Study of Joule heating characteristics of Bi₂Sr₂CaCu₂O_8+δ high-<i>T</i>_c superconducting terahertz emitters

In order to understand the emission characteristics of Bi₂Sr₂CaCu₂O_8+δ (Bi2212) high-T_c superconducting THz emitters, it is very important to clarify the Joule heating characteristics of the devices. Recently, in order to reduce the self-heating from the Bi2212-THz emitters, we have proposed a stand-alone mesa structure of Bi2212 single crystals and its sandwich structures. The radiation characteristics obtained from these devices indicate clearly that the thermal management of the THz emitters is most important issue in order to obtain good radiation performance and reproducibility.
In order to optimize the thermal management design of the devices, temperature evaluation techniques of the mesa devices would serve an essential tool. Visualization studies of the Joule heat in the mesa devices have been well performed with various techniques. Recently, instead of those methods, we proposed to use thermoreflectance microscopy (TRM) technique. This TRM method is a non-contact thermal imaging technique with sub-micron spatial resolution, and can provide us more important characteristics of the intrinsic temperature of the surface without any special treatment of the surface of the mesa devices. The measurement technique and the advantages of the TRM method will be discussed.