Abstract
Femtosecond laser pulses used in a regime below the ablation threshold have two noticeable effects on Fused Silica (a-SiO2): they locally increase the material refractive index and modify its HF etching selectivity. The nature of the structural changes induced by femtosecond laser pulses in fused silica is not fully understood. In this paper, we report on nanoindentation and birefringence measurements on fused silica exposed to low-energy femtosecond laser pulses. Our findings further back the hypothesis of localized densification effect even at low energy regime.
Highlights
Femtosecond laser pulses interact in unusual ways with matter
In fused silica (α-SiO2) in particular, various interesting effects of femtosecond laser irradiation have been observed at energy levels below the ablation threshold
Davis et al [2] demonstrated that the refractive index of fused silica can be locally increased and Marcinkevičius et al [3] showed that at higher energy levels, an increase in etching selectivity to HF acid is observed
Summary
Femtosecond laser pulses interact in unusual ways with matter. In dielectrics, non-linear effects driven by multi-photon absorption are observed [1]. In fused silica (α-SiO2) in particular, various interesting effects of femtosecond laser irradiation have been observed at energy levels below the ablation threshold. Davis et al [2] demonstrated that the refractive index of fused silica can be locally increased and Marcinkevičius et al [3] showed that at higher energy levels (but yet still below the ablation threshold), an increase in etching selectivity to HF acid is observed. Successful applications have been demonstrated since but the underlying physical mechanism to explain these two effects remains elusive [4, 5, 6]. The present study aims at improving our knowledge of femtosecond laser irradiation effects on fused silica through novel experimental approaches. We used two techniques, nanoindentation and digital holography microscopy to investigate material density changes and related internal stress resulting from the laser exposure
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