Thermal annealing of laser damage precursors on fused silica surfaces

Journal Article · Mon Mar 19 04:00:00 EDT 2012 · Optics Express

DOI:https://doi.org/10.1117/1.OE.51.12.121817· OSTI ID:1047782

Shen, N; Miller, P E; Bude, J D; Laurence, T A; Suratwala, T I; Steele, W A; Feit, M D; Wang, L L

Previous studies have identified two significant precursors of laser damage on fused silica surfaces at fluenes below {approx} 35 J/cm{sup 2}, photoactive impurities in the polishing layer and surface fractures. In the present work, isothermal heating is studied as a means of remediating the highly absorptive, defect structure associated with surface fractures. A series of Vickers indentations were applied to silica surfaces at loads between 0.5N and 10N creating fracture networks between {approx} 10{micro}m and {approx} 50{micro}m in diameter. The indentations were characterized prior to and following thermal annealing under various times and temperature conditions using confocal time-resolved photo-luminescence (CTP) imaging, and R/1 optical damage testing with 3ns, 355nm laser pulses. Significant improvements in the damage thresholds, together with corresponding reductions in CTP intensity, were observed at temperatures well below the glass transition temperature (T{sub g}). For example, the damage threshold on 05.N indentations which typically initiates at fluences <8 J/cm{sup 2} could be improved >35 J/cm{sup 2} through the use of a {approx} 750 C thermal treatment. Larger fracture networks required longer or higher temperature treatment to achieve similar results. At an annealing temperature > 1100 C, optical microscopy indicates morphological changes in some of the fracture structure of indentations, although remnants of the original fracture and significant deformation was still observed after thermal annealing. This study demonstrates the potential of using isothermal annealing as a means of improving the laser damage resistance of fused silica optical components. Similarly, it provides a means of further understanding the physics associated with optical damage and related mitigation processes.

• Research Organization: Lawrence Livermore National Laboratory (LLNL), Livermore, CA
• Sponsoring Organization: USDOE
• DOE Contract Number: W-7405-ENG-48
• OSTI ID: 1047782
• Report Number(s): LLNL-JRNL-539671
• Journal Information: Optics Express, Journal Name: Optics Express Journal Issue: 10 Vol. 20
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ANNEALING
DEFECTS
DEFORMATION
FRACTURES
GLASS
HEATING
IMPURITIES
LASERS
MITIGATION
MORPHOLOGICAL CHANGES
OPTICAL MICROSCOPY
PHYSICS
POLISHING
SILICA
TESTING
TRANSITION TEMPERATURE