Measurement method of optical scatter using a STAR GEM as a scatterometer

A STAR GEM as a scatterometer can measure diffuse reflection spectra. The acronym of STAR GEM is from the capital letters of Scatter, Transmission, and Absolute Reflection measurements using a Geminated Ellipsoid Mirror. A biconical accessory, such as the STAR GEM, has the advantage that it has very high collection efficiency and the ability to measure scattered reflected light from very small samples. However, it is generally thought of as a qualitative device. It becomes clear that the STAR GEM is superior to a goniometer on the study to measure absolute reflectance of a specular sample. Only the goniometer and its family can quantitatively measure the bidirectional reflectance distribution function (BRDF) of a sample. The purpose of this paper is to describe the possibilities and problems for the STAR GEM to measure the BRDF of a sample.