OPTICAL CONTAMINATION ASSESSMENT BY BIDIRECTIONAL REFLECTANCE-DISTRIBUTION FUNCTION (BRDF) MEASUREMENT

Sorme optical systems can tolerate only a small amount of light scattering from mirror surfaces within the system. If low scatter mirrors are used, they must be monitored by some means to be sure that contamination does not increase the intrinsic scatter. The measurement technique of Bidirectional Reflectance-Distribution Function (BRDF) is presented as a method to monitor the scatter of mirror surfaces. The test apparatus needed to measure BRDF is discussed. Curves are given which show how such contaminants as dust, hydrocarbon oil, acrylic, and peelable coating residue affect BRDF. It is shown that BRDF measurement provides a practical and accurate method of measuring the scatter degradation of a low scatter mirror surface that has become contaminated.