Terahertz imaging of sub-wavelength particles with Zenneck surface waves

Impact of sub-wavelength-size dielectric particles on Zenneck surface waves on planar metallic antennas is investigated at terahertz (THz) frequencies with THz near-field probe microscopy. Perturbations of the surface waves show the particle presence, despite its sub-wavelength size. The experimental configuration, which utilizes excitation of surface waves at metallic edges, is suitable for THz imaging of dielectric sub-wavelength size objects. As a proof of concept, the effects of a small strontium titanate rectangular particle and a titanium dioxide sphere on the surface field of a bow-tie antenna are experimentally detected and verified using full-wave simulations

Low-temperature electronic heat transport in La_{2-x}Sr_{x}CuO_{4} single crystals: Unusual low-energy physics in the normal and superconducting states

The thermal conductivity \kappa is measured in a series of La_{2-x}Sr_{x}CuO_{4} (x = 0 - 0.22) single crystals down to 90 mK to elucidate the evolution of the residual electronic thermal conductivity \kappa_{res}, which probes the extended quasiparticle states in the d-wave gap. We found that \kappa_{res}/T grows smoothly, except for a 1/8 anomaly, above x = 0.05 and shows no discontinuity at optimum doping, indicating that the behavior of \kappa_{res}/T is not governed by the metal-insulator crossover in the normal state; as a result, \kappa_{res}/T is much larger than what the normal-state resistivity would suggest in the underdoped region, which highlights the peculiarities in the low-energy physics in the cuprates.Comment: 5 pages, 3 figures, final version published in PRL. Discussions have been modified and an analysis of the phonon term has been adde

Near-field probing of the THz Mie magnetic mode in a single sub-wavelength TiO2 sphere

We report the first investigation of single Titanium Dioxide (TiO2) sub-wavelength size (20-30μm) spheres and ellipsoids using THz near-field microscopy. The Mie resonances are observed in individual particles allowing characterization of the resonance line-width and its dependence on the particle dimensions and shape

THz response of TiO2 microspheres embedded in a dielectric layer

TiO2 microspheres embedded in a dielectric layer were investigated both experimentally using time domain terahertz (THz) spectroscopy, and theoretically by finite-difference time-domain method. We focus on the role of the permittivity of the embedding medium. We find that media with sufficiently low permittivities do not significantly affect the effective response of the microspheres, which is a prerequisite for the fabrication of durable metamaterials with fixed spatial distribution of the components

Strong suppression of In desorption from InGaN QW by improved technology of upper InGaN/GaN QW interface

International audienceThe aim of this work is to elucidate how different growth mode and composition of barriers can influence the QW properties and their PL and to find optimal QW capping process, to suppress the In desorption from QWs and to maintain the QW PL efficiency. It concentrates on the technology procedure for growth of upper quantum well (QW) interfaces in InGaN/GaN QW structure when different temperature for QW and barrier epitaxy is used. We have found that optimal photoluminescence (PL) results were achieved, when the growth after QW formation was not interrupted, but immediately continued during the temperature ramp by the growth of (In)GaN capping layer with small introduction of In precursor into the reactor. Optimal barrier between QW with respect to PL results was found to be pure GaN. We have shown according to SIMS and HRTEM results that by this technological procedure the InGaN desorption was considerably suppressed and three times higher In concentration and two times thicker QWs were achieved for the same QW growth parameters without deterioration of PL intensity in comparison to sample with usually used thin GaN low temperature capping protection. Additionally, for samples covered by the QW capping layer during the temperature ramp the defect band is almost completely missing, thus we can conclude that this defect band is connected with quality of the upper QW interface

Near-field spectroscopy of sub-wavelength (<λ/10) anisotropic dielectric resonators at terahertz frequencies

International audienc

Zenneck THz Surface Waves-assisted Imaging of Subwavelength Dielectric Particles

Electromagnetic Zenneck THz surface waves propagating on a bow-tie antenna are employed for time-resolved near-field imaging of subwavelength-size SrTiO3 and TiO2 particles. This approach provides high contrast, high-spatial resolution imaging through enhancing the fieldparticle interaction

Surface plasmon waves for broadband THz spectroscopy

In this presentation we discuss application of broadband terahertz (THz) time-domain spectroscopy for probing subwavelength (micrometer) size objects. The problem of weak coupling between THz waves and sub-wavelength objects, which limits the use of THz spectroscopy to large samples, is mitigated by employing surface plasmon waves. In one implementation, THz surface waves, excited on a broad-band planar THz bow-tie antenna, are used to enhance the interaction with a small particle placed on the antenna surface. The surface field distribution near the particle is mapped with an integrated sub-wavelength aperture THz near-field probe. We demonstrate that imaging and probing of the subwavelength size dielectric particles (TiO2 and SrTiO3) can be realized using the enhanced THz field between the antenna and the probe. We also discuss THz wave confinement using two sharp metallic needles. We demonstrate that in the near-field region of the needle tips, the electric field of THz pulses is concentrated to a volume smaller than (10 &mu;m)3 without limiting the THz pulse bandwidth. Application of both methods for high spatial resolution imaging and spectroscopy will be discussed