Localized silica re-fusion for laser damage mitigation

Bouchut, Philippe; Delrive, Laurence; Decruppe, Daniel; Garrec, Pierre

doi:10.1117/12.521861

Cited by 8 publications

(6 citation statements)

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“…Vigorous investigation 2 of this approach, however, didn't begin for another 20 years when the need for damage growth mitigation became more evident. Since then LLNL, CEA 3,4 and other laboratories 5 have continued to develop laser based mitigation strategies. It is important to control the morphology of the surfaces resulting from such mitigation because mitigated sites modulate the incoming laser beam and can potentially cause deleterious downstream intensification.…”

Section: Introductionmentioning

confidence: 99%

Densification and residual stress induced by CO 2 laser-based mitigation of SiO 2 surfaces

et al. 2010

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Knowing the ultimate surface morphology resulting from CO 2 laser mitigation of induced laser damage is important both for determining adequate treatment protocols, and for preventing deleterious intensification upon subsequent illumination of downstream optics. Physical effects such as evaporation, viscous flow and densification can strongly affect the final morphology of the treated site. Evaporation is a strong function of temperature and will play a leading role in determining pit shapes when the evaporation rate is large, both because of material loss and redeposition. Viscous motion of the hot molten material during heating and cooling can redistribute material due to surface tension gradients (Marangoni effect) and vapor recoil pressure effects. Less well known, perhaps, is that silica can densify as a result of structural relaxation, to a degree depending on the local thermal history. The specific volume shrinkage due to structural relaxation can be mistaken for material loss due to evaporation. Unlike evaporation, however, local density change can be reversed by post annealing. All of these effects must be taken into account to adequately describe the final morphology and optical properties of single and multiple-pass mitigation protocols. We have investigated, experimentally and theoretically, the significance of such densification on residual stress and under what circumstances it can compete with evaporation in determining the ultimate post treatment surface shape. In general, understanding final surface configurations requires taking all these factors including local structural relaxation densification, and therefore the thermal history, into account. We find that surface depressions due to densification can dominate surface morphology in the non-evaporative regime when peak temperatures are below 2100K.

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Section: Introductionmentioning

confidence: 99%

Densification and residual stress induced by CO 2 laser-based mitigation of SiO 2 surfaces

et al. 2010

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“…[12] The debris is composed of the SiO x (0 < x < 2) species with a nonstoichiometric formula, which could induce a decrease in LIDT by absorbing photons in the visible region and local enhancement of roughness. [6] The optical properties of the nonstoichiometric SiO x species have also been studied in previous work. [16,17] Anyway, the black ring indicates that the surface temperature is above the evaporation point of fused silica (T > T e ).…”

Section: Resultsmentioning

confidence: 99%

“…Although the surface damage initiated at 3ω on NIF silica optics will encompass only a fractional area, studies have shown that the damage can grow rapidly with the number of shots at a laser fluence of 5 J/cm 2 to 6 J/cm 2 , which is just a factor of two below the LIDT of a pristine silica surface. [5,6] Therefore, mitigation of surface damage growth is essential for the lifetime extension of the expensive large-scale laser optics when the surface damage is small.…”

Section: Introductionmentioning

confidence: 99%

Irradiation effects of CO₂laser parameters on surface morphology of fused silica

et al. 2011

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“…Krol et al [5] and Dijon et al [8] utilized a statistical description to analyze the LIDTs of substrate and coating of optics. At present, most studies on mitigated sites focus on how to mitigate the damage sites in an optimal way and decrease the downstream intensification resulting from the mitigated sites [9][10][11]. In these works, the average damage threshold of mitigated sites was used to evaluate the damage behavior of mitigated sites.…”

Section: Introductionmentioning

confidence: 99%

Characterization of 355 nm laser-induced damage of mitigated damage sites in fused silica

Jiang¹,

Xi²,

Yuan³

et al. 2012

Laser Phys.

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The laser-induced damage threshold (LIDT) is one of the important methods to determine the mitigation efficiency of mitigated damage sites in fused silica optics. In this work, two sizes of laser beam with a wavelength of 355 nm and a pulse width of 6.3 ns are used to test the LIDTs and properties of mitigated damage sites. Meanwhile, the R-on-1 average threshold and threshold distribution are used to analyze damage behavior of mitigated sites. It is found that the R-on-1 average threshold shows an S-shaped curve and the threshold distribution obeys a normal law for the mitigated damage sites, which is similar to the law of pristine substrates reported before. The LIDT discrepancy of mitigated sites tested with different sizes of laser beam is attributed to the spot-size effect of the test laser beam, i.e., the LIDT of the mitigated site increases with decreasing test laser spot size. It is shown that most damage occurs at the edge of the laser affected zone, which could be ascribed to the weak location between laser affected and unaffected zones. Finally, the correlations between damage size and the laser fluence which causes damage initiation or damage growth are investigated for the pristine substrate and mitigated sites, and can be fitted by an exponential law.

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Localized silica re-fusion for laser damage mitigation

Cited by 8 publications

References 0 publications

Densification and residual stress induced by CO 2 laser-based mitigation of SiO 2 surfaces

Densification and residual stress induced by CO 2 laser-based mitigation of SiO 2 surfaces

Irradiation effects of CO₂laser parameters on surface morphology of fused silica

Characterization of 355 nm laser-induced damage of mitigated damage sites in fused silica

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Localized silica re-fusion for laser damage mitigation

Cited by 8 publications

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Densification and residual stress induced by CO 2 laser-based mitigation of SiO 2 surfaces

Densification and residual stress induced by CO 2 laser-based mitigation of SiO 2 surfaces

Irradiation effects of CO2laser parameters on surface morphology of fused silica

Characterization of 355 nm laser-induced damage of mitigated damage sites in fused silica

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Irradiation effects of CO₂laser parameters on surface morphology of fused silica