Impedance matching and heat management are important factors influencing the performance of terahertz sources. In this work we analyze thermal and radiative properties of such devices based on mesa structures of a layered high-temperature superconductor Bi2Sr2CaCu2O8+δ. Two types of devices are considered containing either a conventional large single crystal or a whisker. We perform numerical simulations for various geometrical configurations and parameters and make a comparison with experimental data for the two types of devices. It is demonstrated that the structure and the geometry of both the superconductor and the electrodes play important roles. In crystal-based devices an overlap between the crystal and the electrode leads to appearance of a large parasitic capacitance, which shunts terahertz emission and prevents impedance matching with open space. The overlap is avoided in whisker-based devices. Furthermore, the whisker and the electrodes form a turnstile (crossed-dipole) antenna facilitating good impedance matching. This leads to more than an order of magnitude enhancement of the radiation power efficiency in whisker-based, compared to crystal-based, devices. These results are in good agreement with presented experimental data.

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Impedance matching and heat management are important factors influencing performance of THz sources. In this work we analyze thermal and radiative properties of such devices based on mesa structures of a layered high-temperature superconductor Bi2Sr2CaCu2O8+δ. Two types of devices are considered, containing either a conventional large single crystal, or a whisker. We perform numerical simulations for various geometrical configurations and parameters and make a comparison with experimental data for the two types of devices. It is demonstrated that the structure and the geometry of both the superconductor and the electrodes are playing important roles. In crystal-based devices an overlap between the crystal and the electrode leads to appearance of a large parasitic capacitance, which shunts THz emission and prevents impedance matching with open space. The overlap is avoided in whisker-based devices. Furthermore, the whisker and the electrodes form a turnstile (crossed-dipole) antenna facilitating good impedance matching. This leads to more than an order of magnitude enhancement of the radiation power efficiency in whisker-based, compared to crystal-based devices. These results are in good agreement with presented experimental data.

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Жуков В.Т., Краснов М.М., Новикова Н.Д., Феодоритова О.Б. Алгебраический многосеточный метод c адаптивными сглаживателями на основе многочленов Чебышева Для численного решения трехмерных эллиптических уравнений построен адаптивный алгебраический многосеточный метод (АММ). Новым элементом является объединение техники АММ с потенциалом сглаживателей на основе оптимальных многочленов Чебышева. Показаны возможности автоматической адаптации сглаживателей к границам дискретных операторов. Обсуждаются свойства двух сглаживателей чебышевского типа -полинома и рациональной функции; приводятся результаты экспериментальной проверки АММ. Эффективная реализация сглаживателей и процедуры решения уравнений на самом грубом дискретном уровне с помощью явно-итерационных чебышевских алгоритмов обеспечивает возможность функционирования параллельного кода на современных суперкомпьютерных архитектурах. We introduce an adaptive algebraic multigrid method (AMG) for numerical solution of three-dimensional elliptic equations. A new element is the integration of AMG technique with the smoothers based on optimal Chebyshev polynomials. The possibilities of automatic adaptation of smoothers to the bounds of the АMG discrete operators are shown. The properties of two smoothers, the polynomial and the rational function, are discussed. The results of experimental verification of the AMG are given. Effective implementation of the smoothers and solver for the coarsest equations with the help of Chebyshev explicit-iterative algorithms enables the functioning of the parallel code on modern supercomputer architectures.Key words: elliptic equations, algebraic multigrid method, Chebyshev polynomials, adaptive smoother Работа выполнена при финансовой поддержке Российского научного фонда (проект № 14-21-00025)