We study the universal relationship between the hot-spot size and the intensity of terahertz emission from intrinsic Josephson junctions by dynamically controlling the temperature distributions in mesas of Bi 2 Sr 2 CaCu 2 O 8þδ . The uniform current bias leads to a significant increase in local temperature compared to the nonuniform current bias. The thermal response of emission differs between the high-and low-bias regimes. We find a strong positive correlation between the emission intensity and the volume of the superconducting parts in the emitting stack. We identify the remarkable increase in the emission intensity by up to 20% by eliminating the excess Joule heat from the mesa.

We propose an approach to control the polarization of terahertz (THz) radiation from intrinsic Josephsonjunction stacks in single crystalline high-temperature superconductor Bi2Sr2CaCu2O8. Monolithic control of the surface high-frequency current distributions in the truncated square mesa structure allows us to modulate the polarization of the emitted THz wave as a result of two orthogonal fundamental modes excited inside the mesa. Highly polarized circular terahertz waves with a degree of circular polarization of more than 99% can be generated using an electrically controlled method. The intuitive results obtained from the numerical simulation based on the conventional antenna theory are consistent with the observed emission characteristics.

We report emissions of circular polarized electromagnetic waves from cylindrically shaped mesa structures of the high-temperature superconductor Bi2Sr2CaCu2O8+δ. The frequency range of circularly polarized emission of a cylindrical mesa with notched sides is between 400 and 430 GHz, which is wider than expected by the patch antenna theory. Three maxima recognized in emission intensity are presumably attributed to excitations of fundamental orthogonal modes and circularly polarized modes. Along with the demonstration of circularly polarized emission from truncated edge square mesas, the obtained results provide a wide variety of engineering designs of compact and solid-state electromagnetic sources which are able to generate circularly-polarized terahertz waves.

We observe continuous terahertz-wave emission from a stack of intrinsic Josephson junctions made of slightly Pb-doped Bi 2 Sr 2 CaCu 2 O 8 d + . We investigate how Pb doping affects the c-axis current-voltage and emission characteristics. The terahertz emission spectra are measured by Fourier-transform infrared spectroscopy and reveal that the emission frequency is remarkably increased by Pb doping, an effect that we attribute to cavity resonance.

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