Reflectance Measurements On An Improved Optical Black For Stray Light Rejection From 0.3 To 500 µm

Abstract

The Martin Black process has been used to coat baffles on a wide variety of visible and ultraviolet range instruments. Its infrared applications include baffles for the Infrared Astronomy Satellite and the Spacelab 2 Infrared Telescope. Because of the increased emphasis on stray light suppression in the infrared, the Martin Black process was modified with the objective of creating a better black surface for use in the near-, mid-, and far-infrared regions. These modifications resulted in the creation of an infrared absorbing surface, called Infrablack, which retains the excellent visible absorption properties of its predecessor and has increased infrared absorption. Hemispherical and specular reflectivity and bidirectional reflectance distribution function (BRDF) measurements were made on the Infra-black surface. The specular reflectance at 17° incidence ranges from less than 1% at 60 i.im to less than 15% at 450 /um. BRDF measurements made at the University of Arizona at 10.6 pm, at incidence angles of 10°, 30°, and 60°, indicate that the surface behaves in a nearly Lambertian manner at this wavelength. At 10 incidence the BRDF for Infrablack is about one-seventh that of Martin Black, and the curve is noticeably flatter.