HF-based etching processes for improving laser damage resistance of fused silica optical surfaces [electronic resource].

Published:: Washington, D.C. : United States. Dept. of Energy, 2010.
Oak Ridge, Tenn. : Distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy.
Physical Description:: PDF-file: 32 pages; size: 2.6 Mbytes
Additional Creators:: Lawrence Berkeley National Laboratory, United States. Department of Energy, and United States. Department of Energy. Office of Scientific and Technical Information

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Summary:

The effect of various HF-based etching processes on the laser damage resistance of scratched fused silica surfaces has been investigated. Conventionally polished and subsequently scratched fused silica plates were treated by submerging in various HF-based etchants (HF or NH₄F:HF at various ratios and concentrations) under different process conditions (e.g., agitation frequencies, etch times, rinse conditions, and environmental cleanliness). Subsequently, the laser damage resistance (at 351 or 355 nm) of the treated surface was measured. The laser damage resistance was found to be strongly process dependent and scaled inversely with scratch width. The etching process was optimized to remove or prevent the presence of identified precursors (chemical impurities, fracture surfaces, and silica-based redeposit) known to lead to laser damage initiation. The redeposit precursor was reduced (and hence the damage threshold was increased) by: (1) increasing the SiF₆²⁻ solubility through reduction in the NH4F concentration and impurity cation impurities, and (2) improving the mass transport of reaction product (SiF₆²⁻) (using high frequency ultrasonic agitation and excessive spray rinsing) away from the etched surface. A 2D finite element crack-etching and rinsing mass transport model (incorporating diffusion and advection) was used to predict reaction product concentration. The predictions are consistent with the experimentally observed process trends. The laser damage thresholds also increased with etched amount (up to ≈30 {micro}m), which has been attributed to: (1) etching through lateral cracks where there is poor acid penetration, and (2) increasing the crack opening resulting in increased mass transport rates. With the optimized etch process, laser damage resistance increased dramatically; the average threshold fluence for damage initiation for 30 {micro}m wide scratches increased from 7 to 41 J/cm², and the statistical probability of damage initiation at 12 J/cm² of an ensemble of scratches decreased from ≈100 mm⁻¹ of scratch length to ≈0.001 mm⁻¹.

Report Numbers:

E 1.99:llnl-jrnl-425118
llnl-jrnl-425118

Subject(s):

Engineering

Other Subject(s):

Note:

Published through SciTech Connect.
02/23/2010.
"llnl-jrnl-425118"
Journal of the American Ceramic Society, vol. 94, no. 2, February 1, 2011, pp. 416-428 94 2 ISSN 0002-7820; JACTAW FT
Suratwala, T I; Miller, P E; Bude, J D; Steele, R A; Shen, N; Monticelli, M V; Feit, M D; Laurence, T A; Norton, M A; Carr, C W; Wong, L L.

Funding Information:

W-7405-ENG-48

View MARC record | catkey: 14103898