structural features of the simulated geometries are exact copies of the fabricated films and are obtained from SEM images of the films themselves. The simulation results show good agreement with the experimentally observed far-field spectra, allowing us to also study the nonlinear moments of the optical responses for these realistic nanostructures.     

Enhancement of single‑photon emission from nitrogen‑vacancy centers with TiN/(Al,Sc)N hyperbolic metamaterial

The broadband enhancement of single‑photon emission from nitrogen‐vacancy centers in nanodiamonds coupled to a planar multilayer metamaterial with hyperbolic dispersion is studied experimentally. The metamaterial is fabricated as an epitaxial metal/dielectric superlattice consisting of CMOS‐compatible ceramics: titanium nitride (TiN) and aluminum scandium nitride (Al_xSc_1‐xN). It is demonstrated that employing the metamaterial results in significant enhancement of collected single‑photon emission and reduction of the excited‐state lifetime. Our results could have an impact on future CMOS‐compatible integrated quantum sources.

     

Random replicators with high-order interactions

We use tools of the equilibrium statistical mechanics of disordered systems to study analytically the statistical properties of an ecosystem composed of N species interacting via random mutual interactions, as well as via deterministic self-interactions of order p>/=2. We show that the main effect of increasing the order of the interactions among the species is to make the system less competitive, in the sense that the fraction of extinct species is greatly reduced. In addition, we find that for p>2 there is a threshold value which gives a lower bound to the concentration of the surviving species, preventing then the existence of rare species and, consequently, increasing the robustness of the ecosystem to external perturbations.     

The effect of gain and absorption on surface plasmons in metal nanoparticles

The compensation of loss in metal by gain in interfacing dielectric has been demonstrated in a mixture of aggregated silver nanoparticles and rhodamine 6G dye. An increase of the quality factor of surface plasmon (SP) resonance was evidenced by the sixfold enhancement of Rayleigh scattering. The compensation of plasmonic losses with gain enables a host of new applications for metallic nanostructures, including low- or no-loss negative-index metamaterials. We have also predicted and experimentally observed a suppression of SP resonance in metallic nanoparticles embedded in dielectric host with absorption. PACS 61.46.Df; 73.20.Mf; 78.67.Bf     

Effect of metallic and hyperbolic metamaterial surfaces on electric and magnetic dipole emission transitions

Spontaneous emission patterns of electric and magnetic dipoles on different metallic surfaces and a hyperbolic metamaterial (HMM) surface were simulated using the dyadic Green’s function technique. The theoretical approach was verified by experimental results obtained by measuring angular-dependent emission spectra of europium ions on top of different films. The results show the modified behavior of electric and magnetic dipoles on metallic and HMM surfaces. The results of numerical calculations agree well with experimental data.