&lt;title&gt;The National Ignition Facility: the world's largest optics and laser system&lt;/title&gt;

Moses, E. I.; Campbell, J. H.; Stolz, Christopher J.; Wüest, C.

doi:10.1117/12.500351

Cited by 63 publications

(36 citation statements)

References 37 publications

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“…In some use applications, the removal or minimization of SSD is required for improving the material strength (e.g. spacecraft, underwater windows/barriers, and other military applications) where the surface flaws determine the ultimate strength or for reducing/eliminating laser-induced damage (e.g., high-peak-power laser applications [2]). For laser optic applications, SSD is believed to serve as a reservoir for absorbing precursors that will heat up and explode upon irradiation with high fluence laser light [3].…”

Section: Introductionmentioning

confidence: 99%

Sub-surface mechanical damage distributions during grinding of fused silica

Suratwala

Wong

Miller

et al. 2006

Journal of Non-Crystalline Solids

252

169

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The distribution and characteristics of surface cracking (i.e. sub-surface damage or SSD) formed during standard grinding processes has been investigated on fused silica glass. The SSD distributions of the ground surfaces were determined by: 1) creating a shallow (18-108 μm) wedge/taper on the surface by magneto-rheological finishing; 2) exposing the SSD by HF acid etching; and 3) performing image analysis of the observed cracks from optical micrographs taken along the surface taper. The observed surface cracks are characterized as near-surface lateral and deeper trailing indent type fractures (i.e., chatter marks). The SSD depth distributions are typically described by a single exponential distribution followed by an asymptotic cutoff in depth (c max ). The length of the trailing indent is strongly correlated with a given process. Using established fracture indentation relationships, it is shown that only a small fraction of the abrasive particles are being mechanically loaded and causing fracture, and it is likely the larger particles in the abrasive particle size distribution that bear the higher loads. The SSD depth was observed to increase with load and with a small amount of larger contaminant particles. Using a simple brittle fracture model for grinding, the SSD depth distribution has been related to the SSD length distribution to gain insight into 'effective' size distribution of particles participating in the fracture. Both the average crack length and the surface roughness were found to scale linearly with the maximum SSD depth (c max ). These relationships can serve as useful rules-of-thumb for nondestructively estimating SSD depth and to identify the process that caused the SSD. In certain applications such as high intensity lasers, SSD on the glass optics can serve as a reservoir for minute amounts of impurities that absorb the high intensity laser light and lead to subsequent laser-induced surface damage. Hence a more scientific understanding of SSD formation can provide a means to establish recipes to fabricate SSD-free, laser damage resistant optical surfaces.

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Section: Introductionmentioning

confidence: 99%

Sub-surface mechanical damage distributions during grinding of fused silica

Suratwala

Wong

Miller

et al. 2006

Journal of Non-Crystalline Solids

252

169

View full text Add to dashboard Cite

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“…It also gives information regarding the profile of the fractures moving from the surface into the bulk in addition to the maximum depth of damage in an optic that is at a particular point in the fabrication process. In contrast, other methods, such as the COM ball technique 9 , taper polishing method 10 , and more recently the MRF spot method 11 suffer from several disadvantages when used to quantitatively examine the statistical distribution of fractures on, or near, an optical surface. First, the interrogations may be restricted to small areas on the optic which limits the acquisition of sufficient information regarding the extent of fractures and SSD actually present over the entire surface.…”

Section: Introductionmentioning

confidence: 99%

“…This is particularly important on optics containing flaws that have been hidden beneath a layer of re-deposited and modified material (usually weakly-structured hydrated material) 9 . In this situation, buried SSD can pose a serious problem because of its interaction with the optic's surroundings and sources of activation such as shortwavelength, high-intensity monochromatic light 10 .…”

Section: Introductionmentioning

confidence: 99%

MRF applications: measurement of process-dependent subsurface damage in optical materials using the MRF wedge technique

et al. 2005

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Understanding the behavior of fractures and subsurface damage in the processes used during optic fabrication plays a key role in determining the final quality of the optical surface finish. During the early stages of surface preparation, brittle grinding processes induce fractures at or near an optical surface whose range can extend from depths of a few µm to hundreds of µm depending upon the process and tooling being employed. Controlling the occurrence, structure, and propagation of these sites during subsequent grinding and polishing operations is highly desirable if one wishes to obtain high-quality surfaces that are free of such artifacts. Over the past year, our team has made significant strides in developing a diagnostic technique that combines magnetorheological finishing (MRF) and scanning optical microscopy to measure and characterize subsurface damage in optical materials. The technique takes advantage of the unique nature of MRF to polish a prescribed large-area wedge into the optical surface without propagating existing damage or introducing new damage. The polished wedge is then analyzed to quantify subsurface damage as a function of depth from the original surface. Large-area measurement using scanning optical microscopy provides for improved accuracy and reliability over methods such as the COM ball-dimple technique. Examples of the technique's use will be presented that illustrate the behavior of subsurface damage in fused silica that arises during a variety of intermediate optical fabrication process steps.

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“…Manufacturing high fluence mirrors is particularly challenging for large-aperture laser systems such as the National Ignition Facility (NIF) with a beam aperture of 40 cm x 40 cm due to the high amount of surface area. [1][2] Specifically, the large-aperture NIF mirrors have a combined surface area of 460 m 2 of high-damage-threshold precision coatings on 100 tons of BK7. This optical surface area is equivalent to the combined surface area of eight Keck primary mirrors.…”

Section: Introductionmentioning

confidence: 99%

Engineering meter-scale laser resistant coatings for the near IR

et al. 2005

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Laser resistant coatings are needed for beam steering (mirrors), pulse switching (polarizers), and high transport efficiency on environmental barriers (windows / lenses) on large laser systems. A range of defects limit the exposure fluence of these coatings. By understanding the origin and damage mechanisms for these defects, the deposition process can be optimized to realize coatings with greater laser resistance. Electric field modeling can provide insight into which defects are most problematic. Laser damage growth studies are useful for determining a functional laser damage criteria. Mitigation techniques such as micro-machining with a single-crystal diamond cutting tool or short pulse laser ablation using the burst technique can be used to arrest growth in damage sites to extend optic lifetime.

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<title>The National Ignition Facility: the world's largest optics and laser system</title>

Cited by 63 publications

References 37 publications

Sub-surface mechanical damage distributions during grinding of fused silica

Sub-surface mechanical damage distributions during grinding of fused silica

MRF applications: measurement of process-dependent subsurface damage in optical materials using the MRF wedge technique

Engineering meter-scale laser resistant coatings for the near IR

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