Stacked Intrinsic Josephson Junction Bi2 Sr2 CaCu2 O8 Terahertz Sources: Design Issues for Achieving High Power Output Close to Tc

The high-temperature superconductor Bi
₂
Sr
₂
CaCu
₂
O
₈
contains stacked `intrinsic' Josephson junctions, with unrivaled packing density and a high superconducting gap energy. Cuboid `mesa' devices constructed from this material are consequently a promising technology for coherent, continuouswave radiation in the `terahertz gap' range, spanning from approximately 0.3-1.5 THz. A key issue for practical applications of such devices is their cryocooling requirements, and it is therefore highly desirable to optimize their performance at temperatures that can be achieved by nitrogen cryogenics. Here we report generation of 0.13 milliwatts of coherent emission power at 0.461 THz, at a bath temperature of 77.4 Kelvin. This was achieved by exciting the (3, 0) cavity mode of a stack containing 579 junctions, and with T
_c
of 86.5 Kelvin. In order to minimize selfheating, the THz source was mounted on a copper substrate using PbSn solder. We will discuss the choice of mesa dimensions and cavity mode, and implications for the design of devices which are intended to operate close to the material's superconducting critical temperature.