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Title: Utilization of Magnetorheological Finishing as a Diagnostic Tool for Investigating the Three-Dimensional Structure of Fractures in Fused Silica

Abstract

We have developed an experimental technique that combines magnetorheological finishing (MRF) and microscopy to examine fractures and/or artifacts in optical materials. The technique can be readily used to provide access to, and interrogation of, a selected segment of a fracture or object that extends beneath the surface. Depth slicing, or cross-sectioning at selected intervals, further allows the observation and measurement of the three-dimensional nature of the sites and the generation of volumetric representations that can be used to quantify shape and depth, and to understand how they were created, how they interact with surrounding material, and how they may be eliminated or mitigated.

Authors:
; ; ; ; ;
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
928166
Report Number(s):
UCRL-PROC-217132
TRN: US200815%%761
DOE Contract Number:
W-7405-ENG-48
Resource Type:
Conference
Resource Relation:
Conference: Presented at: Boulder Damage Symposium XXXII, Boulder, CO, United States, Sep 19 - Sep 21, 2005
Country of Publication:
United States
Language:
English
Subject:
42 ENGINEERING; 71 CLASSICAL AND QUANTUMM MECHANICS, GENERAL PHYSICS; FRACTURES; MICROSCOPY; SHAPE; SILICA

Citation Formats

Menapace, J A, Davis, P J, Steele, W A, Wong, L L, Suratwala, T I, and Miller, P E. Utilization of Magnetorheological Finishing as a Diagnostic Tool for Investigating the Three-Dimensional Structure of Fractures in Fused Silica. United States: N. p., 2005. Web.
Menapace, J A, Davis, P J, Steele, W A, Wong, L L, Suratwala, T I, & Miller, P E. Utilization of Magnetorheological Finishing as a Diagnostic Tool for Investigating the Three-Dimensional Structure of Fractures in Fused Silica. United States.
Menapace, J A, Davis, P J, Steele, W A, Wong, L L, Suratwala, T I, and Miller, P E. Fri . "Utilization of Magnetorheological Finishing as a Diagnostic Tool for Investigating the Three-Dimensional Structure of Fractures in Fused Silica". United States. doi:. https://www.osti.gov/servlets/purl/928166.
@article{osti_928166,
title = {Utilization of Magnetorheological Finishing as a Diagnostic Tool for Investigating the Three-Dimensional Structure of Fractures in Fused Silica},
author = {Menapace, J A and Davis, P J and Steele, W A and Wong, L L and Suratwala, T I and Miller, P E},
abstractNote = {We have developed an experimental technique that combines magnetorheological finishing (MRF) and microscopy to examine fractures and/or artifacts in optical materials. The technique can be readily used to provide access to, and interrogation of, a selected segment of a fracture or object that extends beneath the surface. Depth slicing, or cross-sectioning at selected intervals, further allows the observation and measurement of the three-dimensional nature of the sites and the generation of volumetric representations that can be used to quantify shape and depth, and to understand how they were created, how they interact with surrounding material, and how they may be eliminated or mitigated.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Fri Nov 11 00:00:00 EST 2005},
month = {Fri Nov 11 00:00:00 EST 2005}
}

Conference:
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  • The laser-induced damage threshold of fused-silica samples processed via magnetorheological finishing is investigated for polishing compounds depending on the type of abrasive material and the post-polishing surface roughness. The effectiveness of laser conditioning is examined using a ramped pre-exposure with the same 351-nm, 3-ns Gaussian pulses. Lastly, we examine chemical etching of the surface and correlate the resulting damage threshold to the etching protocol. A combination of etching and laser conditioning is found to improve the damage threshold by a factor of ~3, while maintaining <1-nm surface roughness.
  • Over the past four years we have advanced Magnetorheological Finishing (MRF) techniques and tools to imprint complex continuously varying topographical structures onto large-aperture (430 x 430 mm) optical surfaces. These optics, known as continuous phase plates (CPPs), are important for high-power laser applications requiring precise manipulation and control of beam-shape, energy distribution, and wavefront profile. MRF's unique deterministic-sub-aperture polishing characteristics make it possible to imprint complex topographical information onto optical surfaces at spatial scale-lengths approaching 1 mm and surface peak-to-valleys as high as 22 {micro}m. During this discussion, we will present the evolution of the MRF imprinting technology and themore » MRF tools designed to manufacture large-aperture 430 x 430 mm CPPs. Our results will show how the MRF removal function impacts and limits imprint fidelity and what must be done to arrive at a high-quality surface. We also present several examples of this imprinting technology for fabrication of phase correction plates and CPPs for use in high-power laser applications.« less
  • Magnetorheological finishing (MRF) techniques have been developed to manufacture continuous phase plates (CPP's) and custom phase corrective structures on polished fused silica surfaces. These phase structures are important for laser applications requiring precise manipulation and control of beam-shape, energy distribution, and wavefront profile. The MRF's unique deterministic-sub-aperture polishing characteristics make it possible to imprint complex topographical information onto optical surfaces at spatial scale-lengths approaching 1 mm. In this study, we present the results of experiments and model calculations that explore imprinting two-dimensional sinusoidal structures. Results show how the MRF removal function impacts and limits imprint fidelity and what must bemore » done to arrive at a high quality surface. We also present several examples of this imprinting technology for fabrication of phase correction plates and CPPs for use at high fluences.« less
  • Laser induced damage initiation on fused silica optics can limit the lifetime of the components when used in high power UV laser environments. Foe example in inertial confinement fusion research applications, the optics can be exposed to temporal laser pulses of about 3-nsec with average fluences of 8 J/cm{sup 2} and peak fluences between 12 and 15 J/cm{sup 2}. During the past year, we have focused on optimizing the damage performance at a wavelength of 355-nm (3{omega}), 3-nsec pulse length, for optics in this category by examining a variety of finishing technologies with a challenge to improve the laser damagemore » initiation density by at least two orders of magnitude. In this paper, we describe recent advances in improving the 3{omega} damage initiation performance of laboratory-scale zirconium oxide and cerium oxide conventionally finished fused silica optics via application of processes incorporating magnetorheological finishing (MRF), wet chemical etching, and UV laser conditioning. Details of the advanced finishing procedures are described and comparisons are made between the procedures based upon large area 3{omega} damage performance, polishing layer contamination, and optical subsurface damage.« less
  • Antireflection (AR) coatings typically damage at the interface between the substrate and coating. Therefore the substrate finishing technology can have an impact on the laser resistance of the coating. For this study, AR coatings were deposited on Yb:S-FAP [Yb{sup 3+}:Sr{sub 5}(PO{sub 4}){sub 3}F] crystals that received a final polish by both conventional pitch lap finishing as well as magnetorheological finishing (MRF). SEM images of the damage morphology reveals laser damage originates at scratches and at substrate coating interfacial absorbing defects. Previous damage stability tests on multilayer mirror coatings and bare surfaces revealed damage growth can occur at fluences below themore » initiation fluence. The results from this study suggest the opposite trend for AR coatings. Investigation of unstable HR and uncoated surface damage morphologies reveals significant radial cracking that is not apparent with AR damage due to AR delamination from the coated surface with few apparent cracks at the damage boundary. Damage stability tests show that coated Yb:S-FAP crystals can operate at 1057 nm at fluences around 20 J/cm{sup 2} at 10 ns; almost twice the initiation damage threshold.« less