Herein, we numerically investigate terahertz photoconductive antennas (PCAs) based on optimized plasmonic nanostructures and absorption enhancement in nanocylinders. Metallic nanostructures playing an important role in nanophotonic applications are a hot topic nowadays. Such applications are possible due to their capability to focus or intensify electromagnetic fields close to the metal by employing excitation approach of surface plasmon polaritons. Plasmonic behavior in the visible to near-infrared light spectrum is achievable due to the metallic nanostructures employment. Herein, we study the absorption enhancement of silver and transparent-conducting oxides (TCO) nanocylinders with different diameters by means of effective medium approximation. This study also reports on the stronger enhancement in the case of TCO nanocylinders. The results show that resonant absorption amplitude and wavelength are dramatically affected by the thickness of the nanostructure as well as by the distances between nanocylinders. The outputs reported here provide a fertile ground for precise control of the nanowire structures for sensing and other enhanced optical applications. Because of compact structure, simple fabrication and room temperature operation, PCAs provide THz wave generation and detection. Moreover, PCAs are widely used in time domain THz imaging and spectroscopy systems for generating pulsed THz radiation. It is worthwhile noting, that in case of TCO nanocylinders, absorption enhancement for NIR wavelengths, being relevant for present THz generation setup, reaches up to 5-fold leading to 25-fold increase in THz radiation.
Spoof plasmons are bound electromagnetic waves (EM) at frequencies outside the plasmonic range mimicking (“spoofing”) surface plasmons (SPs), which propagate on periodically corrugated metal surfaces. In recent years, electromagnetic waves propagating at an interface between a metal and dielectric have been of significant interest. Although most plasmonic research so far has focused on the near-infrared and optical ranges of the electromagnetic spectrum (where noble metals support highly confined surface waves), there exists an increasing interest in transferring SPs-based photonics to lower frequencies. However, in these spectral ranges, noble metals behave like perfect electric conductors, whose surface charges are able to screen any external EM excitation with extreme efficiency, preventing the formation of a tightly bound SP. It has been shown that the binding of EM fields to a metal surface can be increased by its corrugation. A surface of a metal perforated with a one-dimensional periodic array of rectangular grooves has already been considered. The question that remains open is the calculation of the effective permittivities for arbitrary grooves. The number of works describing the calculation of the effective dielectric constants for the grooved surfaces is limited. Here we have obtained an analytical dispersion relation of spoof plasmons on an arbitrary perforated surface of a real metal. We have derived analytical expressions for calculation of the permittivities of arbitrary grooves. Based on those results we have determined the minimum spot size for a triangular groove structure.
Optical waveguides have been a subject of an intensive theoretical research, resulting in applications in several fields, and stimulated research in integrated optics. Homogeneous dielectric waveguides and their properties are covered in detail in many articles and textbooks. However, in waveguides loaded with arbitrary inhomogeneous dielectrics, analytical solutions are possible only for a limited number of permittivity profiles in simple geometries. The analysis of longitudinally inhomogeneous waveguides has been already proposed, but the main drawback of this approach is that it requires cumbersome and time-consuming integration. We therefore suggest to take this a step further by applying our new original analytical approach that does not require integration. The aim of this work is to establish a different method that is generally applicable to any vectorial time-dependent, anisotropic, non-linear, inhomogeneous, dissipative and dispersive media to analyze the field distribution of inhomogeneous 1-D and 2-D waveguides with symmetric and asymmetric permittivity profiles. Our initial consideration of slab problems with arbitrary profiles by means of analytical method shows a great deal of potential for use in applications in fields such as physics, and engineering.