ICMCTF 2022 Session B1-2-ThA: PVD Coatings and Technologies II

High-performance optical elements such as lenses and mirrors require high accuracy regarding figure error, waviness, and roughness. Furthermore, the complexity of surface shapes increases and an increasing demand for individually and complex shaped optical elements like non-standard aspheres, acylinders, or freeform elements is observed. In particular, the use of free-form elements in optical systems offers new functions in illumination and imaging applications and leads to fewer optical surfaces and thus more compact system designs. Recent advances in manufacturing technology are giving optical system designers more and more freedom. However, once the machinability of complex shaped surfaces is proven, tolerances become more stringent. Especially for scientific devices, e.g. space- and earth-based spectrometers or telescopes, or for laser beam shaping applications, high precision of free-form optical surfaces is required.

Depending on the material to be machined different non-conventional processing methods have been developed that are based either on atmospheric pressure reactive plasma jet etching or ion beam etching to deterministically remove material from the surface or for finishing.

Fluorine plasma jet-based methods are usually applied on materials like optical glasses, silicon, SiC or ULE. Here the specific chemical interactions between reactive radicals formed in the plasma and the surface constituents must be taken into account to achieve predictable results with respect to form accuracy, roughness, and laser damage threshold. The presentation gives an overview over different plasma jet based processing chains for precise freeform optical lens generation and finishing.

Ion beam etching technology has been recently shown to be applicable to aluminium surfaces. Increasing demands on applications of high-performance mirror devices for visible and ultraviolet spectral range call for new processing schemes. Reactively driven ion beam machining using oxygen and nitrogen gases allows direct figure error correction up to 1 μm machining depth while preserving the initial roughness. Machining marks originating from preliminary surface shaping by single-point diamond turning often limit the applicability of mirror surfaces in the short-periodic spectral range. Ion beam planarization with the aid of a polymeric sacrificial layer is shown as a promising process route for surface smoothing, resulting in successfully reduction of the turning mark structures. A combination with ion beam direct surface smoothing to perform a subsequent improvement of the microroughness is presented.

Magnetically-assisted inertial confinement fusion (ICF) could push current National Ignition Facility (NIF) implosions closer to ignition. The application of a pulsed magnetic field to an ICF target requires the development ofnew hohlraums, which are sphero-cylindrical canswith wall thicknesses of over about 10 µm made from heavymetals. Magnetized ICF targets require heavy metal hohlraums with an electrical resistivity of over 100 µΩ cm at cryogenic temperatures of about 20 K. Such requirements cannot be met by the Au and depleted U hohlraums traditionally used for ICF. Here, we present results of our systematic study by combinatorial direct-current magnetron co-sputtering, aimed at developing a family of binary Au-Ta and Au-Bi films with the microstructure, stress, mechanical properties, and electronic transport favorable for ICF applications.

This work was performed under the auspices of the U.S. DOE by LLNL under Contract DE-AC52-07NA27344.