Laser ablation of SiOx thin films for direct mask writing
The present study of silica thin films illustrates a new way of direct writing diffractive phase elements by means of UVlaser ablation. The concept consists in the conversion of highly absorbing silica layers, which are suitable for laser ablation, into UV transparent structures by thermal annealing, after a direct laser patterning process. This concept has been investigated in detail for several process parameters. As example, a pixel pattern, generated by an appropriate optical design algorithm, is transferred into a phase delay pattern in form of a silica surface relief, which results in a diffractive shaping of a beam transmitted (or reflected) by this structured layer. The direct mask patterning could be achieved at a moderate laser fluence of 350 mJ/cm2 with a 248 nm excimer laser.