Laser conditioning methods of hafnia silica multilayer mirrors

Stolz, Christopher J.; Sheehan, Lynn Matthew; Maricle, Stephen M.; Schwartz, Sheldon; Kozlowski, Mark R.; Jennings, Richard T.; Hue, Jean

doi:10.1117/12.311905

Cited by 12 publications

(8 citation statements)

References 8 publications

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“…• New laser glass compositions [21] , better glass property characterization [22][23][24][25][26][27][28][29] , advanced glass processing technology [30][31][32][33][34] and continuous optical glass melting methods [35] • Novel glass asphere and flat fabrication technologies using state-of-the-art deterministic figuring methods [5,36,37] • 10× faster KDP/DKDP crystal growth methods [38][39][40] with a better scientific understanding of the growth process [41][42][43][44][45][46] and novel high-capacity precision crystal finishing machines. • Laser damage resistant dielectric mirrors and polarizers manufactured to stringent multi-wavelength reflection and transmission specifications [7,10,11,[47][48][49][50][51][52][53][54][55] • Environmentally stable, laser damage-resistant, sol-gel anti-reflection coatings [14,[56][57][58][59] • Novel diffractive grating and continuous phase plate design and fabrication metho...…”

Section: Nif Vendors Advanced Materials and Manufacturing Methodsmentioning

confidence: 99%

“…The NIF mirrors and polarizers use HfO 2 /SiO 2 coatings for the main reason that they can be laser conditioned to increase the damage resistance. The laser conditioning has been shown to increase the damage threshold by 2 to 3× [6][7][8]53,[87][88][89][90][91] . In fact, laser conditioning is now an integral part of the optical production process and is simply treated as an added processing step; laser conditioning systems have been supplied to the coating vendors solely for this purpose.…”

Section: Improving Optics Lifetimementioning

confidence: 99%

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NIF optical materials and fabrication technologies: an overview

et al. 2004

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The high-energy/high-power section of the NIF laser system contains 7360 meter-scale optics. Advanced optical materials and fabrication technologies needed to manufacture the NIF optics have been developed and put into production at key vendor sites. Production rates are up to 20 times faster and per-optic costs 5 times lower than could be achieved prior to the NIF. In addition, the optics manufactured for NIF are better than specification giving laser performance better than the design. A suite of custom metrology tools have been designed, built and installed at the vendor sites to verify compliance with NIF optical specifications. A brief description of the NIF optical wavefront specifications for the glass and crystal optics is presented. The wavefront specifications span a continuous range of spatial scale-lengths from 10 µm to 0.5 m (full aperture). We have continued our multi-year research effort to improve the lifetime (i.e. damage resistance) of bulk optical materials, finished optical surfaces and multi-layer dielectric coatings. New methods for post-processing the completed optic to improve the damage resistance have been developed and made operational. This includes laser conditioning of coatings, glass surfaces and bulk KDP and DKDP and well as raster and full aperture defect mapping systems. Research on damage mechanisms continues to drive the development of even better optical materials.

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Section: Nif Vendors Advanced Materials and Manufacturing Methodsmentioning

confidence: 99%

Section: Improving Optics Lifetimementioning

confidence: 99%

NIF optical materials and fabrication technologies: an overview

et al. 2004

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“…A full-aperture mirror was also damage tested before and after solarization since small-aperture damage tests are not always representative of large-aperture damage thresholds. The optic was raster scanned over 25% of the area as described elsewhere 6 at fluences of 10, 14, 18, 20, 22, and 25 J/cm 2 . The damage threshold is defined as the fluence at which 300 µm or larger size damage is first detected.…”

Section: Laser Damage Thresholdmentioning

confidence: 99%

“…Previous experiments have validated that laser conditioning improves the damage threshold of electron beam coatings by 2 times. 6 The mirror was then solarized and rescanned at 18 J/cm 2 . No significant change was observed in the plasma scald density after solarization and raster scanning.…”

Section: Laser Damage Thresholdmentioning

confidence: 99%

Influence of BK7 substrate solarization on the performance on hafnia and silica multilayer mirrors

Stolz

Menapace

Génin

et al. 2003

Laser-Induced Damage in Optical Materials: 2002 and 7th International Workshop on Laser Beam and Optics Characterization

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Transport mirrors within the National Ignition Facility, a 192-beam 4-MJ fusion laser at 1053 nm, will be exposed to backscattered light from plasmas created from fusion targets and backlighters. This backscattered light covers the UV and visible spectrum from 351 -600 nm. The transport mirror BK7 substrates will be intentionally solarized to absorb >95% of the backscattered light to prevent damage to the metallic mechanical support hardware. Solarization has minimal impact on the 351-and 1053-nm laser-induced damage threshold or the reflected wavefront of the multilayer hafnia silica coating. Radiation sources of various energies were examined for BK7 darkening efficiency within the UV and visible region with 1.1 MeV gamma rays from a Cobalt 60 source ultimately being selected. Finally, bleaching rates were measured at elevated temperatures to generate a model for predicting the lifetime at ambient conditions (20°C), before solarized BK7 substrates exceed 5% transmission in the UV and visible region. Over a 30-mm thickness, BK7 glass will bleach in 10 years to 5% transmission at 600 nm, the most transmissive wavelengths over the 351-600 nm regions.

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“…[http://dx.doi.org/10.1063/1.4945687] Dielectric coatings are widely used as specific components to control the beam temporally or spatially in a high power laser system and generally processed by laser conditioning to improve the laser-induced damage threshold. [1][2][3] When irradiated by the 1053 nm ð1xÞ nanosecond laser, plasma scalds on the capping layer of dielectric coatings are characterized by surface discoloration due to the light scattering from nanoscale pin-holes within the scalding surface. 4 The coverage percentage of plasma scalds on the surface of optics is a crucial factor affecting the performance of optics through beam modulation or light scattering.…”

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confidence: 99%

Origin of the plasma scalds in dielectric coatings induced by 1ω laser

Wang

Zhao

et al. 2016

Applied Physics Letters

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The plasma scalds initiated by a 1053 nm (1ω) nanosecond laser are separated from the defect-induced damage pits, which is verified as a result of the ionization wavefront with the subnanosecond laser. Considering the beam reflection from solid-state absorption fronts during the damage process, a theoretical scalding threshold about 6.84 J/cm2 (12 ns) based on the energy required to start an air avalanche is evaluated and agrees well with the experimental scalding threshold. The occurrence order of the initial explosion and subsequent ionization wavefront is verified to explain most of the damage morphologies caused by the 1ω laser. In addition to the significance in laser conditioning or cleaning for a high-power laser system, the results also indicate that through the occurrence of plasma scalds it is possible to mark the onset time of air plasma during laser-coating interaction.

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Laser conditioning methods of hafnia silica multilayer mirrors

Cited by 12 publications

References 8 publications

NIF optical materials and fabrication technologies: an overview

NIF optical materials and fabrication technologies: an overview

Influence of BK7 substrate solarization on the performance on hafnia and silica multilayer mirrors

Origin of the plasma scalds in dielectric coatings induced by 1ω laser

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