New Express Method for Measuring the Thermal Diffusivity of Non-Metallic Materials on an Example of Zirconium Ceramics

Russian Physics Journal -     

Millimeter-wave Hilbert-transform spectrum analyzer based on Josephson junction

Conclusions A prototype of the Hilbert-transform spectrum analyzer based on the Josephson junctions is described and first spectral measurements are demonstrated in millimeter-wave band. The measurements in the whole millimeter-wave band may be carried out by this spectrum analyzer with resolution as low as 2 GHz and during a time interval as low as a few milliseconds. According to this set of parameters, this Josephson-effect spectrum analyzer may be used for microwave diagnostics of the thermonuclear plasma.     

Ultrafast relaxation of excited Dirac fermions in epitaxial graphene using optical differential transmission spectroscopy

We investigate the ultrafast relaxation dynamics of hot Dirac fermionic quasiparticles in multilayer epitaxial graphene using ultrafast optical differential transmission spectroscopy. We observe differential transmission spectra which are well described by interband transitions with no electron-hole interaction. Following the initial thermalization and emission of high-energy phonons, the electron cooling is determined by electron-acoustic phonon scattering, found to occur on the time scale of 1 ps for highly doped layers, and 4-11 ps in undoped layers. The spectra also provide strong evidence for the multilayer structure and doping profile of thermally grown epitaxial graphene on SiC.     

Generation of radially polarized terahertz pulses via velocity-mismatched optical rectification

We demonstrate the generation of radially polarized terahertz pulses via optical rectification in a Cherenkov geometry exploiting velocity mismatch, contrary to the traditional approach for generating linearly polarized terahertz beams. A compact system is implemented using 001-cut ZnTe pumped by an ultrafast Yb-doped fiber amplifier.     

Copper vapor laser with intracavity radiation scanning by a spatial and temporal light modulator based on PLZT ceramics

The results of an experimental study of the output radiation parameters of a copper vapor laser (CVL) with a self-conjugate resonator are presented. TheQ-factor was controlled by diaphragms (slit or circular) and spatial and temporal light modulators (STLM) based on PLZT ceramics.     

Anisotropic distributions of electrical currents in high-<Emphasis Type="Italic">T</Emphasis><Subscript><Emphasis Type="Italic">c</Emphasis></Subscript> grain-boundary junctions

We developed a self-consistent method for the calculation of spatial current distributions in high-T _c grain-boundary junctions. It is found that crystallographic anisotropy of high-T _c superconducting electrodes results in the effects, which previously were not taken into account for interpretations of experimental data. Among them is a significant redistribution of electrical currents in superconducting electrodes in the vicinity of a grain boundary. In particular in the case of [100]-tilt bicrystal junctions, this current redistribution results in a substantial focusing to the top or bottom part of a thickness of the grain boundary, depending on “roof”- or “valley”-type of the grain boundary. This redistribution is accompanied by generation of vortex currents around the grain boundary, which leads to self-biasing of grain-boundary junctions by magnetic field nucleated by these vortex currents. It is shown that twinning or variation of geometrical shape of the high-T _c electrode may also result in intensive redistribution of electrical currents and nucleation of local magnetic fields inside a high-T _c superconducting electrodes.