The radiation intensity from the intrinsic Josephson junction high-T_c superconductor Bi₂Sr₂CaCu₂O_8+δ terahertz emitters (Bi2212-THz emitters) is one of the most important characteristics for application uses of the device. In principle, it would be expected to be improved with increasing the number of intrinsic Josephson junctions N in the emitters. In order to further improve the device characteristics, we have developed a stand alone type of mesa structures (SAMs) of Bi2212 crystals. Here, we understood the radiation characteristics of our SAMs more deeply, after we studied the radiation characteristics from three SAMs (S1, S2, and S3) with different thicknesses. Compar-ing radiation characteristics of the SAMs in which the number of intrinsic Josephson junctions are N ∼ 1300 (S1), 2300 (S2), and 3100 (S3), respectively, the radiation intensity, frequency as well as the characteristics of the device working bath temperature are well understood. The strongest radiation of the order of few tens of microwatt was observed from the thickest SAM of S3. We discussed this feature through the N²-relationship and the radiation efficiency of a patch antenna. The thinner SAM of S1 can generate higher radiation frequencies than the thicker one of S3 due to the difference of the applied voltage per junctions limited by the heat-removal performance of the device structures. The observed features in this study are worthwhile designing Bi2212-THz emitters with better emission characteristics for many applications.

We discuss the cavity modes and radiation pattern in solid state terahertz (THz) sources based on layered high-temperature superconducting Bi ₂ Sr ₂ CaCu ₂ O _8+δ (Bi-2212). We experimentally measure the emission spectra using the Fourier transform infrared spectrometer in order to elucidate the radiation mechanism of the mesa samples. Moreover, we experimentally study the angular dependence of the emission intensity obtained in one mesa's plane at the frequency f = 0.61 THz, at various detection angles θ by rotating the sample holder relative to the detector, to identify the excited EM cavity modes within the mesa that participate in the device output power enhancement. We modelled the mesa cavity and find a relatively good agreement between the experiment and theory. Our results show that compact, coherent and continuous-wave Bi-2212 THz devices are one of the most promising THz sources, capable of bridging the microwaves to photonics gap.

Since the discovery of continuous, coherent THz radiation from intrinsic Josephson junctions (IJJs) constructed in the single crystals of Bi₂Sr₂CaCu₂O_8+δ in 2007, various types of device structures have been developed. Thermal management of Joule heat in the IJJ mesa structure is the most important issue to improve the radiation characteristics of the IJJ-THz emitters. The radiation frequencies ranging from 0.3 to 2.4 THz, the emission power of $ \sim 30$ pW/mesa and the radiation linewidth of 0.2 GHz at $ \sim 0.5$ THz were obtained from the thermal managed device structures so far. We show a brief overview of the IJJ-THz emitters in our group.