Recent advances in the fabrication, performance and application of superconducting sources of THz-radiation.

Electromagnetic radiation in the THz-frequency range is attracting increased interest due to a wide range of potential applications in medical diagnostics, high-bandwidth communication, security and defense, nondestructive evaluation, spectroscopy and other fields. In general, these applications would benefit from compact sources of continuous wave radiation. Here, I will review recent progress in superconducting sources of THz-radiation whose operation is based on the Josephson effect. Two successful approaches have emerged: a) Flux Flow Oscillators (FFO) based on artificial Niobium or Niobium nitride Josephson junctions that have been deployed as local oscillators and operate at frequencies in excess of 600 GHz, b) stacks of so-called Intrinsic Josephson junctions (IJJ) in highly-layered high-temperature superconductors such as Bi₂Sr₂CaCu₂O_8-d. In the latter, the synchronization of a large number of IJJ by means of a cavity resonance enables emission powers of 0.6 mW. Emission frequencies approaching 2 THz and operation at temperatures above 77 K have been achieved. Applications in imaging and spectroscopy have successfully been demonstrated. Finally, I will describe ongoing efforts in device packaging, heat management and attempts to fabricate devices on epitaxial Bi₂Sr₂CaCu₂O_8-d films.