Research into generating terahertz (THz) radiation from the superconductor Bi2Sr2CaCu2O8+δ (Bi2212) has received attention recently, with the aim of creating a new compact THz light source. However, strong Joule heating associated with the large current flowing through the devices has hampered efforts. Now, T. Kitamura and co-workers from Japan and the USA have developed a stand-alone mesa fabrication procedure that greatly improves the thermal contact of the Bi2212 mesa with a surrounding thermal bath and thus allows the emission of high-power, continuous, broadly tunable THz radiation from 0.29 to 1.06 THz. The Bi2212 rectangular mesa with a 74 μm top width, 84 μm bottom width, 290 μm length and 2 μm thickness was fabricated using standard metal masks and Ar ion milling. The top and bottom surfaces were coated with Ti/Ag/Au metal layers and fixed to a sapphire substrate. As the temperature of the device increased from 10 K, the power of the output THz radiation gradually increased and then suddenly jumped up at a temperature of 54 K, peaked at 56 K and then decreased sharply above 70 K. The maximum power of the device was estimated to be about 20 μW. A radiation frequency of 1.06 THz was observed around 10 K, whereas a frequency of 0.29 THz was observed around 70 K.
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Horiuchi, N. Superconducting emitter. Nature Photon 9, 75 (2015). https://doi.org/10.1038/nphoton.2015.16
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DOI: https://doi.org/10.1038/nphoton.2015.16