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21 results on '"Fastampa, Renato"'

4. Dynamic regimes in YBCO in applied magnetic field probed by swept frequency microwave measurements

Author

Sarti, Stefano, Giura, Maurizio, Fastampa, Renato, Silva, E, Amabile, C, Boffa, M, Cucolo, A. M., Sarti, S, Silva, Enrico, Giura, M, Fastampa, R, Boffa, M, and Cucolo, Am

Subjects
Condensed matter physics, Electrical resistivity and conductivity, Chemistry, Plane (geometry), Condensed Matter::Superconductivity, Continuum (design consultancy), General Materials Science, Dissipation, Condensed Matter Physics, Microwave, Line (formation), Vortex, Magnetic field
Abstract

We report measurements of the microwave resistivity in YBa2Cu3O7-delta (YBCO), in the presence of an applied magnetic field. Measurements are performed as a function of frequency, over a continuum spectrum between 6 and 20 GHz, by means of a Corbino disc geometry. These data allow for a direct identification of different dynamical regimes in the dissipation of YBCO in the presence of an applied magnetic field. While at high temperatures a frequency independent resistivity is observed, at lower temperatures we find a marked frequency dependence. The line in the (H, T) plane at which this change in the dynamical regime is observed is clearly identified and discussed in terms of vortex motion and fluctuational resistivity.

Published
2004

21. Terahertz focusing properties of polymeric zone plates characterized by a modified knife-edge technique

Author

Silvia Tofani, Renato Fastampa, Romeo Beccherelli, Dimitrios C. Zografopoulos, and Mauro Missori

Subjects
Materials science, Polymers, Terahertz radiation, Time domain analysis, Efficiency, Zone plate, Edge (geometry), Diffraction efficiency, 01 natural sciences, Electromagnetic radiation, law.invention, terahertz, 010309 optics, Optics, Stack (abstract data type), law, 0103 physical sciences, zone plate, Focusing, diffractive lenses, Parabolic reflector, business.industry, Statistical and Nonlinear Physics, Atomic and Molecular Physics, and Optics, Finite element method, Terahertz spectroscopy, Antennas, business
Abstract

The focusing properties of a series of polymeric zone-plate lenses are investigated around a target frequency of 1 THz. Their characterization is performed by means of terahertz (THz) time-domain spectroscopy, employing a modified knife-edge technique that compensates for asymmetries of the impinging THz beam shape of typical photoconductive antenna-based THz sources. The samples are fabricated by a three-axis milling technique on slabs of an ultralow-loss cyclo-olefin polymer. Three different zone plates are studied, a conventional binary zone plate, a conventional four-level zone plate, and a recently introduced double-sided zone plate consisting of the stack of two phase-reversal binary zone plates, which is simpler to fabricate and less sensitive to mechanical damage than multilevel zone plates. Experimental results, coupled with finite element simulations, demonstrate that the double-sided zone plate features a resolution increased by about 3 lambda with respect to the binary zone plate and comparable with that of the four-level zone plate. The double-sided zone plate has 40% lower focusing efficiency and approximately 7 lambda shorter depth of field compared to its four-level counterpart. Nevertheless, it outperforms conventional binary zone plates by 25% in power focusing efficiency and features a 10 lambda longer depth of field. (C) 2019 Optical Society of America

Published
2019
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