New and robust anti-reflective solutions for laser inertial confinement fusion

Laser fusion power plants will be the basis for a clean energy source of the future. In order for these to work efficiently and reliably in the future, laser technologies must be available that meet the requirements for high performance and continuous operation.
As part of the funding program “Basic technologies for fusion – on the way to the fusion power plant”, the Federal Ministry of Education and Research (BMBF) is funding the joint project “nanoAR” with six million euros.
In this new research project, nine project partners from industry and research are working on methods for the prevention of near-surface damage and structural reflection reduction of the optical components used. Their approaches could also be transferred to other fields of application for high-performance optics.
In laser inertial confinement fusion, high-precision and high-energy laser beams are used to compress and heat fuel capsules. The temperature and pressure in the capsules increase to such an extent that atomic nuclei fuse. This process releases a large amount of energy. If the amount of energy gained is greater than the energy expended, laser inertial confinement fusion can be a valuable source of clean energy for the future.

Novel antireflection coatings and structures are intended to optimize laser beam guidance

The laser beams must be extremely precisely aligned in order to hit the fuel capsule evenly and ensure symmetrical compression. Their path is guided through various materials and atmospheres. This leads to optical losses, which are higher the more lenses are used. Energy is also lost when the laser beam hits the fuel capsule because its material reflects some of the energy, as well. Last but not least, the high energy of the laser causes thermal expansion, which varies depending on the material properties of state-of-the-art anti-reflective coatings and can lead to cracks or other damage and thus negatively affect the precision and service life of the systems. The project partners are therefore going to substitute anti-reflective coatings by anti-reflective structures machined out of the lens.

Combination of anti-reflective coating and nanostructured materials

Instead of a combination of a substrate material and several layers of material applied for anti-reflective coating, the project partners are relying on nanostructures on the surface od the lenses. By the use of different etching processes, the lenses should get the desired anti-reflective properties. Using the example of quartz glass and calcium fluoride, two materials with a large band gap, corresponding demonstrators with large surfaces are to be developed for different wavelengths and pulse lengths.

Glatt’s part in this project relates to the production of ultra-fine nanopowders with high purity and a narrow particle size distribution. Glatt powder synthesis will be used for this purpose. The powders produced will then be applied by the project partners as a mask to the surfaces to be anti-reflective coated. In the subsequent etching process, the shading by the particles causes the formation of the desired surface structure. To ensure that the particles are distributed as evenly as possible on the surface, the powders should also be coated to prevent agglomeration. In addition to powder synthesis, a powder CVD process is to be used for this purpose.

The project team wants to prove that the approach can be optimized with a structural anti-reflection coating specifically for high-power laser applications such as laser inertial confinement fusion and achieve the best possible anti-reflection effects below 0.5 percent residual reflection.

Partners from industry and research in the “nanoAR” project

In the “nanoAR” project, the project partners are pooling their expertise in manufacturing and processing methods for the effective reduction of sub surface damage, technology-open process development for nanostructure generation, including the use of simulations and modeling, as well as high-resolution material characterization and the development of new methods for quality assurance.

Participants in the project “Anti-reflective metasurfaces on materials with a large band gap (nanoAR)” are Glatt Ingenieurtechnik GmbH (Weimar), POG Präzisionsoptik Gera GmbH (Löbichau), FLP Microfinishing GmbH (Zörbig), Trionplas Technologies GmbH (Leipzig), the Fraunhofer IOF (Jena), the Fraunhofer IMWS (Halle/Saale), the Fraunhofer Institute for Mechanics of Materials IWM (Freiburg), the Leibniz Institute for Surface Modification IOM (Leipzig) and the Ernst Abbe University of Applied Sciences (Jena).

Scientific contacts:
Dr. Viktor Drescher, Product Manager Thermal Powder Synthesis, Glatt Ingenieurtechnik GmbH

Further information: Anti-reflective metasurfaces on materials with a large band gap – Glatt in the collaborative project “nanoAR”

See also: New and robust anti-reflective solutions for laser inertial fusion for the clean energy supply of the future (source: Fraunhofer IOF)

Further joint projects in which Glatt is involved: R&D projects. Glatt Ingenieurtechnik