skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

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

Abstract

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{sub 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{sub 2} substrates under 10.6 {micro}m CO{sub 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 T-dependent 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{sub 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.

Authors:
; ; ; ; ; ; ;
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
974861
Report Number(s):
LLNL-JRNL-420282
Journal ID: ISSN 0169-4332; ASUSEE; TRN: US201007%%860
DOE Contract Number:  
W-7405-ENG-48
Resource Type:
Journal Article
Journal Name:
Applied Surface Science
Additional Journal Information:
Journal Volume: 256; Journal Issue: 12; Journal ID: ISSN 0169-4332
Country of Publication:
United States
Language:
English
Subject:
42 ENGINEERING; ATOMIC FORCE MICROSCOPY; COMPUTERIZED SIMULATION; DEFECTS; DIFFUSION; FLUID MECHANICS; HEATING; IRRADIATION; LASERS; MICROSCOPY; OPTICAL PROPERTIES; SILICA; SUBSTRATES; TRANSIENTS; TRANSPORT; VISCOSITY

Citation Formats

Shen, N, Matthews, M J, Fair, J E, Britten, J A, Nguyen, H T, Cooke, D, Elhadj, S, and Yang, S T. Laser smoothing of sub-micron grooves in hydroxyl-rich fused silica. United States: N. p., 2009. Web.
Shen, N, Matthews, M J, Fair, J E, Britten, J A, Nguyen, H T, Cooke, D, Elhadj, S, & Yang, S T. Laser smoothing of sub-micron grooves in hydroxyl-rich fused silica. United States.
Shen, N, Matthews, M J, Fair, J E, Britten, J A, Nguyen, H T, Cooke, D, Elhadj, S, and Yang, S T. 2009. "Laser smoothing of sub-micron grooves in hydroxyl-rich fused silica". United States. https://www.osti.gov/servlets/purl/974861.
@article{osti_974861,
title = {Laser smoothing of sub-micron grooves in hydroxyl-rich fused silica},
author = {Shen, N and Matthews, M J and Fair, J E and Britten, J A and Nguyen, H T and Cooke, D and Elhadj, S and Yang, S T},
abstractNote = {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{sub 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{sub 2} substrates under 10.6 {micro}m CO{sub 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 T-dependent 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{sub 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.},
doi = {},
url = {https://www.osti.gov/biblio/974861}, journal = {Applied Surface Science},
issn = {0169-4332},
number = 12,
volume = 256,
place = {United States},
year = {Fri Oct 30 00:00:00 EDT 2009},
month = {Fri Oct 30 00:00:00 EDT 2009}
}