Diffusers in silicon-photodiode radiometers

The problems encountered when making radiometric measurements with silicon-photodiode radiometers not incorporating diffusers are discussed, with special attention given to the case where laser beams are involved. A diffuserless radiometer head design is presented which eliminates most of these problems. These problems can also be avoided by using a diffuser. A radiometer head incorporating a diffuser is described, and its properties are studied for three types of diffuser: flashed opal, type-2250 translucent Plexiglas, and a three-piece ground and etched quartz. Graphical data are given for the spatial uniformity, angular response variation, and spectral attenuation associated with radiometer heads incorporating these three types of diffuser. It is shown that, for a wide range of radiometric and photometric applications, the quartz diffuser is the most desirable, although its use results in a somewhat limited angular field of view.