Abstract
Multiple-pulse S-on-1 laser damage experiments were carried out in the bulk of synthetic fused silica at 355 nm and 266 nm. Two beam sizes were used for each wavelength and the pulse duration was 8 ns. The results showed a fatigue effect that is due to cumulative material modifications. The modifications have a long lifetime and the fatigue dynamics are independent of the used beam sizes but differ for the two wavelengths. Based on the fact that, in the context of material-modification induced damage, the damage thresholds for smaller beams are higher than for larger beams, we discuss possible mechanisms of damage initiation.
Highlights
Synthetic fused silica is the best-performing amorphous optical material in terms of laserinduced damage at wavelengths close to 1 μm and a large number of laser damage studies has been published [1]
The modification may possibly influence the propagation of the laser beam, so that the peak fluence inside the sample becomes higher than the peak fluence of the first pulse
Bosyi and Efimov showed that thermal self-focusing or formation of an index gradient ‘lens’ by material compaction may explain their experimental data in different irradiation conditions [8, 9]
Summary
Synthetic fused silica is the best-performing amorphous optical material in terms of laserinduced damage at wavelengths close to 1 μm and a large number of laser damage studies has been published [1]. The first studies of synthetic fused silica in the UV range mostly aimed at low-fluence applications like exposure of photosensitive polymers for microelectronics fabrication These studies, carried out at excimer laser wavelengths, revealed that high OH-content synthetic fused silica from different manufacturers may show significant differences in terms of laser-induced absorption [2, 3]. High UV-fluences can be generated by frequency conversion of solid state lasers emitting close to 1 μm wavelength and important space projects using these lasers are realized [7] generating a need to understand multi-pulse laser damage issues It was observed in various optical materials that multi-pulse irradiation leads to a decrease of the laser-induced damage threshold with increasing number of pulses. One may mention that at these wavelengths no laser-induced absorption could be evidenced in synthetic fused silica, even at very high pulse numbers [16, 17]
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