We present an experimental approach allowing the evaluation of the effective dielectric permittivity and magnetic
permeability of metamaterials from measurements by time-domain terahertz spectroscopy. A resonant magnetic response of TiO2 dielectric microspheres was observed in the THz range, showing that negative effective permeability can be achieved in this way. Numerical simulations explain the observed behavior, and show that by
combining the microspheres with a metallic mesh, a negative refractive index can be obtained.
Metamaterials are artificial materials with unusual properties that do not exist in nature and basically could consist of
subwavelength metallic patterns printed on dielectric substrate. In this paper, we present a theoretical and experimental
investigations of metamaterials designed for THz applications. First, fishnet metamaterials which are composed with a
thin dielectric material sandwiched between two metallic layers. Two techniques were used in order to fabricate our
prototypes: double layer optical lithography and laser micromachining. We performed simulations and experiments using
commercial software simulator based on finite element method (HFSS) and terahertz time domain spectroscopy THz-
TDS respectively. A good agreement was reported between simulations and experiments while pointed out the dramatic
influences of dielectric losses in the effective response.
We report on recent measurements and analysis performed with a metal-dielectric near-field terahertz probe. The images obtained with the near-field probe have been decomposed using factor analysis. Components corresponding to the dielectric properties of investigated samples and to the distance of the probe and of the sample have been identified. We further employed the probe for investigation of local anisotropy in a BaTiO3 crystal.
In this work we report on structures operating as actively tunable filters or modulators for the terahertz spectral
range. These devices can be described as one-dimensional photonic crystals with defects and are composed
of quartz, MgO and GaAs thin platelets; the optically transparent materials (quartz and MgO) are used as
Bragg mirrors forming a resonator and GaAs is placed inside this resonator. The tunability is achieved by
photoexcitation of free carriers within the GaAs layer by an ultrashort laser pulse. The optical control of
such devices features a very fast (sub-nanosecond) response which is attractive e.g. for future applications in
telecommunications.
We report on optical rectification at bulk and thin film noble metal (Ag and Au) surfaces investigated by means of terahertz time-domain spectroscopy. The experimental data are well modelled using a nonlinear surface susceptibility tensor. The main contribution comes from the charges moving along the surface normal. For gold films, the terahertz signal decreases dramatically for thicknesses below 150 nm. We tentatively explain this phenomenon by screening of the nonlinear polarization by the field induced by charges that have moved across the layer.
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