Design and experimental research of angle self-compensation setup for BSDF measurement

When using a single reference to measure the bi-directional scattering distribution function (BSDF), the incident zenith angle of the tested sample must be identical to that of the reference. In order to get the hemisphere space scattering characteristic on the sample surface, usually a motor drives the sample tilting, then the incident zenith angle is changed and needs to be the compensated by another motor. We mathematically deduce the expression of compensation angle when the incident zenith angle is changed by the rotation of motor. After the incident angle is compensated, the scattering zenith angle and azimuth angle are deduced too. The uncertainty of the system is 0.75%. Scattering measurements are performed on copper sample with visible light under different temperatures.