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UV transparent phase masks are used in various laser applications like fabrication of Bragg gratings in optical fibers or micro patterning by high power laser ablation. Normally they are fabricated by a costly lithographic process including e-beam writing and reactive ion etching. We propose a new fabrication method based on UV laser ablation. The process consists of three steps. First, a silicon suboxide coating (SiOx with x < 2) with a predefined thickness is deposited on a fused silica substrate. Second, due to its strong UV-absorption, this coating can be removed in defined areas by excimer laser ablation at 193 nm or 248 nm leading to the desired phase pattern in form of a binary depth profile. Third, by applying a thermal annealing process, the remaining SiOxcoating is oxidized to UV-transparent SiO2, resulting in a UV-grade surface relief element. The precisely defined interface between substrate and layer allows for ablation with exact depth control and perfect optical surface quality. Such SiO2 phase masks feature a large processed area, high efficiency for VUV to NIR radiation and can be customized e.g. for perfect zero order suppression. Applications of such phase gratings for materials processing with a UV-femtosecond laser are demonstrated. Using the phase gratings in a mask projection configuration, submicron patterns are created in a variety of materials.

Fabrication of SiO2 Phase Gratings by UV Laser Patterning of Silicon Suboxide Layers and Subsequent Oxidation