Metamaterials for optical and THz ranges: design and characterization

The thesis is devoted to the field of metamaterials (MtMs) - effectively continuous artificial composites with advantageous electromagnetic properties not normally met in nature. The main goal of the work is the engineering of MtMs with new and extreme electromagnetic properties and their electromagnetic characterization.  The first part of the thesis is focused on the artificial magnetism and isotropic negative permittivity and permeability in the near-infrared and visible ranges. Several design solutions based on resonant complex-shaped inclusions are proposed and studied analytically and numerically. In the first design utilization of clusters of plasmonic dimers leads to the negative permeability in the near-infrared range. Next suggested MtM consisting of the clusters of plasmonic triangular nanoprisms possesses isotropic negative permeability on the boundary between the near-infrared and visible ranges. The third design based on core-shell metal-dielectric particles allows for the isotropic negative refractive index in the near-infrared range.  The second part of the thesis is devoted to the problem of characterization of planar and bulk MtMs. At first, the applicability of the so-called Holloway-Kuester method is studied for the planar arrays of complex inclusions. It is shown, that despite the fact that the approach initially was developed for the arrays of solid particles in the quasi-static approximation, it is also applicable for the arrays of rather optically substantial resonant clusters of plasmonic nanoparticles. Then, the method of homogenization of bulk MtMs is suggested, based on the account of electromagnetic interaction between crystal planes forming an orthorhombic lattice. The method reveals the electromagnetic properties not covered by the standard quasi-static homogenization procedures.  The last research problem studied in the thesis is the engineering of planar multifunctional MtMs for the THz range. The suggested MtM consists of resonant metal stripes put on both sides of an elastic polymer film and allows for the combination of polarization transformation properties with sensitivity to the applied strain. The design is studied theoretically, numerically, and experimentally. For the last purpose an original fabrication method is developed, allowing for the rather simple creation of optically large samples. The fabricated sample experimentally demonstrates a high sensitivity to stretching in the transmission coefficient for the co-polarized field

Enhanced Efficiency of Light-Trapping Nanoantenna Arrays for Thin Film Solar Cells

We suggest a novel concept of efficient light-trapping structures for thin-film solar cells based on arrays of planar nanoantennas operating far from plasmonic resonances. The operation principle of our structures relies on the excitation of chessboard-like collective modes of the nanoantenna arrays with the field localized between the neighboring metal elements. We demonstrated theoretically substantial enhancement of solar-cell short-circuit current by the designed light-trapping structure in the whole spectrum range of the solar-cell operation compared to conventional structures employing anti-reflecting coating. Our approach provides a general background for a design of different types of efficient broadband light-trapping structures for thin-film solar-cell technologically compatible with large-area thin-film fabrication techniques

Basics of averaging of the Maxwell equations for bulk materials

Volume or statistical averaging of the microscopic Maxwell equations (MEs), i.e. transition from microscopic MEs to their macroscopic counterparts, is one of the main steps in electrodynamics of materials. In spite of the fundamental importance of the averaging procedure, it is quite rarely properly discussed in university courses and respective books; up to now there is no established consensus about how the averaging procedure has to be performed. In this paper we show that there are some basic principles for the averaging procedure (irrespective to what type of material is studied) which have to be satisfied. Any homogenization model has to be consistent with the basic principles. In case of absence of this correlation of a particular model with the basic principles the model could not be accepted as a credible one. Another goal of this paper is to establish the averaging procedure for bulk MM, which is rather close to the case of compound materials but should include magnetic response of the inclusions and their clusters. In the vast majority of cases the consideration of bulk materials means that we consider propagation of an electromagnetic wave far from the interfaces, where the eigenwave in the medium has been already formed and stabilized. In other words, in this paper we consider the possible eigenmodes, which could exist in the equivalent homogenized media, and the necessary math apparatus for an adequate description of these waves. A discussion about boundary conditions and layered MM is a subject of separate publication and will be done elsewhere