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The use of beam-based technologies to process optical elements with nanoscale precision enables the fabrication of freeform surfaces. In particular, atmospheric pressure plasma jets (APPJs) have desirable properties, e.g., depth precision < 5 nm, low surface roughness and processing at atmospheric conditions. However, the composition of optical glasses and glass ceramics, containing metal oxides, leads to the formation of non-volatile reaction products that remain on the substrate surface. These residues reduce the etching rate and cause severe roughening of the surface. Laser irradiation has already been demonstrated as a promising option for removing the residual layer and the aim of the current work is to integrate it into the APPJ system for simultaneous processing. Therefore, an excimer laser (λ = 248 nm; tPulse = 20 ns) with a maximum pulse frequency of 100 Hz was added to a plasma jet setup and experiments with varying laser fluences as well as laser frequencies were performed on N-BK7 substrates. White light interferometry was used to analyse the samples. The experiments showed an improved etching result with higher removal rates for the combined process at high laser pulse frequency (100 Hz) and fluences in the range of 0.1-0.45 J·cm-2.

Mechanical cracks induced during grinding of brittle materials known as subsurface damage (SSD) reduce mechanical and optical properties of optical components. A characterisation of SSD is needed to guarantee a good quality and to optimize individual processes and processing chains. Current research focuses on non-destructive methods such as optical coherence tomography (OCT) to evaluate SSD depth and distribution and to replace currently established, but time-consuming and labour-intensive destructive methods. Yet the imaging of SSD remains challenging, even with high-resolution OCT providing a high sensitivity. The presented work proposes a combined measurement approach of enhanced SSD imaging by using a potassium hydroxide (KOH) wet etching process prior to OCT measurement. An etching process using 30% KOH at 80°C is applied and resulting etching rates are analysed. It is shown by an iterative etching experiment on optical glass SF6 that the KOH etching process enhances OCT signals of SSD under the surface, revealing up to 2.4-times deeper maximum SSD depths using an identical measurement setup.

To meet the ever-increasing user demand, eleven of the fifteen European Spallation Source (ESS) instruments under construction aim to offer polarised neutrons for user experiments. They include an imaging instrument, a SANS instruments, two reflectometers, three diffractometers, and four spectrometers. In conjunction with in-kind contributions and instrumentation grants, the ESS Polarisation Project will support the incorporation of polarisation analysis on eight of the eleven instruments. The project aims to deliver polarised neutrons for first-science experiments as instruments enter operation. Different polariser and polarisation analyser techniques will be available to accommodate the specifics of experiments on a given instrument. Polarised 3He neutron spin filter using either Metastable Optical Pumping (MEOP) or Spin-Exchange Optical Pumping (SEOP) techniques will provide shared-use equipment among many instruments, with SEOP’s main application being in situ beam-polarisation. Several instruments will also use polarising-supermirror devices. To provide wide-bandwidth spin-flipping capability to the time-of-flight instruments, Adiabatic Fast Passage (AFP) neutron spin flippers, also known as gradient-field radiofrequency spin flippers will be the main method of choice. Devices based on the same AFP principle will also be used to flip 3He nuclear spins. We are constructing our first 3He polariser setup, including field coils to produce highly uniform magnetic field. Monte Carlo simulations are being done for the supermirror polarisers. To ensure science-focused development, we are working with university partners in doing scientific experiments with polarised neutrons. These are some of the activities developing polarisation analysis for ESS instruments in our project.

Ultrashort pulse (USP) laser ablation is gaining popularity as a novel manufacturing technique for brittle materials, enabling the creation of complex freeform shapes that are challenging to produce with conventional optics manufacturing techniques. Freeforms have revolutionized optics manufacturing by providing designers with increased degrees of freedom using non-rotational symmetric components. However, this evolution presents new challenges for manufacturing processes, calling for innovative solutions such as USP ablation. To ensure the industrial viability of areal USP laser machining, it is crucial to not only consider material removal rates but also surface quality and subsurface damage (SSD). Especially for optical applications, harsh quality requirements must be met. This study investigates the SSD patterns of fused silica (FS) and borosilicate glass N-BK7 (BK) processed under different laser wavelengths, beam geometries and processing parameters using high-resolution optical coherence tomography (OCT). It is shown that OCT as non-destructive and 3D evaluation method is well-suited for analysing USP processes. The discovered differences in defect morphology between FS and BK emphasize the importance of selecting appropriate processes and process parameters when working with different materials. Compared to previous studies, for the parameter sets analysed here using OCT, much higher defects depths of up to 441 µm were revealed.

Freeform optical surfaces have become increasingly important in recent years, as they can be used to construct optical assemblies with a reduced number of optical surfaces compared to systems without freeform surfaces, and thus optical systems can get more compact and lighter. However, the flexible and efficient production of precise optical freeform surfaces poses a major problem. This manifests itself in insufficient precision of the optics, long delivery times and high prices. It is shown, that ultrasonic grinding processes, combined with an ultra-fine grinding process and subsequent plasma jet polishing, are very well suited for the production of freeform optics and have a high technical and economic potential. Therefore, the aim is to validate an industrially suitable process chain based on this combination, in order to produce freeform optics of high accuracy (shape deviations

Atmospheric pressure plasma jet machining technology not only provides a flexible and efficient way to generate and correct optical freeform surfaces made of fused silica, it can also be applied as a surface smoothing or polishing technique. Thermal plasma jet treatment leads to softening and redistribution of the material. An accurate temperature regime during the process is inevitable to achieve a uniformly smoothed surface. The possibilities for inȭprocess temperature control are demonstrated. Surface roughness values can be significantly reduced by a factor of 1000 depending on the initial roughness of the ground surface.