Scattering effects of glass-embedded microstructures by roughness controlled fs-laser micromachining

We report a full roughness analysis carried out upon the internal walls of fs-fabricated micro-structures embedded in fused silica glass. In addition to the standard mapping methods based on RMS evaluation, we performed a spectral analysis to compare different types of surface morphology. In detail, introducing the correlation length L _c as a key parameter to describe the profile periodicity, we highlight that the bottom- top- and side-wall of a square micro-channel show a different surface order and differently affect the light scattering. This is further validated by fast Fourier transform calculations and supported by beam transmission holograms. Here we suggest that proper beam shaping could ensure uniform energy distribution and low scattering effects. (paper)