The concept of an ultra-thin metasurface made of single layer of only-dielectric disks for successful phase control over a full range is demonstrated. Conduction loss is avoided compared to its plasmonic counterpart. The interaction of the Mie resonances of the first two modes of the dielectric particles, magnetic and electric dipoles, is tailored by the dimensions of the disks, providing required phase shift for the transmitted beam from 0° to 360°, together with high transmission efficiency. The successful performance of a beam-tilting array and a large-scale lens functioning at 195 THz demonstrates the ability of the dielectric metasurface that is thin and has also high efficiency of more than 80%. Such configurations can serve as outstanding alternatives for plasmonic metasurfaces especially that it can be a scalable design.

Green sulfur bacteria are an iconic example of nature’s adaptation: thriving in environments of extremely low photon density, the bacterium ranks itself among the most efficient natural light-harvesting organisms. The photosynthetic antenna complex of this bacterium is a self-assembled nanostructure, ≈60 × 150 nm, made of bacteriochlorophyll molecules. We study the system from a computational nanoscience perspective by using electrodynamic modeling with the goal of understanding its role as a nanoantenna. Three different nanostructures, built from two molecular packing moieties, are considered: a structure built of concentric cylinders of aggregated bacteriochlorophyll d monomers, a single cylinder of bacteriochlorophyll c monomers, and a model for the entire chlorosome. The theoretical model captures both coherent and incoherent components of exciton transfer. The model is employed to extract optical spectra, concentration and depolarization of electromagnetic fields within the chlorosome, and fluxes of energy transfer for the structures. The second model nanostructure shows the largest field enhancement. Further, field enhancement is found to be more sensitive to dynamic noise rather than structural disorder. Field depolarization, however, is similar for all structures. This indicates that the directionality of transfer is robust to structural variations, while on the other hand, the intensity of transfer can be tuned by structural variations.

Fast and efficient calculations of optical responses using electromagnetic models require computational acceleration and compression techniques. A hierarchical matrix approach is adopted for this purpose. In order to model large-scale molecular structures these methods should be applied over wide frequency spectra. Here we introduce a novel parametric hierarchical matrix method that allows one for a rapid construction of a wideband system representation and enables an efficient wideband solution. We apply the developed method to the modeling of the optical response of bacteriochorophyll tubular aggregates as found in green photosynthetic bacteria. We show that the parametric method can provide one with the frequency and time-domain solutions for structures of the size of 100, 000 molecules, which is comparable to the size of the whole antenna complex in a bacterium. The absorption spectrum is calculated and the significance of electrodynamic retardation effects for relatively large structures, i.e. with respect to the wavelength of light, is briefly studied. PACS numbers: INTRODUCTIONThe prediction of optical properties is one of the main challenges for the theoretical characterization of molecular aggregates [1][2][3][4]. The complication originates in the disorder and structural variations that span over a broad length scale and include fluctuations of monomer transition frequencies, domain formation and variations in the aggregate shape on the submicron scale [5][6][7]. The periodic lattice approximation is hardly applicable in this case and one may need to model the complete structure. Quantum mechanical methods, for example, open quantum system approaches [8] or quantum mechanics/molecular mechanics methods [9], that became popular recently, can characterize aggregate-light interaction in great details. However, the application of these methods to large systems is constrained by the exponential complexity growth with respect to the number of monomers composing the structure.Aggregates of pigments molecules and fluorescent dyes possess distinct optical properties such as strong absorbance and fluorescence, coherent interaction with photons, and also fast and long-range diffusion of the absorbed energy among the molecules composing the aggregate [1]. There are a number of examples of molecular aggregates. For instance, light-absorbing complexes in plants and photosynthetic bacteria contain aggregates of pigment molecules, chlorophylls and bacteriochlorophylls respectively [2]. Those structures, constructed by nature, collect and process solar energy with high efficiency. Molecular aggregates can also be grown using self-assembly methods in different shapes including pseudo one-dimensional chains [5] two-dimensional films [6] and nanoscale tubes [7,10]. Molecular aggregates can be combined with other photonic structures such as optical cavities [3] or plasmonic nanoparticles [4]. Thus, the interest to molecular aggregates as possible lightprocessing elements grows continuously.In this context, the classical el...

A hybrid surface integral equation solver based on the hierarchical matrix, the integral equation fast Fourier transform method and the equivalent surface method is developed for simulation of (pseudo-) periodic optical metamaterial problems. The solver is typically suitable for problems with (1) large periodic supercell or aperiodic cell arrays, (2) dominance of near field interactions, (3) presence of deep subwavelength features and (4) high geometry surface to volume ratio. An integral equation accelerator is introduced which uses a four to six level block Toeplitz matrix structure which naturally maps to the pseudo-periodic structure of metamaterial array problems, eliminates the need for the correction process encountered in fast Fourier transform-based methods and leads to substantial recycling of near field matrices. Novel metamaterial designs such as a supercell metamaterials, an aperiodic metasurfaces an a surface Luneburg lens are presented and solved, verifying the efficiency and accuracy of the presented model.