We measured the optical absorption spectra of thermally treated, gamma irradiated LiF crystals, as a function of temperature in the range 16–300K. The temperature dependence of intensity, peak ...position and bandwidth of F and M absorption bands were obtained.
This paper reports the design, the microfabrication and the experimental characterization of an ultra-thin narrow-band metamaterial absorber at terahertz frequencies. The metamaterial device is ...composed of a highly flexible polyimide spacer included between a top electric ring resonator with a four-fold rotational symmetry and a bottom ground plane that avoids misalignment problems. Its performance has been experimentally demonstrated by a custom polarization-maintaining reflection-mode terahertz time-domain spectroscopy system properly designed in order to reach a collimated configuration of the terahertz beam. The dependence of the spectral characteristics of this metamaterial absorber has been evaluated on the azimuthal angle under oblique incidence. The obtained absorbance levels are comprised between 67% and 74% at 1.092 THz and the polarization insensitivity has been verified in transverse electric polarization. This offers potential prospects in terahertz imaging, in terahertz stealth technology, in substance identification, and in non-planar applications. The proposed compact experimental set-up can be applied to investigate arbitrary polarization-sensitive terahertz devices under oblique incidence, allowing for a wide reproducibility of the measurements.
A double-sided phase-reversal binary zone plate is numerically investigated and experimentally characterized at the frequency of 1 THz. The double-sided zone plate has a novel design based on a ...binary phase-reversal zone plate, in which the total zone thickness is split into two halves located at a distance optimized by means of numerical simulations. The samples are fabricated by a three-axis milling technique on slabs of an ultralow-loss cyclo-olefin polymer. The lenses' characterization at the frequency of 1 THz is performed by means of a terahertz time-domain spectrometer, in terms of both focal length and spatial resolution. The focusing properties of the double-sided zone plate are compared with those of a conventional binary zone plate. The double-sided zone plate features 2.4× smaller focal spot, 1.25× higher focusing efficiency, and an approximately 10λ 0 longer depth of field than the conventional binary configuration.
We propose a new broadband swept frequency technique to measure the complex resistivity of high T/sub c/ superconducting thin films in the microwave range (from a few GHz up to 50 GHz). A coaxial ...cable connects the sample to a vector network analyzer which performs reflection measurements; the film and the coaxial end are separated by a short section of circular waveguide. The absence of direct electrical contact between the sample and the coaxial core simplifies realization and avoids contact instability with large temperature variations. We provide an electromagnetic analysis of the coaxial to cylindrical transition (CCT) and find a closed form relation between the measured quantities and the film resistivity. Finally, we present some experimental results obtained for an YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// thin film using the described method.
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