With the rapid advancement of high-power laser technology, particularly in cutting-edge fields such as inertial confinement fusion (ICF), there is an increasing demand for optical coatings with high laser damage resistance. Using the wide-bandgap material SiO 2 for both the high-refractive-index (high- n ) and the low- n layer (dense and porous SiO 2 ) is a promising strategy to significantly enhance the laser-induced damage threshold (LIDT). However, conventional methods for preparing porous coating, such as sol-gel and glancing angle deposition, face challenges like severe cracking in multilayer structures and poor uniformity on large-aperture substrates.
In a new paper published in Light: Advanced Manufacturing , a research team led by Professor Jianda Shao and Professor Meiping Zhu from the Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, has developed a new approach based on selective chemical etching of mixture materials. First, an Al 2 O 3 –SiO 2 mixture coating is deposited using plasma-assisted electron-beam co-evaporation. Subsequently, a chemical etching process using an acid solution removes the Al 2 O 3 from the mixture, leaving behind a porous SiO 2 structure. By optimizing the mixing ratio and the etching solution, the etching efficiency is significantly improved.
Based on this method, the team successfully fabricated uniform porous SiO 2 monolayer coatings on large-scale fused silica substrates measuring 200 mm × 120 mm × 30 mm, achieving variations in refractive index and thickness of better than ±1%, thereby demonstrating demonstrates the feasibility of the approach for manufacturing large-size components. Furthermore, they designed and fabricated all-SiO 2 high-reflection and anti-reflection coatings. Both coatings exhibited absorption levels comparable to that of the fused silica substrate (~10 ppm) at 355 nm, along with excellent laser damage resistance. Notably, the LIDT of the anti-reflection coating reached 46.9 J/cm 2 , surpassing that of the fused silica substrate (41.1 J/cm 2 ).
This research proposes an all-silica ultraviolet laser coating based on a novel nanoporous material preparation method, which is suitable for the fabrication of large-scale multilayer ultraviolet laser coatings. This cost-effective and scalable approach opens new avenues for the design and fabrication of critical optical components for future high-power laser systems.
Light: Advanced Manufacturing
Advanced nanoporous SiO₂ coatings for ultraviolet laser-resistant high-reflection and anti-reflection optics