Abstract
Scratches are deleterious to precision optics because they can obscure and modulate incident laser light, which will increase the probability of damage to optical components. We here imitated the generation of brittle and ductile scratches during polishing process and endeavored to find out the possible influence of scratches on laser induced damage. Brittle scratches can be induced by spiking large sized abrasives and small abrasives may only generate ductile scratches. Both surface roughness and transmittivity are degraded due to the appearance of brittle scratches while ductile scratches make little difference to surface roughness and transmittance. However, ductile and brittle scratches greatly increase the density of damage about one order of magnitude relative to unscratched surface. In particular, ductile scratches also play an unignorable role in laser induced damage, which is different from previous knowledge. Furthermore, ZrO2 and Al2O3 polished surfaces appear to perform best in terms of damage density.
Highlights
Our results indicate that ductile scratches can be damage precursors and can trigger damage to fused silica, which is different from previous results that ductile deformation may not be harmful to optical components in high power laser systems[18,19]
The artificial scratches were investigated to find out their possible effects on surface quality and laser damage
The results show that CeO2 is more efficient than Al2O3 and ZrO2 in polishing fused silica and CeO2, Al2O3 and ZrO2 are all capable of polishing out a smooth surface
Summary
The Gaussian laser pulse (8 ns@355 nm, beam waist 800 μm) was focused onto the rear surface of samples and the repetition rate was 10 Hz. The damage test protocol adopted was raster scan. ZrO2-polished sample is superior to other samples; (b) surface of sample D before raster scan damage testing; (c) sample D after damage testing, from which it is clean that both brittle and ductile scratches can cause laserinduced damage. It is the chemical reactions that accelerate the material removal rate during the polishing of glass, 1 μm/h for CeO2 abrasive versus 0.33 μm/h for ZrO2.
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