Absorbing coatings and diffuse reflectors for the Herschel platform sub-millimeter spectrometers HIFI and PACS

Absorbing coatings for the HIFI and PACS spectrometers aboard the Herschel platform have been developed and optically characterized. Using radiation from an optically pumped far-infrared laser at wavelengths in the 90-900 /spl mu/m range, the specular as well as the diffuse reflection - described by the bi-directional reflection distribution function - have been determined. The influence of polarization has been addressed too. Moreover, the absorption of non-absorbing diffusely reflecting surfaces, to be used for integrating spheres, has been determined using a calorimetric method.