The Laser Zentrum Hannover e.V. (LZH) carried out a two‑and‑a‑half year project (01 June 2020 – 31 December 2022) funded by the German Federal Ministry of Education and Research (grant 01QE2032B). The aim was to adapt rotary atomic‑layer deposition (rALD) for optical coatings, with a particular focus on the fabrication of optical diffraction gratings. rALD offers self‑limiting surface reactions that enable conformal coating of complex micro‑ and macro‑structures, a capability that conventional physical‑vapour deposition (PVD) techniques lack. By rotating the substrate, the rALD process achieves a deposition rate roughly 24 times higher than static ALD, improving throughput and economic viability.
The consortium comprised LZH, the rALD equipment manufacturer Beneq, the grating manufacturer Gitterwerk, and the university partner UniNe. LZH supplied its long‑standing expertise in optical coating design, deposition, and optical characterization. Beneq provided the first commercially available rALD system for the optical market, which was commissioned at LZH in January 2021 after a seven‑month delay caused by supply constraints and the COVID‑19 pandemic. Gitterwerk and UniNe supplied structured glass wafers and ion‑beam sputtered (IBS) reference layers, respectively. Together, the partners designed and fabricated holders for the structured wafers and performed absorption measurements on the IBS layers at LZH.
A key technical milestone was the integration of broadband monitoring (BBM) into the rALD system, enabling real‑time process control and precise layer deposition. With BBM, the team produced ultra‑low‑loss coatings: 3.1 ppm absorption for 186.2 nm Ta₂O₅ and 6.0 ppm for 1032 nm SiO₂, including the substrate. These values demonstrate that rALD can generate coatings with absorption comparable to the best conventional techniques while maintaining the conformality required for gratings. The system also allowed direct deposition of multilayer stacks without extensive pre‑development, further reducing process complexity.
The project proved that rALD can fully fill the trenches of diffraction gratings, a critical requirement for high‑efficiency devices. The ability to coat the entire grating structure uniformly opens the door to more robust, dust‑resistant gratings that retain performance over longer lifetimes, thereby expanding their applicability in ultrashort‑pulse laser systems and other demanding optical environments.
Scientific outputs include a 2023 Applied Optics paper titled “Enabling rotary atomic layer deposition for optical applications” and a 2022 SPIE proceedings article. A short project report was also published, summarizing the technical achievements and outlining future commercialization steps. The consortium’s work aligns with the Eurostars INTEGRA project (E! 113859), which seeks innovative grating technologies for ultrafast lasers.
In summary, the LZH‑Beneq‑Gitterwerk‑UniNe collaboration successfully demonstrated that rALD, enhanced with broadband monitoring, can produce ultra‑low‑absorption, conformal optical coatings on complex grating structures at industrially relevant speeds. The project’s results provide a clear pathway toward scalable manufacturing of high‑performance diffraction gratings for advanced laser applications.