Defects Suppression in Process-Optimized High Power and Energy Multilayer Dielectric Coated Optics

Siping Qiu | 20-ERD-024

Project Overview

Multilayer dielectric (MLD) coatings are enabling components in high-power and high-energy pulsed laser systems. Currently, laser systems such as the Advanced Radiographic Capability (ARC) and National Ignition Facility (NIF) are often fluence-limited by the MLD coatings in the optical components, due to laser-induced damage. Such limitations hinder future utilization of lasers for applications under more extreme conditions, such as exposure to ns-pulses at 351 nm. Our previous work identified a class of nanoscale defects responsible for the laser performance degradation in MLD-coated optics, while other studies have shown that post-deposition treatments can lead to defect suppression in MLD coatings. What is needed is a fundamental understanding of how the various defects are suppressed or removed by post-deposition mitigation processes, to develop transformative technologies that would enable the manufacturing and fielding of MLD-coated optics tailored for extreme conditions.

This project utilized advanced characterization tools in conjunction with laser testing to understand the evolution of defects in ion beam sputtering (IBS)-produced MLD coatings, either through in-deposition process optimization or post-treatment processes. In the current project, we demonstrated that IBS-produced film by a heavy working gas showed much less gas entrapment, which effectively eliminates the source of plasma generation that would otherwise initiate laser damage. Furthermore, thermal annealing in a low-pressure, oxygen environment reduced the oxygen vacancies present in the films, and ps-laser conditions annihilated the low-fluence precursors, both of which led to improved thin-film laser performance. The acquired results provided new fundamental knowledge on the physics and chemistry of defects suppression in dielectric thin films and a new capability and enhanced institutional infrastructure for high-fluence MLD-coated optics fabrication.

Mission Impact

The research has developed science and technology tools and capabilities and provided essential results required to advance core missions in laser and optical science and technology and advanced materials and manufacturing. The development of post-deposition processes for manufacturing high-performance MLD-coated optics directly addresses ignition challenges by helping provide a pathway to higher power and energy on NIF and other ICF experimental facilities. These improved coatings also help extend the lifetime and performance of high-average-power pulsed laser systems for scientific applications such as the HAPLs. The project brought in and trained several postdocs who transitioned to early career staff at LLNL.

Publications, Presentations, and Patents

Mirkarimi, P. B., et al. 2022. "Improving the Laser Performance of Ion Beam Sputtered Dielectric Thin Films through the Suppression of Nanoscale Defects by Employing a Xenon Sputtering Gas." Optical Materials Express 12, no. 9: 3365-3378 (2022); doi: 10.1364/OME.462407. LLNL-JRNL-815116.

Peters, V. N., et al. 2021. "Investigation of UV, NS-Laser Damage Resistance of Hafnia Films Produced by Electron Beam Evaporation and Ion Beam Sputtering Deposition Methods." Journal of Applied Physics 130, 043103 (2021); doi: 10.1063/5.0053219. LLNL-JRNL-814837.

Qiu, S. R., et al. 2022. "Identifying, understanding, and suppressing of ns laser damage precursors in dielectric thin films." Keynote presentation, SPIE Laser Damage Program, Rochester September 2022. LLNL-PRES-839882.

Harthcock, C., et al., 2021. "Impact of film densification on UV-ns laser damage performance for MLD coatings." SPIE Laser Damage Program, Rochester October 2021. LLNL-PRES-826922.

Peters, V. N., et al. 2020. "Towards Understanding the Difference in Ultraviolet, NS-Laser Damage Resistance Between Hafnia Films Produced by Electron Beam Evaporation and Ion Beam Sputtering Methods." SPIE Laser Damage Program, Rochester September 2020; doi: 10.1117/12.2572814. LLNL-PRES-814293.

Harthcock, C., et al. 2020 "The Effort of Low Temperature Annealing on the UV, NS Laser Damage Performance of Hafnia Single Layers." SPIE Laser Damage Program, Rochester September 2020; doi: 10.1117/12.2572175. LLNL-PRES-814156.