Black coatings BSDF database

Straylight requirements for optical instruments become ever more stringent. This applies not only to optical instruments in space, but also extends to optical ground support equipment (OGSE) and any other instrument that is sensitive to straylight. One of the means to control the straylight within instruments and OGSE’s is the application of black coatings, e.g. on optical mounts, lens barrels and baffles. There are different types of black coatings on the market. The choice of a suitable black coating does not only depend on its optical properties, but also on the compatibility with the substrate material and its geometry. For many coatings, the manufacturers provide only a hemispherical reflectivity value, which is not very suitable for straylight predictions, as it does not include the angle dependent scattering behavior. This information is provided by the Bi-directional Scatter Distribution Function (BSDF). The optics and opto-electronics laboratories (OOEL) at ESTEC receive many requests to characterize black coatings by measuring the BSDF. The OOEL has created a database for black coatings to collect the BSDF data in support to space industry to facilitate the selection of the most suitable black coating and make more accurate predictions of straylight at instrument level. The database, called ‘Black Coatings BSDF Database’, will be presented here to showcase its functionalities. We will present some examples of BSDF data to demonstrate the added value over hemispherical reflectivity. The BSDF data contained within the Black Coatings BSDF Database is structured according to coating type, measured wavelength and, if that information was available, according to specific information on the coating and/or substrate. So far, all BSDF measurements data has been measured at the OOEL using the two currently available CASI and Albatross TT scatterometers. Additional data will be added in the future. The European space industry is invited to contribute to the Black Coatings BSDF Database by either providing a sample to be characterized or contribute with already measured BSDF data. The Black Coatings BSDF database will be a database created for and by the European space industry. Access to the database is free and can be requested by contacting the OOEL via: ooel@esa.int.