1,069 research outputs found

    Optical Diagnostics of Plasma Waves

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    Discovery of Bragg confined hybrid modes with high Q-factor in a hollow dielectric resonator

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    The authors report on observation of Bragg confined mode in a hollow cylindrical dielectric cavity. A resonance was observed at 13.4 GHzGHz with an unloaded Q-factor of order 2Ă—1052\times10^5, which is more than a factor of 6 above the dielectric loss limit. Previously such modes have only been realized from pure Transverse Electric modes with no azimuthal variations and only the EĎ•E_{\phi} component. From rigorous numeric simulations it is shown that the mode is a hybrid mode with non-zero azimuthal variations and with dominant ErE_r and EĎ•E_{\phi} electric field components and HzH_z magnetic field component.Comment: Accepted to be published in Applied Physics Letter

    An Experimental Examination of Spatial DecisionSupport System Effectiveness: The Roles of Task Complexity and Technology

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    Alaboratory experiment was used to investigate the effects on decision maker performance of using geographic information system (GIS) technology as a spatial decision support system (SDSS). The research examined two independent variables: task complexity (i.e., low, medium, and high complexity, and SDSS use (i.e., no SDSS versus SDSS support). Professionals who are experienced decision makers completed a site location task that required decisions to be made based upon spatially-referenced information. The results confirm the hypotheses and show that SDSS use and task complexity both have an important impact on decision quality and solution time. The study builds upon and extends image theory as a basis for explaining efficiency differences resulting from differing graphical displays of spatial informatio

    Detrapping and retrapping of free carriers in nominally pure single crystal GaP, GaAs and 4H-SiC semiconductors under light illumination at cryogenic temperatures

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    We report on extremely sensitive measurements of changes in the microwave properties of high purity non-intentionally-doped single-crystal semiconductor samples of gallium phosphide, gallium arsenide and 4H-silicon carbide when illuminated with light of different wavelengths at cryogenic temperatures. Whispering gallery modes were excited in the semiconductors whilst they were cooled on the coldfinger of a single-stage cryocooler and their frequencies and Q-factors measured under light and dark conditions. With these materials, the whispering gallery mode technique is able to resolve changes of a few parts per million in the permittivity and the microwave losses as compared with those measured in darkness. A phenomenological model is proposed to explain the observed changes, which result not from direct valence to conduction band transitions but from detrapping and retrapping of carriers from impurity/defect sites with ionization energies that lay in the semiconductor band gap. Detrapping and retrapping relaxation times have been evaluated from comparison with measured data.Comment: 7 pages, 6 figure

    Modified permittivity observed in bulk Gallium Arsenide and Gallium Phosphide samples at 50 K using the Whispering Gallery mode method

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    Whispering Gallery modes in bulk cylindrical Gallium Arsenide and Gallium Phosphide samples have been examined both in darkness and under white light at 50 K. In both samples we observed change in permittivity under light and dark conditions. This results from a change in the polarization state of the semiconductor, which is consistent with a free electron-hole creation/recombination process. The permittivity of the semiconductor is modified by free photocarriers in the surface layers of the sample which is the region sampled by Whispering Gallery modes.Comment: 8 pages, 3 figure

    Towards achieving strong coupling in 3D-cavity with solid state spin resonance

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    We investigate the microwave magnetic field confinement in several microwave 3D-cavities, using 3D finite-element analysis to determine the best design and achieve strong coupling between microwave resonant cavity photons and solid state spins. Specifically, we design cavities for achieving strong coupling of electromagnetic modes with an ensemble of nitrogen vacancy (NV) defects in diamond. We report here a novel and practical cavity design with a magnetic filling factor of up to 4 times (2 times higher collective coupling) than previously achieved using 1D superconducting cavities with small mode volume. In addition, we show that by using a double-split resonator cavity, it is possible to achieve up to 200 times better cooperative factor than the currently demonstrated with NV in diamond. These designs open up further opportunities for studying strong and ultra-strong coupling effects on spins in solids using alternative systems with a wider range of design parameters.Comment: 20 pages, 9 figure

    Phase diagram of silicon from atomistic simulations

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    In this letter we present a calculation of the temperature-pressure phase diagram of Si in a range of pressures covering from -5 to 20 GPa and temperatures up to the melting point. The phase boundaries and triple points between the diamond, liquid, β\beta-Sn and Si34{Si}_{34} clathrate phases are reported. We have employed efficient simulation techniques to calculate free energies and to numerically integrate the Clausius-Clapeyron equation, combined with a tight binding model capable of an accuracy comparable to that of first-principles methods. The resulting phase diagram agrees well with the available experimental data.Comment: 5 pages, 1 figure, accepted in PR
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