Results of applying a non-evaporative mitigation technique to laser-initiated surface damage on fused-silica Page: 4 of 8
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Non-evaporative approach
Mitigation Setup: Slow Melting
Focal spot> Damage area
C02 laser E
Exposure time > Thermal diffusion time
400pm
Damage Site Mitigatetd SiteEvaporative approach
Mitigation Setup: Rapid Evaporation
Damage area >> Focal spot
C02 1aser \ m
TE
Thermal diffusion time >> E xposure time
1.5mm
Damage Site Mitigated SiteFigure 1: Illustrative comparison between evaporative and non-evaporative CO2 laser-based mitigation techniques. Note
the melted appearance of mitigated site in the non-evaporative case as compared to the complete removal of the site in
the evaporative case.
2. RESULTS AND DISCUSSION
2.1 CO2 Laser Mitigation Setup
A simple setup utilizing a CO2 laser was used to perform the mitigation. A schematic of the mitigation setup is shown in
Figure 2. The laser utilized is a quasi-CW Synrad Firestar v20 operating at a wavelength of 10.6 pm. The beam was
allowed to free propagate to a ZnSe aspherical lens where it was weakly focused through the sample plane. The spatial
profile of the beam at the sample plane was Gaussian. A computer system interfaced with the CO2 laser controlled the
exposure parameters during the mitigation.ZnSe mirr
10.6 pm
CO2 Laser ZnSe mirror
PCZnSe wedge Gaussian
beam
ZnSe aspherical lens
or
Fused-silica
sampleBeam
profiler/Power
meterFigure 2: Schematic of the CO2 laser mitigation setup.
Growing surface damage sites were prepared on the output surface of an uncoated 50.8 mm diameter, 10 mm thick
Corning 7980 fused-silica round. The sample was etched and cleaned prior to initiation. A 58 site pattern was initiated
on the output surface of the sample using single pulses from a Nd:YAG laser operating at 355 nm, 7 ns with a 1/e2 beam
diameter of -500 um. This created sites with an average site diameter of Dag = 70 pm and a maximum site diameter of
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Adams, J. J.; Bolourchi, M.; Bude, J. D.; Guss, G. M.; Matthews, M. J. & Nostrand, M. C. Results of applying a non-evaporative mitigation technique to laser-initiated surface damage on fused-silica, article, October 26, 2010; Livermore, California. (https://digital.library.unt.edu/ark:/67531/metadc841324/m1/4/: accessed April 23, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.