Resonant metasurfaces at oblique incidence: interplay of order and disorder.

Understanding the impact of order and disorder is of fundamental importance to perceive and to appreciate the functionality of modern photonic metasurfaces. Metasurfaces with disordered and amorphous inner arrangements promise to mitigate problems that arise for their counterparts with strictly periodic lattices of elementary unit cells such as, e.g., spatial dispersion, and allows the use of fabrication techniques that are suitable for large scale and cheap fabrication of metasurfaces. In this study, we analytically, numerically and experimentally investigate metasurfaces with different lattice arrangements and uncover the influence of lattice disorder on their electromagnetic properties. The considered metasurfaces are composed of metal-dielectric-metal elements that sustain both electric and magnetic resonances. Emphasis is placed on understanding the effect of the transition of the lattice symmetry from a periodic to an amorphous state and on studying oblique illumination. For this scenario, we develop a powerful analytical model that yields, for the first time, an adequate description of the scattering properties of amorphous metasurfaces, paving the way for their integration into future applications.

Huge local field enhancement in perfect plasmonic absorbers.

In this work we theoretically reveal the huge local field enhancement in a so-called perfect plasmonic absorber. We study the power absorption of light in a planar grid modelled as an effective sheet with zero optical thickness. The key prerequisite of the total absorption is the simultaneous presence of both resonant electric and magnetic modes in the structure. We show that the needed level of the magnetic mode is achievable using the effect of substrate-induced bianisotropy. On the microscopic level this bianisotropy is a factor which results in the huge local field enhancement at the same wavelength where the maximal absorption holds.

Additional effective medium parameters for composite materials (excess surface currents).

Modified boundary conditions for composite material are suggested. The modified RT-retrieval procedure yields bulk values of effective impedance and refractive index, which are independent of system size and boundary realization, whereas the conductivities of the excess surface currents depend on the property of the interface. Simultaneous treatment of all the possible realizations of the system removes the dependence. The accuracy of the latter procedure is the same as the usage of static effective parameters, namely k(eff)d.

Resonator mode in chains of silver spheres and its possible application.

A transversal mode with zero group velocity and nonzero phase velocity that can exist in chains of silver nanospheres in the optical frequency range is theoretically studied. It is shown that the external source radiating a narrow-band nonmonochromatic signal can excite in the chain a mixture of standing and slowly traveling waves. The standing-wave component (named the resonator mode) is strongly dominating. The physical reason for such a regime is a sign-varying distribution of power flux over the cross section of the chain. A possible application of the resonator mode for evanescent-wave enhancement and for subwavelength imaging in the visible is discussed.

Role of wave interaction of wires and split-ring resonators for the losses in a left-handed composite.

In this work the analytical model explaining the main reason of transmission losses in the known two-phase lattice of Smith, Schultz, and Shelby representing a uniaxial variant of left-handed medium (LHM) at microwaves is presented. The role of electromagnetic interaction between split-ring resonators (SRRs) and straight wires leading to the dramatic increase of ohmic losses in SRRs within the band when the meta-material becomes a LHM is clarified. This paper explains why in this structure, rather high transmission losses are observed in the experimental data, whereas these losses in a separate lattice of SRRs and in a lattice of wires are negligible at these frequencies.

Low-frequency spatial dispersion in wire media.

This work is dedicated to the theoretical analysis of wire media, i.e., lattices of perfectly conducting wires consisting of two or three doubly periodic arrays of parallel wires which are orthogonal to one another. An analytical method based on the local field approach is used. The explicit dispersion equations are presented and studied. The possibility of introducing a dielectric permittivity is discussed. The theory is validated by comparison with the numerical data available in the literature.

Example of bianisotropic electromagnetic crystals: the spiral medium.

In this paper the electromagnetic properties of bianisotropic electromagnetic crystals are studied. The crystals are assumed to be rectangular lattices of perfectly conducting helicoidal spirals. The analytical theory of dispersion and plane-wave reflection refers to the case when the spiral step and the radius are small compared to the wavelengths in the host medium. The periods of the lattice can be arbitrary. Explicit closed-form expressions are derived for the effective material parameters of the medium in the low-frequency regime. The medium eigenmodes are elliptically polarized, and one of them propagates without interaction with the lattice. As to the other eigenmode, the lattice has strong spatial dispersion even at extremely low frequencies in the direction along the spiral axes. Numerical examples are given. An analogy between the spiral medium and the medium of loaded wires is indicated.

Two-dimensional electromagnetic crystals formed by reactively loaded wires.

Two-dimensional electromagnetic crystals formed by rectangular lattices of thin ideally conducting cylinders periodically loaded by bulk reactive impedances are considered. An analytical theory of dispersion and reflection from this medium is presented. The consideration is based on the local field approach. The transcendental dispersion equation is obtained in the closed form and solved numerically. Different types of the loads such as inductive, capacitive, serial, and parallel LC circuits are considered. Typical dispersion curves and reflection coefficients are calculated and analyzed.