High-reflectance diffuse coating

The second method, which is particularly useful with extended sources such as diffusing optical fibers, is to place the diffuser into a sphere that has a highly reflective inside coating. This randomizes the light by multiple reflections and a known small fraction escapes through an output port to be detected, again usually by... 

Integrating sphere n. A sphere coated inside with a highly reflective, diffuse material and used for the measurement of luminous flux. If the internal surface is perfectly diffuse, the intensity of any part of the sphere is the same. Many instruments used for reflectance measurements utilize such a device for measuring the diffuse or total reflectance from a sample material relative to a reference material. 

The schematic setup of a diffuse reflectance spectrometer which is obtained by supplying a normal UV-VIS spectrometer with a diffuse reflectance accessory is shown in Fig. 18. The core is an integrating sphere coated with a highly reflective material that collects the scattered radiation and leads it to the detector. The light remitted by the sample is compared with that of a white standard as the reference. Zeolite layers of ca. 5 mm depth are generally sufficient to meet the condition of infinite thickness. A typical sample cell furnished with an evacuated Infrasil double window and designed for temperature control and evacuation is depicted in the lower part of Fig. 18 [32]. Other cell constructions have been reported by Klier [31] and Schoonheydt [34]. 

Finally, the reflection of light from the copper coating obtained from a pure sulfate solution is mostly diffuse reflection. The structural characteristics of this copper surfaces which enabled a high degree of diffuse reflection with a negligible degree of mirror reflection are that the lateral parts of the surface were larger than the flat parts. 

---