Characterization of cavity mode and radiation pattern in superconducting coherent terahertz emitters

We discuss the broadly tunable terahertz (THz) radiation in solid state terahertz (THz) emitters based on high-temperature superconducting Bi2Sr2CaCu2O8+δ (Bi-2212). We experimentally measure the current-voltage characteristics (IVC) of mesas of different geometries, such as triangular-, pentagonal-, hexagonal-, and elliptical- cavities, and compare the IVC of the radiating and no-radiating cavities. The THz emission spectra in radiating THz cavities was measured using the Fourier transform infrared spectrometer in order to elucidate the radiation mechanism of the emitters. Moreover, we experimentally and theoretically study the angular dependence of the emission intensity obtained in mesas’ plane at various frequencies and detection angles, by rotating the sample holder relative to the detector, to identify the excited EM cavity modes within the cavities that participate in the emitter output power enhancement.
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