Optimization of a laser mitigation process in damaged fused silica

Palmier, Stéphanie; Gallais, Laurent; Commandré, Mireille; Cormont, Philippe; Courchinoux, Roger; Lamaignère, Laurent; Rullier, Jean-Luc; Legros, Philippe

doi:10.1016/j.apsusc.2008.07.178

Cited by 57 publications

(42 citation statements)

References 18 publications

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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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“…Recently, localized CO 2 laser heating of silica glass has been successfully applied to control and mitigate surface damage on optics used in high power laser applications such as inertial confinement fusion (ICF) [3][4][5]. In particular, minimizing damage initiation and shot-to-shot damage growth on UV-grade optics surfaces which have been mechanically polished [6], laser machined [7] or optically damaged [8] is crucial to enhancing overall laser performance.…”

Section: Introductionmentioning

confidence: 99%

Laser smoothing of sub-micron grooves in hydroxyl-rich fused silica

Shen

Matthews

Fair

et al. 2010

Applied Surface Science

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Nano-to micrometer-sized surface defects on UV-grade fused silica surfaces are known to be effectively smoothed through the use of high-temperature localized CO 2 laser heating, thereby enhancing optical properties. However, the details of the mass transport and the effect of hydroxyl content on the laser smoothing of defective silica at submicron length scales is still not completely understood. In this study, we examine the morphological evolution of sub-micron, dry-etched periodic surface structures on type II and type III SiO 2 substrates under 10.6µm CO 2 laser irradiation using atomic force microscopy (AFM). In-situ thermal imaging was used to map the transient temperature field across the heated region, allowing assessment of the Tdependent mass transport mechanisms under different laser-heating conditions. Computational fluid dynamics simulations correlated well with experimental results, and showed that for large effective capillary numbers (N c >2), surface diffusion is negligible and smoothing is dictated by capillary action, despite the relatively small spatial scales studied here. Extracted viscosity values over 1700-2000K were higher than the predicted bulk values, but were consistent with the surface depletion of OH groups, which was confirmed using confocal Raman microscopy.

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“…In the literature, there are reports on glass processing by controlling the glass viscosity below the ablation threshold using a CO 2 laser beam. These works provide an improvement of the surface damage resistance in fused silica optics [14,15], localized repairing of damages in fused silica optics [16][17][18], laser polishing of conventional glasses [19,20] and optical fiber end surfaces [9,21] and, also, in the manufacturing of micro-optical components. In our approach, modulation of CO 2 laser takes an important place for smoothing the silica glass and fiber surfaces without deforming the delicate conical shaped optical fiber deflectors.…”

Section: Co 2 Laser-silica Interactionmentioning

confidence: 99%

CO2 laser polishing of conical shaped optical fiber deflectors

2017

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have been proposed and several types are currently used for tissue ablation. The types of deflector shapes are bare, sidefiring and radial. Bare fiber optic deflectors (basic deflector geometry) transmit the laser energy in the same direction along the fiber. Side-firing optical fiber optical deflectors transmit laser light perpendicular to the fiber axis through specific direction and they are widely used in many medical applications, especially in the prostate tumor ablation [1]. One of the most popular deflector types is radial design. Radial fiber optic deflectors with conically shaped optical fiber end transmit the laser energy radially and the laser energy is homogeneously distributed into a ring-shaped beam. These deflectors are especially used in endovenous laser ablation (EVLA) [2]. Unlike other cone-shaped fiber optical probes [3][4][5][6][7] used for various applications, EVLA operation needs μm-scale, multimode (MM) optical fibers and specific cone-angle values to fulfill the EVLA operation requirements. Thus, multi-mode, larger NA and μm-scale optical fibers are preferred in the operations. The homogeneous, ring-shaped laser energy distribution can be achieved with large cone angles which are detailed in this study. It allows a perfect irradiation of vein walls and their ablation. Among existent fiber processing methods such as chemical, FIB [3][4][5], mechanical polishing method is the best candidate to obtain such desired cone-angles. Furthermore, mechanical polishing process is applicable for mass-production of conical shaped optical fibers used in EVLA operation. In the mechanical polishing process, the deflector geometry is first formed with rough lapping film, then, the surface roughness of the deflector is gradually smoothed by polishing with smoother lapping films [8]. This process is composed of several steps to obtain high quality surface structures and a well-prepared fiber deflector surface eliminates the optical losses such as scattering and back reflection. However, the mechanical fining Abstract A novel method for polishing conical shaped optical fiber deflectors by modulated CO 2 laser exposure is reported. The conical shaped fiber deflector geometry was first formed with rough mechanical polishing, then it was exposed to modulated CO 2 laser operating with wavelength at 10.6 µm to achieve fine polish surfaces. The motivation of this work is to demonstrate that the modulated CO 2 laser exposure approach allows a fiber surface roughness at a nanometer scale without modifying the conical shape of the fiber deflector. The average surface roughness of mechanically polished fiber deflectors with 30 and 9 µm lapping films was smoothed down to 20.4 and 4.07 nm, respectively, after CO 2 laser polishing process. By combining mechanical and laser polishing techniques, fabrication of conical shaped optical fiber deflectors takes less time and it becomes laborer independent and easy to apply.

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Optimization of a laser mitigation process in damaged fused silica

Cited by 57 publications

References 18 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

Laser smoothing of sub-micron grooves in hydroxyl-rich fused silica

CO2 laser polishing of conical shaped optical fiber deflectors

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