Self-Mixing Spectra of Terahertz Emitters Based on Bi2Sr2CaCu2O8+δ Intrinsic Josephson-Junction Stacks

Developing technology to exploit the ``THz window'' of the electromagnetic spectrum continues to be a major research theme. Stacks of intrinsic Josephson junctions in a cuprate superconductor are a good source of THz photons; with them, one can even imagine a THz laser on a chip. To better understand the purity of this radiation, the authors study the phenomenon of self-mixing, in which the nonlinearity of the Josephson elements leads to two or more nearby THz emission peaks producing signals at the difference frequencies. These results are helpful for synchronizing thousands of Josephson junctions, and may offer a simple method for evaluating the coherence of their THz emission.