One of the most important problems of metamaterials and metasurfaces research is the derivation and the analysis of the effective parameters. They allow to examine the structure without singling out each element and it is the significant advantage for practical use. Recently, it has been shown that in virtue of a subwavelength thickness metasurfaces can be described within an effective conductivity approach. Such an effective surface conductivity describes the properties of a metasurface in the far-field as well as in the near-field. We derive and analyze the effective surface conductivity of a plasmonic resonant anisotropic metasurface theoretically and numerically. With the help of obtained effective conductivity we study the near-field properties of this metasurface, in particular, the equal frequency contours of surface waves. We show the topological transition from elliptical to hyperbolic-like dispersion regime for the surface waves on a hyperbolic metasurface. Finally, we study the influence of spatial dispersion on the eigenmodes spectrum and analyze the hyperbolic regime of a metasurface with strong spatial dispersion.
KEYWORDS: Plasmonics, Near field optics, Near field scanning optical microscopy, Solar cells, Thin film solar cells, Silver, Metals, Electron beam lithography, Photovoltaics, Nanoantennas
Domino modes are highly-confined collectivemodes that were first predicted for a periodic arrangement of metallic
parallelepipeds in far-infrared region. The main feature of domino modes is the advantageous distribution of the
local electric field, which is concentrated between metallic elements (hot spots), while its penetration depth in
metal is much smaller than the skin-depth. Therefore, arrays of non-resonant plasmonic nanoantennas exhibiting
domino modes can be employed as broadband light trapping coatings for thin-film solar cells. However, until
now in the excitation of such modes was demonstrated only in numerical simulations. Here, we for the first
time demonstrate experimentally the excitation of optical domino modes in arrays of non-resonant plasmonic
nanoantennas. We characterize the nanoantenna arrays produced by means of electron beam lithography both
experimentally using an aperture-type near-field scanning optical microscope and numerically. The proof of
domino modes concept for plasmonic arrays of nanoantennas in the visible spectral region opens new pathways
for development of low-absorptive structures for effective focusing of light at the nanoscale.
We report on experimental and theoretical investigations of light diffraction from opal films of different thickness.
A special attention was paid to the transformation of diffraction patterns upon building up the opal structure from two-dimensional
(2D) film structure towards bulk three-dimensional (3D) structure. In our setup the diffraction patterns are
displayed on a narrow cylindrical screen with a specimen fixed in its center. The diffraction patterns have been studied
visually and recorded in different scattering geometries with the films illuminated with white unpolarized light. With
increasing number of layers, certain regions of 2D diffraction patterns fade out and finally form diffraction spots
characteristic for 3D diffraction. We also found that stacking faults in bulk opals lead to formation of a 2D-like
diffraction pattern, i.e. such structure demonstrate 3D to quasi-2D transition in optical properties.
We report on an analytical study of the photonic band structure of 2D and 3D multi-component photonic crystals. It is found that both types of crystal demonstrate a quasiperiodic resonant behavior of (hkl) photonic stop-bands as a function of the reciprocal lattice vector, providing a selective ON/OFF switching of nonresonant (hkl) stop-bands. Our predictions are compared with the results of conventional numerical studies using the photonic Korringa-Kohn-Rostocker method. Experimental transmission spectra of a-SiO2 synthetic opals show the OFF-switching of the {111} stop-bands at the filler permittivity of ~1.82, the {200} bands at ~1.63, the {220} bands at ~1.93, and the {311} bands at ~1.75. The (222) photonic stop-band, which is due to the second order diffraction from the (111) planes, cannot be switched OFF in a wide range of filler permittivity values, thus indicating a resonant behavior. The experimental data demonstrate an excellent agreement with the theoretical predictions.
We suggest a new approach to the study of photonic crystals, based on direct visualisation of the photonic bandgap structure from Bragg diffraction patterns. Using high quality synthetic opals as photonic crystals, we have demonstrated how the Bragg diffraction of light can provide observation and analysis of the photonic band gap structure. We observed directly and photographed Bragg diffraction patterns as symmetrical sets of color spots on a screen, which appeared, displaced and disappeared, as the crystal was rotated relative to the incident laser beam. The diffraction patterns were observed under laser illumination with different wavelengths. The analysis of the experimental data can provide the number and orientation of the crystallographic planes responsible for the Bragg diffraction, as well as information about disorder in opal structure.
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