Reflectance Measurements of 3.5-THz Black Coatings Using Terahertz Quantum Cascade Laser Self-Mixing Interferometry

Blackbody on-board calibration targets are key components of spaceborne terahertz radiometers. These must have an emissivity close to 1, uniform temperature, and very low reflectivity. The latter property can be achieved by applying a THz absorbing coating to a surface with a complex reflection geometry. However, the properties of microwave-absorbing media are poorly characterized in the 0.5–5.0 THz. Here, we use a long-path 3.5-THz quantum-cascade laser self-mixing interferometry technique to measure the reflectance of a range of black coatings. Surrey Nanosystems Vantablack S-VIS and N-Science Deep Space Black coatings provide the highest return losses with 28.5 dB and 27.6 dB respectively.