Radio physics and electronics

15-36

Authors: A. А. Barannik, A.І. Gubin, A. А. Lavrinovich, N. T. Cherpak

The subject and purpose of the work. A review of the main results obtained by the authors in the process of microwave (MW) research of unconventional superconductors and the development of MW devices based on cuprate high-temperature superconductors (HTS) over the past 10–15 years is presented. Methods and methodology of work. Experimental studies were carried out by the methods of impedance measurements of superconducting samples. To this end, the authors developed two measurement techniques in the mm wavelength range: based on quasi-optical sapphire resonators and using the feature of reflection of a p-polarized wave from the surface of a superconductor at grazing angles of incidence. The results of the work.. The epitaxial films of the cuprate YBa2Cu3O7–d superconductor and Fe-containing superconductors in the form of single crystals of pnictide Ba (Fe0.926Co0.074)2As2 and epitaxial films of chalcogenide FeSexTe1–x (x = 0.5 and 0.7) are investigated. The results of the MW response of the electrodynamic structures with the samples under study served as the basis for finding the complex conductivity, including fluctuation one, and physical quantities related to it. In general, the results obtained confirm the scenario of d-wave symmetry of the gap function for cuprate superconductors and s±-wave symmetry for Fe superconductors. However, a number of detected features and effects, namely, an unusual frequency dependence of the residual surface resistance in YBa2Cu3O7–d in the form of w3./2, the growth of quasiparticle conductivity with decreasing temperature, starting from the critical one, as well as the avalanche-like transition from the superconducting to the strongly dissipative state in the nonlinear coplanar transmission line, require further study. New MW devices based on cuprate HTS films in the mm wavelength range have been developed and created: 1) a quasi-optical sapphire resonator with a radial gap and HTS end walls for studying Fe – superconductors in the form of small (1–2 mm in the plane a–b) samples; 2) planar quasi-optical resonator; 3) a band-pass filter with an E-plane insert in a cross-shaped waveguide. The possibility of contactless testing at room temperature of the homogeneity of the properties of massive superconductors is also shown. Conclusion. The temperature dependence of the complex conductivity of YBa2Cu3O7–d, Ba (Fe0.926Co0.074)2As2 and FeSexTe1–x (x = 0.5 and 0.7) superconductors and physical quantities related with it was obtained, which allows us to judge the confirmation of the corresponding wave symmetry scenarios of gap function function in the investigated superconductors. However, a number of detected features and effects require further study. The previously expressed assessment of the possibility of creating passive HTS-based MW devices with operating frequencies up to 40 GHz has been experimentally confirmed.

55-66

Authors: S. S. Apostolov, D. V. Kadygrob, Z. A.Маizelis, T. N. Rokhmanova, A. A. Shmat’ko, V. A. Yampol’skii

Subject and purpose. In this review the propagation of electromagnetic waves localized near the boundary of a sample of a layered superconductor with layers either parallel or perpendicular to its surface is discussed. The results obtained in a number of papers studying the dispersion law for such waves are generalized, classified and supplemented. Due to the strong anisotropy and nonlinearity of the Josephson plasma in layered superconductors, localized waves can have unusual dispersion properties, and their excitation can be accompanied by unusual resonance phenomena. Methods and methodology. The electromagnetic field in a layered superconductor is determined by the distribution of the gauge-invariant phase difference of the order parameter, which satisfies the system of coupled sin-Gordon equations. Based on the solution of these equations, as well as the Maxwell equations in the dielectric environment, dispersion relations can be obtained for localized electromagnetic modes. Results. In samples of a layered superconductor, whose layers are parallel to its boundary, both surface waves and waveguide modes with normal dispersion can propagate. For samples, the layers in which are perpendicular to the boundary, the dispersion law depends on the angle of propagation of the waves relative to the superconducting layers. In this paper it is shown for the first time that waves localized in a layered superconductor plate have an anomalous dispersion for all directions of propagation, except propagation strictly along the layers. Dispersion curves for such waves can have points of maximum and/or minimum, which can lead to nontrivial effects (e.g., stopping of light or internal reflection). Also, the excitation of localized waves and the unusual resonant phenomena are discussed in the work. Conclusions. Due to the strong anisotropy and nonlinearity of the layered superconductor, the dispersion laws for waves, localized both in semi-infinite samples and in plates have a number of interesting features that lead to new phenomena important for using in the physics of the terahertz range.

95-107

Authors: S.V.Nikolaev, V.V.Pozhar, M.I.Dzyubenko, K.S. Nikolayev

Subject and purpose. This article is devoted to a brief review of the main results of the research cycle aimed at developing solid active media based on dye-activated polyurethane compounds. The ultimate goal of these studies was the creation of solid-state active elements that make it possible to realize a wide-band solid-state dye laser (SSDL), which emits frequency-tunable radiation with a microsecond pulse duration. Methods and methodology. The problem was solved mainly by experimental methods. At the same time, the studies carried out included a full range of works, starting with the production of samples of solid-state active media to study the generation characteristics of the active elements created. Results. In the course of the work, laser-active media based on industrial polyurethanes of various grades activated with Rhodamin 6G, Sulforhodamine 101, Oxazin 17, and Oxazin 1 dyes have been created and their spectral-luminescent characteristics have been studied. Experimental samples of laser matrices are made. The optical properties of the media created are studied and the influence of the technique of making samples on the nature of possible distortions of their optical homogeneity is determined. The emission ability of polyurethane matrices was studied. With transverse monochromatic excitation laser emission was obtained on polyurethane matrices with an efficiency of 12 to 26% and energies from 23 to 127 mJ. Radiation resistance and possible service life of polyurethane media have been investigated The thermo-optical properties of polyurethane active media and their effect on the directivity of SSDL radiation are studied. The effect of induced birefringence, which occurs under conditions of asymmetric pumping of microsecond duration, is observed. It was found that under such conditions, polyurethane active elements emits polarized radiation even when excited by depolarized light. A possibilities of narrowing and tuning the emission spectrum of polyurethane matrices in dispersion resonators with angular and amplitude type of selection are investigated. The laboratory model of a tunable SSDL with replaceable polyurethane laser elements, generating a pulsed radiation of a microsecond duration in the spectral range of 565...700 nm is created and tested. Conclusions. The results of the performed studies allow to conclude that industrial polyurethane compounds can be successfully used as solid media for active elements of SSDL.