Silicon Dioxide Planarization| Impacts on Optical Coatings for High Energy Laser

<p> The work of this thesis is devoted to examining the impact of silicon dioxide (silica or SiO<sub>2</sub>) planarization on the optical properties and laser damage resistance of thin-film coatings. SiO<sub>2</sub> planarization is a process to smooth out fluence limi...

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Main Author: Day, Travis E.
Language:EN
Published: Colorado State University 2018
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Online Access:http://pqdtopen.proquest.com/#viewpdf?dispub=10690434
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spelling ndltd-PROQUEST-oai-pqdtoai.proquest.com-106904342018-03-01T16:00:05Z Silicon Dioxide Planarization| Impacts on Optical Coatings for High Energy Laser Day, Travis E. Engineering|Physics|Optics <p> The work of this thesis is devoted to examining the impact of silicon dioxide (silica or SiO<sub>2</sub>) planarization on the optical properties and laser damage resistance of thin-film coatings. SiO<sub>2</sub> planarization is a process to smooth out fluence limiting nodular defects within multilayer coatings for high-energy laser applications. Mitigating these defects will improve the power handling abilities and improve the lifetime of laser coatings. </p><p> Presented here is a combination of work with the aim of evaluating the optical and laser damage properties of SiO<sub>2</sub> planarization within single layers, bilayers, and multilayers. As compared to control (non-planarized) samples, a 2&ndash;3x increase in the thin-film absorption, which decreases with post-process annealing, was discovered for SiO<sub>2</sub> planarized samples. This suggests that planarization creates oxygen-related defects which can be annealed out and little impurity implantation. Investigations of laser damage resistance were carried out at &lambda; = 1030nm and pulse durations of &tau; = 220ps and 9ps. The laser damage of single and bilayer coatings is known to be dependent on the substrate-coating interface and this is further evidenced within this thesis. This is because the effects of planarization are masked by the extrinsic laser damage processes within the single and bilayers. Slight change (&lt; 15%) in the laser induced damage threshold (LIDT) at 220ps and 9ps was observed for planarized single and bilayers. Depending on coating design, post-process annealing was shown to increase the LIDT by ~10% to ~75% at 220ps and ~10% to ~45% at 9ps. Although the fused silica substrate surface LIDT was shown to follow the &radic;&tau; pulse scaling law for pulses above ~10ps, the single and bilayer coatings do not follow this pulse scaling. The divergence from the &radic;&tau; pulse scaling on the coatings suggests a variation in the laser damage initiation mechanisms between 220ps and 9ps. </p><p> Multilayer high-reflecting (HR) mirrors with varying planarization design were also damage tested. A 6&ndash;7 J/cm<sup>2</sup> LIDT, with 220ps, was observed for HR coatings with SiO<sub>2</sub> planarization layers within high electric-field areas within the coating. However, SiO<sub>2</sub> planarization at the substrate-coating interface, where the electric-field is minimal, and control (non-planarized) was shown to have a LIDT of 63 &plusmn; 1.2 J/cm<sup> 2</sup> and 21.5 &plusmn; 0.5 J/cm<sup>2</sup> for 220ps, respectively. At 9ps, the LIDT varied less than 90% difference between the various planarization designs. The substrate-coating planarization multilayer and control coating had an equal LIDT of 9.6 &plusmn; .3 J/cm<sup>2</sup> at 9ps.</p><p> Colorado State University 2018-02-27 00:00:00.0 thesis http://pqdtopen.proquest.com/#viewpdf?dispub=10690434 EN
collection NDLTD
language EN
sources NDLTD
topic Engineering|Physics|Optics
spellingShingle Engineering|Physics|Optics
Day, Travis E.
Silicon Dioxide Planarization| Impacts on Optical Coatings for High Energy Laser
description <p> The work of this thesis is devoted to examining the impact of silicon dioxide (silica or SiO<sub>2</sub>) planarization on the optical properties and laser damage resistance of thin-film coatings. SiO<sub>2</sub> planarization is a process to smooth out fluence limiting nodular defects within multilayer coatings for high-energy laser applications. Mitigating these defects will improve the power handling abilities and improve the lifetime of laser coatings. </p><p> Presented here is a combination of work with the aim of evaluating the optical and laser damage properties of SiO<sub>2</sub> planarization within single layers, bilayers, and multilayers. As compared to control (non-planarized) samples, a 2&ndash;3x increase in the thin-film absorption, which decreases with post-process annealing, was discovered for SiO<sub>2</sub> planarized samples. This suggests that planarization creates oxygen-related defects which can be annealed out and little impurity implantation. Investigations of laser damage resistance were carried out at &lambda; = 1030nm and pulse durations of &tau; = 220ps and 9ps. The laser damage of single and bilayer coatings is known to be dependent on the substrate-coating interface and this is further evidenced within this thesis. This is because the effects of planarization are masked by the extrinsic laser damage processes within the single and bilayers. Slight change (&lt; 15%) in the laser induced damage threshold (LIDT) at 220ps and 9ps was observed for planarized single and bilayers. Depending on coating design, post-process annealing was shown to increase the LIDT by ~10% to ~75% at 220ps and ~10% to ~45% at 9ps. Although the fused silica substrate surface LIDT was shown to follow the &radic;&tau; pulse scaling law for pulses above ~10ps, the single and bilayer coatings do not follow this pulse scaling. The divergence from the &radic;&tau; pulse scaling on the coatings suggests a variation in the laser damage initiation mechanisms between 220ps and 9ps. </p><p> Multilayer high-reflecting (HR) mirrors with varying planarization design were also damage tested. A 6&ndash;7 J/cm<sup>2</sup> LIDT, with 220ps, was observed for HR coatings with SiO<sub>2</sub> planarization layers within high electric-field areas within the coating. However, SiO<sub>2</sub> planarization at the substrate-coating interface, where the electric-field is minimal, and control (non-planarized) was shown to have a LIDT of 63 &plusmn; 1.2 J/cm<sup> 2</sup> and 21.5 &plusmn; 0.5 J/cm<sup>2</sup> for 220ps, respectively. At 9ps, the LIDT varied less than 90% difference between the various planarization designs. The substrate-coating planarization multilayer and control coating had an equal LIDT of 9.6 &plusmn; .3 J/cm<sup>2</sup> at 9ps.</p><p>
author Day, Travis E.
author_facet Day, Travis E.
author_sort Day, Travis E.
title Silicon Dioxide Planarization| Impacts on Optical Coatings for High Energy Laser
title_short Silicon Dioxide Planarization| Impacts on Optical Coatings for High Energy Laser
title_full Silicon Dioxide Planarization| Impacts on Optical Coatings for High Energy Laser
title_fullStr Silicon Dioxide Planarization| Impacts on Optical Coatings for High Energy Laser
title_full_unstemmed Silicon Dioxide Planarization| Impacts on Optical Coatings for High Energy Laser
title_sort silicon dioxide planarization| impacts on optical coatings for high energy laser
publisher Colorado State University
publishDate 2018
url http://pqdtopen.proquest.com/#viewpdf?dispub=10690434
work_keys_str_mv AT daytravise silicondioxideplanarizationimpactsonopticalcoatingsforhighenergylaser
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