Sub-Wavelength Focusing in Inhomogeneous Media with a Metasurface Near Field Plate.

Overcoming the diffraction limit, which enables focusing much less than the wavelength, requires tailoring the evanescent spectrum of an aperture's field distribution. We model and simulate a corrugated near field plate, which can generate a sub-wavelength focus in inhomogeneous background media. All reactive coupling, between the metasurface near field plate and the focusing domain and among the corrugations in the metasurface, is taken into consideration with the finite element method, which we solve in combination with a constraint to generate a desired focus.

Tunable Superconducting Cavity using Superconducting Quantum Interference Device Metamaterials.

Here we consider a tunable superconducting cavity that can be used either as a tunable coupler to a qubit inside the cavity or as a tunable low noise, low temperature, RF filter. Our design consists of an array of radio-frequency superconducting quantum interference devices (rf SQUIDs) inside a superconducting cavity. This forms a tunable metamaterial structure which couples to the cavity through its magnetic plasma frequency.

Permanently reconfigured metamaterials due to terahertz induced mass transfer of gold.

We present a new technique for permanent metamaterial reconfiguration via optically induced mass transfer of gold. This mass transfer, which can be explained by field-emission induced electromigration, causes a geometric change in the metamaterial sample. Since a metamaterial's electromagnetic response is dictated by its geometry, this structural change massively alters the metamaterial's behavior.

Nonlinear terahertz metamaterials via field-enhanced carrier dynamics in GaAs.

We demonstrate nonlinear metamaterial split ring resonators (SRRs) on GaAs at terahertz frequencies. For SRRs on doped GaAs films, incident terahertz radiation with peak fields of ~20-160 kV/cm drives intervalley scattering. This reduces the carrier mobility and enhances the SRR LC response due to a conductivity decrease in the doped thin film.

Terahertz-field-induced insulator-to-metal transition in vanadium dioxide metamaterial.

Electron-electron interactions can render an otherwise conducting material insulating, with the insulator-metal phase transition in correlated-electron materials being the canonical macroscopic manifestation of the competition between charge-carrier itinerancy and localization. The transition can arise from underlying microscopic interactions among the charge, lattice, orbital and spin degrees of freedom, the complexity of which leads to multiple phase-transition pathways. For example, in many transition metal oxides, the insulator-metal transition has been achieved with external stimuli, including temperature, light, electric field, mechanical strain or magnetic field.

THz near-field Faraday imaging in hybrid metamaterials.

We report on direct measurements of the magnetic near-field of metamaterial split ring resonators at terahertz frequencies using a magnetic field sensitive material. Specifically, planar split ring resonators are fabricated on a single magneto-optically active terbium gallium garnet crystal. Normally incident terahertz radiation couples to the resonator inducing a magnetic dipole oscillating perpendicular to the crystal surface.

Time-resolved imaging of near-fields in THz antennas and direct quantitative measurement of field enhancements.

We investigate the interaction between terahertz waves and resonant antennas with sub-cycle temporal and λ/100 spatial resolution. Depositing antennas on a LiNbO₃ waveguide enables non-invasive electro-optic imaging, quantitative field characterization, and direct measurement of field enhancement (up to 40-fold). The spectral response is determined over a bandwidth spanning from DC across multiple resonances, and distinct behavior is observed in the near- and far-field.

Flexible metamaterial absorbers for stealth applications at terahertz frequencies.

We have wrapped metallic cylinders with strongly absorbing metamaterials. These resonant structures, which are patterned on flexible substrates, smoothly coat the cylinder and give it an electromagnetic response designed to minimize its radar cross section. We compare the normal-incidence, small-beam reflection coefficient with the measurement of the far-field bistatic radar cross section of the sample, using a quasi-planar THz wave with a beam diameter significantly larger than the sample dimensions.

Microwave and terahertz wave sensing with metamaterials.

We have designed, fabricated, and characterized metamaterial enhanced bimaterial cantilever pixels for far-infrared detection. Local heating due to absorption from split ring resonators (SRRs) incorporated directly onto the cantilever pixels leads to mechanical deflection which is readily detected with visible light. Highly responsive pixels have been fabricated for detection at 95 GHz and 693 GHz, demonstrating the frequency agility of our technique.

Stand-up magnetic metamaterials at terahertz frequencies.

We present a detailed study of non-planar or 'stand-up' split ring resonators operating at terahertz frequencies. Based on a facile multilayer electroplating fabrication, this technique can create large area split ring resonators on both rigid substrates and conformally compliant structures. In agreement with simulation results, the characterization of these metamaterials shows a strong response induced purely by the magnetic field.

High speed terahertz modulation from metamaterials with embedded high electron mobility transistors.

We present a computational and experimental study of a novel terahertz (THz) device resulting from hybridization of metamaterials with pseudomorphic high electron mobility transistors (HEMTs), fabricated in a commercial gallium arsenide (GaAs) process. Monolithic integration of transistors into each unit cell permits modulation at the metamaterial resonant frequency of 0.46 THz.

Comparison of birefringent electric split-ring resonator and meanderline structures as quarter-wave plates at terahertz frequencies.

We have fabricated a quarter-wave plate from a single layer of birefringent electric split-ring resonators (ELC). For comparison, an appropriately scaled double layer meanderline structure was fabricated. At the design frequency of 639 GHz, the ELC structure achieves 99.