Anti-reflective metal surfaces on materials with large band gaps

Project description

Laser inertial fusion is a promising option for securing a clean, resource-efficient, and practically inexhaustible energy supply for the future. In laser inertial fusion, high-precision, high-energy laser beams are used to compress and heat fuel capsules, causing the atomic nuclei to fuse and releasing large amounts of energy. In order to strike the fuel capsule evenly and ensure symmetrical compression, the laser beams must be aligned with extreme precision and optical losses due to reflection must be minimized. Finally, the high energy of the laser causes thermal expansion, which varies depending on the material properties and can cause cracks or other damage, thereby negatively affecting the precision and service life of the equipment. This, too, must be minimized.

The “nanoAR” project aims to develop nanostructured and porous anti-reflective coatings (so-called “moth-eye structures”) from materials with a high band gap in order to ensure the laser radiation resistance of the optical components. In addition, a subtractive approach is being pursued in which lenses made of a single material are to obtain the desired anti-reflective properties through suitable nanostructuring of the surface. Innovative etching processes for structuring curved surfaces are also being developed in order to realize customized anti-reflective structures that remain stable over a broad wavelength range from UV to near infrared.

Specifically, the project is pursuing two groundbreaking approaches:

1. Development of a new reactive ion etching (RIE) process: By using customized grid electrodes adapted to the geometry of the lens substrates, homogeneous etching is to be achieved even on strongly curved surfaces.
2. Optimization of reactive ion beam etching (RIBE) processes: Intermediate masks will be used to enable stable structure transfers onto lens substrates.

Using the example of two materials with a large band gap (quartz glass and calcium fluoride), corresponding demonstrators with large areas are to be developed for different wavelengths and pulse lengths – from the UV range (351 nm) to the visible spectral range and near infrared (NIR, 1,053 nm). 

Fraunhofer IWM subproject:

Modeling the influence of a large heat input on a-SiO2 glass using molecular dynamics simulation. Structural analysis of the defects created in the model structures and calculation of the corresponding defect levels in the band gap using density functional theory (DFT-1/2) and DFTB. This knowledge about the defects allows strategies to be developed for possible repair, e.g., through hydrogen or heat post-treatment.