We demonstrate the numerical and experimental realization of optimized optical traveling-wave antennas made of low-loss dielectric materials. These antennas exhibit highly directive radiation patterns and our studies reveal that this nature comes from two dominant guided TE modes excited in the waveguide-like director of the antenna, in addition to the leaky modes. The optimized antennas possess a broadband nature and have a nearunity radiation efficiency at an operational wavelength of 780 nm. Compared to the previously studied plasmonic antennas for photon emission, our all-dielectric approach demonstrates a new class of highly directional, low-loss, and broadband optical antennas.
We report on the fabrication and near field characterization of plasmonic slot waveguides in single- and poly crystalline gold films operating at telecommunication wavelengths. Moreover, we present freestanding photonic metasurfaces with a total thickness of only 40 nm prepared by focused ion beam milling of nanovoids in a carbon film followed by thermal evaporation of gold and plasma ashing of the carbon film.
Topological edge states draw their unique robustness against perturbations from a topological invariant of the bulk of the system. As long as the topological properties persist, the edge transport is not perturbed by static defects, which is referred to as the bulk-edge correspondence.
In our work we demonstrate that local periodic perturbations of the interface can destroy the topological protection even if the bulk of the system stays unperturbed. As model system we consider the Su-Schrieffer-Heeger (SSH) model realized in coupled plasmonic waveguide arrays with alternating short and long separations. Interfacing two SSH chains with different dimerizations we induce the topological edge mode. The temporal perturbations are realized by periodically bending the waveguide at the interface. The spatial evolution of surface plasmon polaritons (SPPs) in the array is monitored by real- and Fourier space leakage radiation microscopy. In Fourier space we observe that time-periodic perturbations of the interface create Floquet replicas of the topological edge mode. If the driving frequency is in the range for which the first Floquet replicas cross the static bands, the topological edge state couples to bulk states and the topological protection is destroyed resulting in delocalization of SPPs in real space. Otherwise the topological protection is conserved and SPPs stay localized at the interface. Our experimental findings are in full agreement with the theoretical analysis based on Floquet theory and illuminates the generalization of the bulk-edge correspondence for Floquet systems for the special case of a static bulk.
Previous experimental measurements and numerical simulations give evidence of strong electric and magnetic field interaction between split-ring resonators in dense arrays. One can expect that such interactions have an influence on the second harmonic generation. We apply the Discontinuous Galerkin Time Domain method and the hydrodynamic Maxwell-Vlasov model to simulate the linear and nonlinear optical response from SRR arrays. The simulations show that dense placement of the constituent building blocks appears not always optimal and collective effects can lead to a significant suppression of the near fields at the fundamental frequency and, consequently, to the decrease of the SHG intensity. We demonstrate also the great role of the symmetry degree of the array layout which results in the variation of the SHG efficiency in range of two orders of magnitude.
Transparent solids may absorb energy from a laser beam of sufficient high intensity. Several models are under
consideration to describe the evolution of the free-electron density. Some of these models keep track of the energy
distribution of the electrons. In this work we compare different models and give rules to estimate which one
is applicable. We present the inclusion of a term in the multiple rate equation approach, recently introduced,
describing fast recombination processes to exciton states. Moreover, we present experimental results with temporally
asymmetric femtosecond laser pulses, impinging on a surface of fused silica. We found different thresholds for
surface material modification with respect to an asymetric pulse and its time reversed counterpart. This difference
is due to a different time-and-intensity dependence of the main ionization processes, which can be controlled with
help of femtosecond shaped laser pulses.
KEYWORDS: Magnetism, Split ring resonators, Geometrical optics, Near infrared, Light scattering, Chemical elements, Metamaterials, Finite element methods, Polarization, Gold
It seems to be feasible in the near future to exploit the properties of left-handed metamaterials in the telecom or even in the optical regime. Recently, split ring-resonators (SRR's) have been realized experimentally in the near infrared (NIR) and optical regime.1, 2 In this contribution we numerically investigate light propagation through an array of metallic SRR's in the NIR and optical regime and compare our results to experimental results. We find numerical solutions to the time-harmonic Maxwell's equations by using advanced finite-element-methods (FEM). The geometry of the problem is discretized with unstructured tetrahedral meshes. Higher order, vectorial elements (edge elements) are used as ansatz functions. Transparent boundary conditions (a modified PML method3) and periodic boundary conditions4 are implemented, which allow to treat light scattering problems off periodic structures.
This simulation tool enables us to obtain transmission and reflection spectra of plane waves which are incident onto the SRR array under arbitrary angles of incidence, with arbitrary polarization, and with arbitrary wavelength-dependencies of the permittivity tensor. We compare the computed spectra to experimental results and investigate resonances of the system.
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