Engineering meter-scale laser resistant coatings for the near IR

Stolz, Christopher J.; Adams, John J.; Shirk, M. D.; Norton, Mary A.; Weiland, Timothy L.

doi:10.1117/12.625422

Cited by 9 publications

(3 citation statements)

References 27 publications

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“…The NIF laser contains approximately 7500 large optics [8][9][10][11][12][13][14][15][16][17][18]. These optics are sized depending on their incident angle for the 37 × 37 cm square aperture beams.…”

Section: National Ignition Facility Opticsmentioning

confidence: 99%

The National Ignition Facility: the path to a carbon-free energy future

Stolz

2012

Phil. Trans. R. Soc. A.

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The National Ignition Facility (NIF), the world's largest and most energetic laser system, is now operational at Lawrence Livermore National Laboratory. The NIF will enable exploration of scientific problems in national strategic security, basic science and fusion energy. One of the early NIF goals centres on achieving laboratory-scale thermonuclear ignition and energy gain, demonstrating the feasibility of laser fusion as a viable source of clean, carbon-free energy. This talk will discuss the precision technology and engineering challenges of building the NIF and those we must overcome to make fusion energy a commercial reality.

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Section: National Ignition Facility Opticsmentioning

confidence: 99%

The National Ignition Facility: the path to a carbon-free energy future

Stolz

2012

Phil. Trans. R. Soc. A.

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“…For example in the laser fusion apparatus at the National Ignition Facility (NIF) of Lawrence Livermore National Laboratories (LLNL), any external reflections or scattered light from the lasing windows or system lenses, gratings, and debris shields, adds spatial noise to the beam, limiting the ability of the system to focus enough power onto the target gas-filled pellets [1][2][3] . In other medical and industrial laser-based tools, reflected light can damage sensitive equipment such as imaging detectors or even components of the laser source itself such as pump laser diodes.…”

Section: Introductionmentioning

confidence: 99%

High laser damage threshold surface relief micro-structures for anti-reflection applications

Hobbs

MacLeod

2007

SPIE Proceedings

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Microstructures built into the surfaces of an optic or window, are an effective replacement for thin-film coatings in antireflection (AR) and narrow-band filter applications. AR microstructures exhibit particularly noteworthy performance where an average reflection loss of less than 0.2% over a four-octave range (400-1800nm) has been demonstrated, and a loss of less than 0.03% is routinely achieved for narrow-band applications. Because AR micro-textures provide a gradual change in the refractive index at a material boundary, it is expected that light can propagate through the boundary without material damage at energy levels that are much higher than that found with thin-film interference coatings. Recently, it was shown that the laser induced damage threshold (LIDT) of an inexpensive borosilicate glass window containing AR microstructures was nearly 57 J/cm2 at 1064nm (20ns pulse). This LIDT is two to three times greater than the damage threshold of single-layer sol-gel AR coatings on fused silica often reported in the literature.The development of surface relief AR textures for use in high-energy laser applications is presented. Data from scanning electron microscope (SEM) analysis, reflection measurements, and LIDT testing, is shown for high performance AR microstructures fabricated in fused silica, and borosilicate glass. Results of LIDT testing at wavelengths ranging from the near ultraviolet through the near infrared confirm the initial result that AR microstructures can operate at pulsed laser power levels at least two times higher than thin-film coatings. For near infrared applications such as laser weapons and fiber optic communications requiring high performance AR, LIDT levels for AR microstructures in fused silica are found to be at least five times greater than conventional multi-layer thin film coatings. An initial surface absorption test at 1064nm shows that AR microstructures may also exhibit improved lifetimes within continuous wave laser systems.

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“…[1-2] Moreover, a recent study has shown that substrate scratches and impurities generated from surface finishing of the BK7 substrate can also lead to laser-induced damage on the multilayer coating. [3][4] Substrate scratches on the optic surface are inevitably created during the final shaping of the component through abrasive cutting, grinding and final polishing. Earlier studies have shown that substrate scratches on fused silica substrates act as precursors and lead to laser damage by inducing sub-bandgap absorption [5][6] which can be reduced by chemical etching of the substrate to improve optic performance.…”

Section: Introductionmentioning

confidence: 99%

Impact of substrate surface scratches on the laser damage resistance of multilayer coatings

et al. 2010

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Substrate scratches can limit the laser resistance of multilayer mirror coatings on high-peak-power laser systems. To date, the mechanism by which substrate surface defects affect the performance of coating layers under high power laser irradiation is not well defined. In this study, we combine experimental approaches with theoretical simulations to delineate the correlation between laser damage resistance of coating layers and the physical properties of the substrate surface defects including scratches. A focused ion beam technique is used to reveal the morphological evolution of coating layers on surface scratches. Preliminary results show that coating layers initially follow the trench morphology on the substrate surface, and as the thickness increases, gradually overcoat voids and planarize the surface. Simulations of the electrical-field distribution of the defective layers using the finite-difference timedomain (FDTD) method show that field intensification exists mostly near the top surface region of the coating near convex focusing structures. The light intensification could be responsible for the reduced damage threshold. Damage testing under 1064 nm, 3 ns laser irradiation over coating layers on substrates with designed scratches show that damage probability and threshold of the multilayer depend on substrate scratch density and width. Our preliminary results show that damage occurs on the region of the coating where substrate scratches reside and etching of the substrate before coating does not seem to improve the laser damage resistance.

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Engineering meter-scale laser resistant coatings for the near IR

Cited by 9 publications

References 27 publications

The National Ignition Facility: the path to a carbon-free energy future

The National Ignition Facility: the path to a carbon-free energy future

High laser damage threshold surface relief micro-structures for anti-reflection applications

Impact of substrate surface scratches on the laser damage resistance of multilayer coatings

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