Substrate-engraved antireflective nanostructured surfaces for high-power laser applications

Journal Article · Tue May 12 00:00:00 EDT 2020 · Optica

DOI:https://doi.org/10.1364/OPTICA.391217· OSTI ID:1618004

Ray, Nathan J. ; Yoo, Jae-Hyuck ; Nguyen, Hoang T.; Johnson, Michael A.; Elhadj, Selim; Baxamusa, Salmaan H.; Feigenbaum, Eyal

A critical component for all high-power laser systems that is particularly susceptible to laser damage is the antireflective coating, which maximizes energy transmission and minimizes scattered and stray light. We demonstrate the ability to generate substrate-engraved nanostructured surfaces (NS) for scalable and designable antireflective (AR) coatings that are monolithic to the substrate and can handle peak power levels comparable to the bulk material. Experimentally measured reflectance from these fabricated structures has validated our effective index theory-based transmission matrix model, demonstrating the designability of the AR properties. Upon exposure to sufficiently high fluences, a new mode of damage, nanostructured surface damage, has been observed and is likely the result of thermally driven material reflow accompanied by plasma initiation on the nanostructured surface. At 1053 nm, nanostructured surface damage onsets at 39 J/cm² with sample cleaning and 74 J/cm² after laser conditioning—very close to the reference substrate at 81 J/cm². At 351 nm we show damage onset of 30 J/cm², with reference substrate material damage onset of 47 J/cm². Therefore, damage is close to the bulk material and represents an improvement with respect to other methods. The nanostructured surfaces were found to be mechanically durable and able to withstand cleaning procedures with sonication. Under normal incidence mechanical testing with a 200 µm radius indenter tip, the AR performance of these nanostructured surfaces was minimally impacted at pressures orders of magnitude higher than an average fingerprint pressure—indicating that incidental handling contact will not affect NS structures. Mechanical damage is attributed to plastic compression, not fracturing of the NS features. We demonstrate for the first time, to the best of our knowledge, that NS AR coatings, despite being rich in etched surface features, can tolerate laser fluences comparable to unprocessed optical surfaces. Furthermore, laser-damage features of NS indicate a unique non-growing failure mode whereby following absorption the featureless damage site does not precipitate future damage growth, reducing considerably the burdens for managing optics processing in high-power laser systems.

• Research Organization: Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
• Sponsoring Organization: USDOE National Nuclear Security Administration (NNSA); USDOE Laboratory Directed Research and Development (LDRD) Program
• Grant/Contract Number: AC52-07NA27344; 18-ERD-005
• OSTI ID: 1618004
• Alternate ID(s): OSTI ID: 1722963
• Report Number(s): LLNL-JRNL-805293
• Journal Information: Optica, Journal Name: Optica Vol. 7 Journal Issue: 5; ISSN 2334-2536
• Publisher: Optical Society of America
• Country of Publication: United States
• Language: English

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