Fig. 3
From: Surface structuring of glass with submicrometer features using selective laser etching
a Scheme of the determination of the focal dimension. The three positions depict the z-location of the laser focus in comparison to the glass surface and the corresponding modified area. a-1 The modification of the material starts already when the position of the beam focus is located above the surface level. a-2 If the beam focus is on the surface level the applied energy leads to the largest modification width and decreases again if the focus is located below the surface (a-3). b SEM image of a single etched box with a total length of 1 mm depicting the effects of acceleration and deceleration being visible through the different patterning at the left and right end (in the red boxes) of the structure compared to the center (in the green box), where the stage speed is at a sufficient level to achieve a good surface roughness. Outside of this region, the roughness values are increasing to a few hundred nanometers, which will lead to high scattering losses. To avoid these effects and realize more homogeneous surfaces, the box length was increased to 5 mm for further experiments. The writing direction of the laser was along the long axis of the box which results in a smoother surface compared to a structuring along the short axis of the box. c Enlarged image of the central area of the box visualizing the influence of the writing speed on the surface roughness.
