Absolute calibration in FIR radiometric measurements

A truly rigorous and quantitative approach to Black Body radiation is the fundamental starting point of experimental Radiometry in the region of Far Infrared and Millimeter waves (FIR). Absolute (i.e. calibrated) measurements of electromagnetic radiation are widely used in many areas of Physics, from Plasma Diagnostics in Nuclear Fusion, to Radio Astronomy and Atmospheric Physics. Along the years different Authors have used personalized constants and definitions, sometimes arbitrary, and the choices were often hidden into papers and analysis software, hence making impossible to compare properly the results, even within the same field of research. In Boyd's words [1]: