Integrating Spheres for Measurements Between 0185 μm and 12 μm

Abstract

A new system for absolute total diffuse transmission and reflection measurements using two integrating spheres is described; it extends the normal spectral range into the uv and ir. Furthermore, as part of the system, a unique self-calibrating technique has been incorporated. One sphere is coated with BaSO4 for use between wavelengths of 0.185 µm and 2.0 µm, and the other is coated with sulfur flowers for use between 1.5 µm and 12 µm. The BaSO4 and sulfur fulfill the diffuseness and high reflectance characteristics necessary for an integrating sphere. The feature of the system for calibration of the spheres uses goniophotometric measurements of diffuse transmission and reflection. These reflection intercalibrations are better in the visual range than a fraction of a percent (absolutely); however, transmission intercalibrations on quasi-specular samples may have absolute differences of several percent, thus requiring a goniophotometric transmission measurement as the valid determination.