Effect of beryllium topography on BRDF measurements

The Bidirectional Reflectance Distribution Function (BRDF) of beryllium is important for a ray-tracing simulation to evaluate the effect of reflected light on optical diagnostics in the fusion device ITER. However, the BRDF for beryllium has not been investigated yet and is currently lacking. To fill this gap, this study measured BRDFs of beryllium specimens with different topographies using goniophotometers and optimized optical reflection models. Additionally, various surface topographic parameters were computed, and their correlation with parameters for the optical reflection models was explored. As a result, it was found that topographic parameters related to slope offer a certain correlation with the parameters of the reflection model. This can be useful for determining the optical reflection properties of materials for which direct BRDF measurements are not possible.