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In this work the least squares method is used to reduce the anisotropy in transformation optics. To apply the least squares method we added power series on the coordinate transformation functions whose coefficients were calculated to reduce the deviations in Cauchy-Riemann equations. This technique does not violate boundary conditions necessary to avoid reflections on the borders and the functionality...
Terahertz ellipsometric and polarimetric measurement systems have been commissioned with the Novosibirsk free electron laser (FEL) being a source of monochromatic radiation. Calibration experiments with semiconductors and metamaterials showed correct operation of these systems. Blood films, monosaccharide, amino acids, and culture medium were studied.
We report on the terahertz analysis of the internal structure of ultra-high molecular weight polyethylene composite materials. The visualisation of interfaces between the perpendicularly arranged plies and the identification of stacking faults is possible because the THz refractive index depends on the orientation of fibres in the plies. Thicknesses of all plies in a composite material were determined...
We report the observation of negative group delay in a simple anisotropic cylindrical waveguide in the millimeter-wave region. With a 45° linearly polarized input, a relatively broad band of negative group delay was observed with 3.57% bandwidth, where the maximum group advancement achieved was about 24 times greater than the luminal delay, implying a fractional advancement of 13.32%. The peak advancement...
A new technique for the analysis and attenuation calculation of sub-millimeter waveguides is proposed in this paper by dividing the domain into several slices, in which the propagation constant ß and impedance Z for each slice were calculated and then used to estimate the overall attenuation as well as the reflection and transmission coefficients. Variations of losses with the waveguide dimensions,...
Spatially different arrangements of identical metaatoms in a unit cell bring about distinct properties in stereometamaterials. Integrating the stereometamaterial into a perfect metamaterial absorber, we designed, fabricated, and characterized a device with single or double band absorption responses and an absorption/reflection switching characteristic dependent upon the polarization of the incident...
A broadband terahertz reflective linear polarization convertor is proposed. The structure is composed of a metallic disk and split-ring resonators in proximity to a ground plane. It is found that the structure exhibits three neighboring resonances, from which the linear polarization of incident light can be rotated to its orthogonal counterpart after reflection. Both simulated and experimental results...
Surface plasmon polaritons at the n-GaN/vacuum interface are investigated. Experimental studies of terahertz radiation reflection and emission are performed on heavily silicon-doped GaN epitaxial layers grown on sapphire substrates. To provide interaction of THz radiation with the surface plasmon polaritons, a regular grating was fabricated on the outer surface of the epitaxial layer. Study of terahertz...
Reflection phase gratings offer great potential as local oscillator beam multiplexers in THz imaging heterodyne receivers. Using the Lagrange's multipliers method, we have optimized the phase profiles to achieve high diffraction efficiencies for three, four and five beam linear multiplexers. Experimental results at 2.5 THz are reported for a three-beam bulk aluminum multiplexing device.
An investigation of the terahertz properties of x-ray blocking and scattering (XBS) coating materials is performed. Spectral characterizations of the XBS materials reveal much stronger absorption coefficients as compared to the control coatings, as well as significant change in the refractive index. To examine the effectiveness of the coating material, pulsed THz reflection images of coated electronic...
We report the use of axicons to achieve broadband "focus-free" imaging in transmission and reflection at terahertz wavelengths. We demonstrate how the use of a broadband terahertz source improves the resolution of the imaging system, and how by using time-of-flight data the axial position and dimension of objects within the large depth of field of the axicon (160 mm) could be determined.
We investigate the THz response of human brain tissue exhibiting Alzheimer's disease. Amyloid plaque buildup, believed to be a possible cause of this disease, is typically diagnosed by immunohistochemical inspection of beta-amyloid in ex vivo biopsy specimens. Using a broadband THz time domain spectrometer system in reflection mode imaging, we demonstrate the possibility of discriminating between...
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