Laser scattering on aluminum surfaces with random and periodic height distributions

With the aim to investigate the effect of surface roughness on laser scattering, a Total Integrated Scattering (TIS) measurement device was established. The scattering properties of a 1319 nm Nd:YAG laser under different surface roughnesses and the applicability of the Beckmann theory were discussed. First, the high purity aluminum samples with random and periodic roughness distributions were obtained by using diamond turning and their three-dimensional topographies and root-mean-square roughnesses were measured by an interference microscopy. Then, the TIS measurement device was established based on integrating spheres to measure the TIS values of every samples. Finally, the experimental TIS value was compared with the calculated one from the Beckmann theory. The comparison indicates that experimental results show acceptable agreement with Beckmann theory when the roughness is smaller than 20 nm. However, it has a larger difference when the roughness is bigger than 20 nm. It points out that the surface roughness of the samples affect the space distribution of the scattering intensity and the bigger the roughness is, the smaller the ratio of specular intensity to the total scattering intensity could be. The Beckmann theory is quite fit for the rough surface with random height distribution.