F2-laser ablation patterning of dielectric layers
Spatially defined patterning of multi-layer dielectric optical systems by laser-induced ablation is demonstrated. A 49-layer high-reflectivity mirror for 193-nm light was irradiated with F2-laser light through the CaF2-substrate to cleanly remove the whole dielectric stack by rear-sided ablation. The 157-nm light is absorbed efficiently by dielectric layers such as SiO2 and Al2O3 that are typically used for ultraviolet (UV) transmission at 193-nm and longer wavelengths. Thus it is possible to ablate highly reflective UV-laser mirrors (HR 193 nm) and to create dielectric masks that withstand high power levels at 193 nm. A single 157-nm pulse with a fluence of less than 500 mJ/cm2 is sufficient to cleanly ablate the whole layer stack with sharp edges and without debris deposition.
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