Surface analysis of femtosecond laser processed materials by using different interferometric modalities

Knowledge about the surface topography is important in terms of precision, resolution, adhesive force, or simply material quality. We measured the surface structure of femtosecond laser processed materials by using digital-interferometric analysis technique. The materials were PMMA, PDMS and fused silica. For surface modification, a femtosecond laser at 1030 nm wavelength with 350 fs pulse duration was used. The laser was focused with 0.6 numerical aperture objective lens onto the surface of the materials. The samples were moved lateral during the cutting process to create different ablation patterns. The imaging technique was used in transmission and reflection mode. Using both modalities gives information about the surface topography and changes in optical density or refractive index of the material. Furthermore, we used scanning electron microscopy to compare the imaging techniques. Using digital interferometry can lead to quantitative values for both refractive index and real height of surface topography. Refractive index changes in the order of E-2 and surface roughness up to several hundred nanometers were measured.