Terahertz thermal imaging of a cold object with a 4 K-cryocooled photoconductive detector

We have demonstrated terahertz (THz) passive imaging of a cold object using a 4 K-cryocooled THz photoconductive detector with BLIP at around 1.5-2.5 THz. In our imaging system, we achieved a resolution of 240 μm, a background limited NEP of 7.7×10^-15W/√Hz and a NETD of 11 mK. We have measured temperature dependence of THz intesity emitted from a sample with the emissivity of 0.99. The result shows that the THz intensity has a good linear relation to the temperature.