Comparison of luminescent and scanning laser thermal micro-imaging of self-heating in Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8}$ mesa THz sources*

Scanning laser thermal microscopy of stacked Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8}$ Josephson junction terahertz sources has revealed both electromagnetic cavity resonance modes and strongly non-uniform self-heating in these devices. However, this technique -- in which a modulated laser beam is rastered across the surface of a device -- excites a number of physical phenomena, and thus the resulting images can be difficult to interpret. Here we compare scanning laser images taken on Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8}$ mesa THz sources with micro-images collected via a thermoluminescent technique under identical conditions. The latter technique directly measures the device surface temperature, and we find excellent agreement with the scanning laser results, confirming that scanning laser thermal microscopy is indeed primarily probing device temperature.