Relatively thick (>1-um) organic-polymer coatings with a large resistance to laser-induced damage at UV wavelengths are desired for new inertial confinement fusion laser optics under development at the Laboratory for Laser Energetics. These optics include surface-figured, KDP polarization rotators and actively cooled laser glass. Organic-polymer materials, however, are generally known to have a low laser-induced–damage threshold (LIDT) in the UV, particularly as it pertains to multipulse applications. In this work, we present the single-pulse and multipulse LIDT results for thick (>1.5-um) polymethacrylate films deposited on fused silica and cured at different temperatures. The results demonstrate that it is possible for thick polymer films to withstand thousands of pulses at fluences higher than their single-pulse LIDT counterpart. In fact, in some test sites, the underlying fused silica substrate suffered exit surface damage before the polymer film could be damaged. These results and a discussion of the underlying mechanisms responsible for this behavior will be presented.
The near-infrared, laser-induced damage performance of a broadband, antireflective metasurface optic was measured at five different pulse durations, ranging from 1.4 ns to 20 fs. Analogous measurements were performed on an equivalent bare fused silica substrate which did not receive metasurface treatment. Results showed that the damage threshold of the metasurface was about 30% to 50% of the first-surface damage threshold of the untreated substrate (exit-surface damage was not considered). The resulting morphologies are investigated with scanning electron microscopy. The goal of this work is to investigate the feasibility of metasurface optics in short-pulse, high-peak-power laser applications.
The 2023 Laser Damage conference thin-film damage competition was devoted to a survey on the state-of-the-art broadband near-IR multilayer dielectric (MLD) mirrors designed for ultra-short pulsed laser applications. The requirements for the coatings were a minimum reflection of 99.5% at 45-deg incidence angle for S-polarization from 830 nm to 1010 nm and group delay dispersion (GDD) <±50 fs2. The participants were allowed to select the coating materials, coating design, and coating deposition method. Samples were damage tested at a single testing facility to enable direct comparison among the participants using a 25±5 fs optical parametric chirped-pulse amplification (OPCPA) laser system operating at 5 Hz. The testing results from this set of 37 samples showed that dense coatings by ion-beam sputtering (IBS), magnetron sputtering (MS), and electron-beam ion assisted deposition (e-beam IAD) exhibited highest damage initiation onset (laser-induced damage threshold or LIDT) while e-beam coatings were low performers. In addition, multilayer coatings using tantala and/or hafnia as high index materials were top performers. Furthermore, this competition included for the first time the measurement of the damage growth onset (laser-induced damage growth threshold or LDGT). This latter performance metric plays an important role in establishing the safe operational conditions for larger aperture ultrashort pulsed lasers. Information pertaining to the morphology of the damage sites and their evolution under subsequent exposure to different laser fluences leading to damage growth is presented. Finally, not all coating samples in the survey met the GDD requirements stated above and associated measurements are discussed in the context of the present and past thin-film damage competitions focused on similar broadband near-IR MLD coatings.
This year’s competition proposed to survey the state-of-the-art broadband, near-IR multilayer dielectric (MLD) mirrors designed for ultra-short, pulsed laser applications. The requirements for the coatings were a minimum reflection of 99.5% at 45-degree incidence angle for S-polarization from 830 nm to 1010 nm and group delay dispersion (GDD) < ± 50 fs2. The participants in this effort selected the coating materials, coating design, and deposition method. Samples were damage tested at a single testing facility to enable direct comparison among the participants using a 25 ± 5 fs OPCPA laser system operating at 5 Hz. A double blind test assured sample and submitter anonymity. The damage performance results, sample rankings, details of the deposition processes, coating materials and substrate cleaning methods are shared here. We found that multilayer coatings using tantala and/or hafnia as high index materials were top performers within several coating deposition groups. Specifically, dense coatings by ion-beam sputtering (IBS), magnetron sputtering (MS), and electron-beam ion assisted deposition (e-beam IAD) exhibited highest damage initiation onset (LIDT) while e-beam coatings were low performers. In addition, damage growth onset (LDGT) was also examined and the results are reported here for all samples as this performance metric plays an important role in establishing the safe operational conditions for larger aperture, ultrashort pulsed lasers. Lastly, not all coating samples in the survey met the GDD requirements stated above and associated measurements are discussed in the context of the present and past competitions focused on similar broadband, near-IR MLD coatings.
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