Beam diameter dependence of surface damage threshold of fused silica fibers and preforms for nanosecond laser treatment at 1064Â nm wavelength

This paper pays particular attention to the influence of the laser beam diameter on damage resistance. All-silica fiber types (LEONI) with different core diameters (100-600 μm) were investigated using beam diameters in a range from 30 μm to 100 μm. For comparison experiments on fused silica preform material (Heraeus F300) were performed. On one hand, surface LIDT of fused silica preform material decreases significantly with increasing beam size. A model considering a random distribution of point defects explains the experimental data qualitatively. On the other hand, LIDT of fiber end facets stays constant. White light microscopy results suggest that the point defect density on fiber end facets is lower compared to the preform surface due to an excellent surface polish quality.