Broadband high-absorbance coating for terahertz radiometry.

We report a simple, broadband and high-absorbance coating for terahertz radiometry. The spectral properties of this coating in THz region were characterized with a home-made terahertz time-domain spectrometer. The measured spectral reflectance is less than 0.3% ranging from 0.2 THz to 0.5 THz and less than 0.1% ranging from 0.5 THz to 2.0 THz. We assembled a terahertz radiometer with this coating as absorber, and discussed its heat transfer in comparison with that of a carbon nanotube array radiometer. This coating is highly absorptive both in terahertz region and in visible light; therefore, the responsivity of this radiometer is easily traceable to National Laser Power Standards. This coating is easily fabricated. It is useful in traceability of terahertz sources and detectors to the SI units.