Fusion ignition has been much more difficult than what was originally envisioned. Thanks to the progress on high-power laser engineering, the essential technologies with respect to design and construction of the MJ-level ICF driver in China have been mastered. Given that the loading capability is a bottle-neck challenge in both the construction and operation of ICF laser drivers, optics recycling based on improving the damage resistance of fused silica and mitigating the as-grown damage sites is currently the major strategy for improving the loading capability. Damage management for ICF laser drivers is challenging yet remains highly promising. This presentation introduces the essential techniques supporting the optical recycling strategy and the new materials and techniques developed to improve the loading capability of high-power laser facilities. The future laser drivers for ignition and high gain have significant features which include larger output energy, high manage asymmetry, stability and flexibility. Despite the obstacles to be faced with, we believe that fusion ignition with high gain will be success in the near future.

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High-power femtosecond lasers have become unbeatable tools for many areas of basic and applied research, and rapidly growing number of applications in industry and manufacturing. Good examples of the applications are the petawatt femtosecond laser facilities for inertial confinement fusion, ultrafast laser nanostructuring, and ultrafast table-top laser accelerators of elementary particles [1,2]. A majority of those applications require high levels of output laser power generated at the ultimate capabilities of a laser system. Progress of those applications substantially relies on ability to promote the ultimate levels of output power of the lasers. In a list of major limitations for output power of high-power laser system, laser-induced damage (LID) of multilayer optical coatings continues to occupy top positions [1-5] in spite of a tremendous improvement of LID thresholds of optical coatings over recent decades [2-6]. We briefly overview the major extrinsic mechanisms of LID including absorption by imperfections of film structure; localized field enhancement by scratches, nodular defects, and surface roughness; and local heating by absorbing micro- and nano-scale defects. Many of them are not compatible with the deterministic nature of LID by femtosecond laser pulses. In this connection, we pay major attention to intrinsic effects, e. g., contribution of intrinsic point defects to absorption and free-carrier generation and role of local field enhancement in optical coatings. We specifically focus on interface effects since interfaces between low-index and high-index layers continue to be of great concern as highly probable locations of damage initiators [3,5]. We also outline the major strategies to suppress the local field enhancement by modifications of coating design [3-5,7]. We then proceed with a critical review of the traditional models of ultrafast laser interactions with transparent materials of optical coatings relevant to intrinsic LID [8]. To be specific , we consider near-infrared laser pulses, which duration exceeds some 25 femtoseconds, but is short enough to dominantly initiate LID via laser-driven electron excitation, e. g., by free-electron generation. Illustrative estimations are done for a coating made from fused silica and hafnium dioxide. We identify the major gaps and contradictions of those models and discuss possible strategies to fix them. We also review some experimental data that have received unclear interpretation by the traditional models of ultrafast LID, e. g., formation of flat-bottom damage sites [5] and increase of LID thresholds in interface-free Rugate filters [3]. Based on our recent results, we discuss ultrafast laser-interface interactions and point out the effects missed by the traditional models, e. g., dynamic Schottky-type effect capable of inducing anomalous increase of absorption at the interfaces. Finally, we overview possible strategies to further improve LID thresholds of optical coatings. This work is based on research partly supported by Research Technology & Laboratory Directorate / Basic Research Office of the US Department of Defense via a Newton Award for Transformative Ideas during the COVID-19 Pandemic No. HQ00342010028 and ONR Award No. N00014-21-1-2395. [1] C. N. Danson, et al, High Power Laser Sci. Eng. 7, e54 (2019). [2] H. Qi, et al, High Power Laser Sci. Eng. 1, 36 (2013). [3] S. Dong, et al, Prog. Surf. Sci. 97, 100663 (2022). [4] J. Bellum, Optics and Photonics News, 28, June 2022. [5] C. J. Stolz, in Laser-Induced Damage in Optical Materials, D. Ristau, Ed., CRC Press, New York, 385 (2014). [6] C. J. Stolz, R. A. Negres, Opt. Eng. 57, 121910 (2018). [7] M. Zhu, et al, Light Sci. Appl. 9, 20 (2020). [8] M. Jupe, D. Ristau, in Laser-Induced Damage in Optical Materials, D. Ristau, Ed., CRC Press, New York, 411 (2014).

Dr. Vitaly Gruzdev received Honors MS degree in Optical Engineering and Devices in 1994 from Institute of Fine Mechanics and Optics (ITMO University), St. Petersburg, Russia. He received PhD in Optics in 2000 from Vavilov State Optical Institute, St. Petersburg, Russia. In 2001-2003 he was a visiting researcher with the group of Prof. Dr. D. von der Linde (University of Essen, Germany). In 2005 he joined the Department of Mechanical & Aerospace Engineering, University of Missouri in Columbia, Missouri, USA. Since 2019, Dr. Gruzdev is an Associate Research Professor with the Department of Physics and Astronomy, University of New Mexico (Albuquerque, New Mexico, USA). Theory and simulations of high-intensity ultrafast laser interactions with transparent solids, nonlinear absorption, photoionization, basic mechanisms of laser-induced damage, and ultrafast laser-surface interactions are his major areas of research interests and expertise. He has co-authored more than 150 publications including journal papers, papers in conference proceedings, three book chapters, and one US patent. In 2020, he was one of the 13 US scientists awarded with a Newton Award for Transformative Ideas during the COVID-19 Pandemic by Office of the Under Secretary of Defense for Research and Engineering and Basic Research Office at the US Department of Defense. He co-chaired Laser Damage Symposium (also known as Boulder Damage Symposium) from 2009 through 2022. He is a member of CLEO committee since 2020 and a co-chair of SPIE High Power Laser Ablation conference since 2022. From 2012 through 2022, he was a Guest Editor of six special sections of Optical Engineering on Laser Damage and two special section of JOSA B on laser-matter interactions. He is an Associate Editor of Optical Engineering since 2016. He is a Senior Member of Optica (former OSA) since 2016 and SPIE since 2021.