Experimental Validation of Strong Directional Selectivity in Nonsymmetric Metallic Gratings with a Subwavelength Slit

Strong directional selectivity is theoretically predicted and experimentally validated at the microwave frequencies in the beaming regime for a single subwavelength slit in nonsymmetric metallic gratings with double-side corrugations. The operation regime can be realized at a fixed angle of incidence when the surface-plasmon assisted transmission is significant within a narrow range of observation angles, if illuminating one of the grating interfaces, and tends to vanish for all observation angles, if illuminating the opposite interface. The studied effect is connected with asymmetry (nonreciprocity) in the beaming that occurs if the surface plasmon properties are substantially different for the two interfaces being well isolated from each other

Unveiling Long-Lived Hot-Electron Dynamics via Hyperbolic Meta-antennas

publishedVersionPeer reviewe

Suppressing the spectral shift of a polarization-independent nanostructure with multiple resonances

Resonances are the cornerstone of photonic applications in many areas of physics and engineering. The spectral position of a photonic resonance is dominated by the structure design. Here, we devise a polarization-independent plasmonic structure comprising nanoantennas with two resonances on an epsilon-near-zero (ENZ) substrate in order to loosen this correlation to obtain less sensitivity to geometrical perturbations of the structure. Compared with the bare glass substrate, the designed plasmonic nanoantennas on an ENZ substrate exhibit a nearly three-fold reduction only in the resonance wavelength shift near the ENZ wavelength as a function of antenna length.publishedVersionPeer reviewe

Hot Electron Dynamics in Ultrafast Multilayer Epsilon-Near-Zero Metamaterial

Realizing remarkable tunability in optical properties without sacrificing speed is critical to obtain all optical ultrafast devices. In this work, we investigate the ultrafast temporal behavior of optically tunable epsilon-near-zero (ENZ) metamaterials, operating in the visible spectral range. To perform this the ultrafast dynamics of the hot electrons is acquired by femtosecond pump-probe spectroscopy and studied based on two-temperature model (2TM). We show that pumping with femtosecond pulses changes the effective permittivity of the metamaterial more than 400 %. This significant modulation is more pronounced in ENZ region and we confirm this by the 2TM. The realized ultrafast modulation in effective permittivity, along with the ultrashort relaxation time of 3.3 ps, opens a new avenue towards ultrafast photonic applications.Comment: 5 figure

Epsilon-near-zero nanoparticles

In this work, we propose epsilon-near-zero (ENZ) nanoparticles formed of metal and dielectric bilayers and employ the effective medium approach for multilayered nanospheres to study their optical response. We obtained a passive tunable ENZ region by varying the radii of the proposed bilayer nanospheres, ranging from visible to near-IR. In addition, we present the absorption and scattering cross-section of ENZ nanoparticles using an open-source, transfer-matrix-based software (STRATIFY). %, and a commercial FDTD software (LUMERICAL). The proposed ENZ nanoparticle is envisioned to be experimentally realized using chemical synthesis techniques

Experimental Verification of \u3cem\u3en\u3c/em\u3e = 0 Structures for Visible Light

We fabricate and characterize a metal-dielectric nanostructure with an effective refractive index n=0 in the visible spectral range. Light is excited in the material at deep subwavelength resolution by a 30-keV electron beam. From the measured spatially and angle-resolved emission patterns, a vanishing phase advance, corresponding to an effective ϵ=0 and n=0, is directly observed at the cutoff frequency. The wavelength at which this condition is observed can be tuned over the entire visible or near-infrared spectral range by varying the waveguide width. This n=0 plasmonic nanostructure may serve as a new building block in nanoscale optical integrated circuits and to control spontaneous emission as experimentally demonstrated by the strongly enhanced radiative optical density of states over the entire n=0 structure

Electrically Tunable Strongly Coupled Epsilon-Near-Zero and Plasmonic Hybrid Mode

Achieving active tunability of light and matter interaction is of great interest as it opens a new avenue for exploring various high-performance photonic devices. In this prospect, developing a novel way to achieve active tuning of a strongly coupled system is vital. Here, we demonstrated an active tuning of the coupling strength in a strongly coupled system comprised of a thin ITO film as epsilon-near-zero (ENZ) material and gold nanorods as plasmonic resonators. The incorporation of these two components exhibits strong coupling that manifests as spectral splitting in the transmission spectra in the near-infrared spectral range.acceptedVersionPeer reviewe

Ultrafast optical properties of stoichiometric and non-stoichiometric refractory metal nitrides TiNx, ZrNx, and HfNx

Refractory metal nitrides have recently gained attention in various fields of modern photonics due to their cheap and robust production technology, silicon-technology compatibility, high thermal and mechanical resistance, and competitive optical characteristics in comparison to typical plasmonic materials like gold and silver. In this work, we demonstrate that by varying the stoichiometry of sputtered nitride films, both static and ultrafast optical responses of refractory metal nitrides can efficiently be controlled. We further prove that the spectral changes in ultrafast transient response are directly related to the position of the epsilon-near-zero region. At the same time, the analysis of the temporal dynamics allows us to identify three time components - the "fast" femtosecond one, the "moderate" picosecond one, and the "slow" at the nanosecond time scale. We also find out that the non-stoichiometry does not significantly decrease the recovery time of the reflectance value. Our results show the strong electron-phonon coupling and reveal the importance of both the electron and lattice temperature-induced changes in the permittivity near the ENZ region and the thermal origin of the long tail in the transient optical response of refractory nitrides

Chiral metamaterials with negative refractive index based on four "U" split ring resonators

A uniaxial chiral metamaterial is constructed by double-layered four "U" split ring resonators mutually twisted by 90 degrees. It shows a giant optical activity and circular dichroism. The retrieval results reveal that a negative refractive index is realized for circularly polarized waves due to the large chirality. The experimental results are in good agreement with the numerical results.Comment: 4 pages, 4 figures, Published as cover on AP