Abstract-Superconducting emitters of THz radiation

                                                           The layered crystal structure of Bi₂Sr₂CaCu₂O_8+δ consists
                                                            of superconducting CuO₂ bilayers and intervening insulating
                                                            Bi–Sr–O layers, forming a stack of IJJs. The shaded background
                                                            represents the magnitude of the superconducting order

Ulrich Welp,¹ Kazuo Kadowaki², Reinhold Kleiner³
http://www.nature.com/nphoton/journal/v7/n9/full/nphoton.2013.216.html

Layered superconductors such as the copper-oxide high-temperature superconductor Bi₂Sr₂CaCu₂O_8+δ are emerging as compact sources of coherent continuous-wave electromagnetic radiation in the subterahertz and terahertz frequency ranges. The basis of their operation is the Josephson effect, which intrinsically occurs between the superconducting layers. The Josephson effect naturally converts a direct-current voltage into a high-frequency electric current. Therefore, a unique property of the devices reviewed here is the wide tunability of their frequency by varying the bias voltage. Recently, emission powers of free-space radiation of several hundreds of microwatts and emission linewidths as low as 6 MHz at 600 GHz have been achieved. These devices are promising for new applications in imaging, medical diagnostics, spectroscopy and security