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In a conducting medium held at finite temperature, free carriers perform Brownian motion and generate fluctuating electromagnetic fields. In this paper, an averaged Lorentz force density is computed that turns out to be nonzero in a thin subsurface layer, pointing towards the surface, while it vanishes in the bulk. This is an elementary example of rectified fluctuations, similar to the Casimir force or radiative heat transport. The results obtained also provide an experimental way to distinguish between the Drude and so-called plasma models.

This paper deals with double-pulse laser-induced breakdown spectroscopy (LIBS) underwater, which is a promising analytical method for elemental analysis in the deep sea up to a water depth of 6000 m. A double-pulse laser with a wavelength of 1064 nm is used, which provides a pulse energy of up to 266 mJ for each laser pulse (in single pulse mode), a pulse width of 5–7 ns and a pulse delay in the range of 0.5 to 20 µs. In the double-pulse LIBS method, the first laser pulse creates a cavity on the material surface, and then the second laser pulse forms the plasma in this cavity. It is expected that the plasma is affected by the cavity’s size and lifetime. For this reason, the influence of focus position, pulse energy and pulse delay on the cavity and plasma formation at shallow water depth has been investigated.

Identifying/classifying damage features on soft materials, such as tissues, is much more challenging than on classical, hard materials—but nevertheless important, especially in the field of bio-tribology. For instance, cartilage samples from osteoarthritic patients exhibit surface damage even at early stages of tissue degeneration, and corneal tissues can be damaged by contact lenses when the ocular lubrication system fails. Here, we employ unsupervised machine learning (ML) methods to assess the surface condition of a soft tissue by detecting and classifying different wear morphologies as well as the severity of surface damage they represent. We show that different clustering methods, especially a k-means clustering algorithm, can indeed achieve a—from a material science point of view—meaningful classification of those tissue samples. Our study pinpoints the ability of unsupervised ML models to guide or even replace human decision processes for the analysis of complex surfaces and topographical datasets that—either owing to their complexity or the sample size—exceed the capability of the human brain.

A new concept for polishing pads for flat and spherical surfaces is introduced which comprises additive manufactured polishing pads made of cerium oxide. By using additive manufacturing technologies, polishing processes with polishing slurry can be substituted with tools containing bonded grain. The bonded polishing pads can be fabricated using rolling processes. The pad geometries can be adjusted by using laser cutting. Furthermore, surface modifications of the pad can be applied with laser processes to favour quality and economic factors of the polishing procedure. First results from the experimental setup are showing, that lapped surfaces with a roughness Rq of ~ 500 nm can be improved to approx. Rq = 30 nm roughness by polishing with bonded grain cerium oxide foils. Further approaches for future investigations and applications are proposed.

The flexible and efficient production of precise optical free-form surfaces requires advanced kinematic operating principles. Due to the complex surface geometries, polishing processes with point or linear contact are used. These generally result in longer polishing times due to the smaller footprint compared to large-area polishing tools. The creation of a high precision, polishable surface in the shaping steps of the process chain is therefore of great importance. This applies in particular to minimising the roughness, but also the depth of SSD (sub-surface damage) and the mid-spatial frequency errors before the polishing process. The article describes selected process chains for the production of free-form optics and presents options for optimising the required polishing steps.

To prevent the disposal of minimally damaged lenses that fall outside the acceptable scratch and dig tolerance levels, an experimental study was conducted to repair mechanical scratches on a fused silica surface. The scratches were created using a diamond tip and then repaired using a CO2 laser. Various loads on the diamond lip and laser output power were tested. The transmission changes and subsurface damages were analysed. The surface quality analysis was performed using a white light interferometer, while the subsurface damage analysis was performed using optical coherence tomography. Local absorption differences can be quantified using photothermal deflection. To significantly enhance local transmittance, brittle and ductile scratches of various depths have been successfully healed.

Due to the increasing demands and complexity of optical glass components to be processed in the future, advanced technologies and precision machining methods will be required in order to produce high-quality optics economically. The polyjet process enables the production of 3D printed gradient index (GRIN) polishing tools with hardness gradients by combining different polymer materials for e.g. synchrospeed polishing. In terms of their geometric design, these tools are significantly more flexible than conventional ones, where the polishing cloth must be glued to metal tool holders. The composition of the polishing pad material directly influences the process efficiency and quality at which the glass is polished. In a laboratory test the influence of the mechanical properties of the multi-material pads on process efficiency, i.e. their long-term stability and the polishing rate of the glass workpiece is demonstrated.

The manufacturing of optical components is subject to constant efforts to optimise production processes in order to achieve high surface qualities under the most economical conditions possible. This includes the refinement of existing technologies or development of completely new production technologies. One possible approach is the combination of conventional machining processes for optical components like diamond turning, grinding or polishing with laser-based processes to thermally influence the surface for improved machining or surface properties. For this, knowledge of the thermal interactions of the laser on the component surface is needed, which in turn requires its metrological acquisition. In this work, measurements were carried out using various methods for the controlled heating of glass surfaces by an infrared laser (λ=1070 nm). Among other things, a clear correlation between the samples surface roughness and the laser absorption is found.

With big datasets and highly efficient algorithms becoming increasingly available for many problem sets, rapid advancements and recent breakthroughs achieved in the field of machine learning encourage more and more scientific fields to make use of such a computational data analysis. Still, for many research problems, the amount of data available for training a machine learning (ML) model is very limited. An important strategy to combat the problems arising from data sparsity is feature elimination—a method that aims at reducing the dimensionality of an input feature space. Most such strategies exclusively focus on analyzing pairwise correlations, or they eliminate features based on their relation to a selected output label or by optimizing performance measures of a certain ML model. However, those strategies do not necessarily remove redundant information from datasets and cannot be applied to certain situations, e.g., to unsupervised learning models. Neither of these limitations applies to the network-based, correlation-driven redundancy elimination (NETCORE) algorithm introduced here, where the size of a feature vector is reduced by considering both redundancy and elimination efficiency. The NETCORE algorithm is model-independent, does not require an output label, and is applicable to all kinds of correlation topographies within a dataset. Thus, this algorithm has the potential to be a highly beneficial preprocessing tool for various machine learning pipelines.

Abstract The plasma diagnostics presented in this article target the plasma surrounding a spacecraft that is created by the electric thruster and its surface modifying effects. The diagnostic package includes a retarding potential analyzer, a plane Langmuir probe, and an erosion sensor. The paper describes the instrument as well as suitable test environments for mimicking the effects expected in space and shows test results. The system is to fly for the first time on the Heinrich Hertz satellite, which is scheduled to be launched in 2023. The spacecraft will be equipped with a pair of Highly Efficient Multistage Plasma Thrusters (HEMPT) and a pair of Hall thrusters for redundancy.

When two initially thermal many-body systems start to interact strongly, their transient states quickly become non-Gibbsian, even if the systems eventually equilibrate. To see beyond this apparent lack of structure during the transient regime, we use a refined notion of thermality, which we call g-local. A system is g-locally thermal if the states of all its small subsystems are marginals of global thermal states. We numerically demonstrate for two harmonic lattices that whenever the total system equilibrates in the long run, each lattice remains g-locally thermal at all times, including the transient regime. This is true even when the lattices have long-range interactions within them. In all cases, we find that the equilibrium is described by the generalized Gibbs ensemble, with three-dimensional lattices requiring special treatment due to their extended set of conserved charges. We compare our findings with the well-known two-temperature model. While its standard form is not valid beyond weak coupling, we show that at strong coupling it can be partially salvaged by adopting the concept of a g-local temperature.

The long-time behaviour of spin-spin correlators in the slow relaxation of systems undergoing phase-ordering kinetics is studied in geometries of finite size. A phenomenological finite-size scaling ansatz is formulated and tested through the exact solution of the kinetic spherical model, quenched to below the critical temperature, in 2< d < 4 dimensions.

The development or the improvement of production processes are necessary aspects, in order to enhance the quality and efficiency in optical manufacturing. This paper presents an approach to manufacture fine grinding tools in a very flexible and efficient way. A new filament composed of polyamide, ZrO2 particles and diamond grains is developed and used in an additive manufacturing process for tool fabrication. The resulting tools are successfully applied in an ultra-fine grinding process on fused silica samples.

The presented investigations build on the results already presented at EOSAM 2022 on the in-situ monitoring of grinding processes, in which high correlations between vibrometry, force and topography data of machined fused silica samples could already be proven. With the help of new measurement setups, it was possible to also detect high-frequency vibration components in CNC grinding processes and to check their effects on the resulting surface qualities. The investigations were carried out on a 5-axis CNC machine and monitored with the help of vibrometric and white-light interferometric measurement technology. The aim was to look at the influences of process-side parameters on the process vibrations and the resulting surface qualities.

In many conventional optical manufacturing processes, lapping is still a standard method to provide polishable surfaces. With the increasing use of CNC technology, efforts are being made to substitute the lapping process in the process chain. The paper presents studies that compare the lapping and fine grinding processes and provide an assessment of the subsequent polishing process. By using fine grinding with resin bond tools, polishing times can be significantly reduced and subsurface damage structures minimized. Ultra-fine grinding is also an important shaping process for the production of complex surface geometries, such as free-form optics.

A new concept for synchro-speed polishing of flat and spherical surfaces is introduced: 3D printed gradient index (GRIN) polishing tools. By using additive manufacturing technologies in combination with photopolymer plastics, GRIN tools can be fabricated that are individually adapted to the workpiece geometry. By using two different plastics, the hardness and therefore the removal rate of certain tool areas can be defined. Surface structures, benefiting material removal rate and tool wear rate, are possible as well as lightweight structures with high mechanically stability. Tools can be fabricated as thin foils as well as solid pads, ranging from small (few mm) to large diameters. Additionally, the pads can be fabricated with an individual radius. This can enable the replacement of radius-dependent tool holders, because the pads can be mounted on flat tool interfaces, since the radius is not dependent from the tool body anymore. First results from the experimental setup are showing, that by using GRIN foils similar surface quality results can be achieved in comparison to conventional polyurethane foils, while the GRIN foils are offering a lot more possibilities regarding process optimization.

Silver nanoparticles (AgNPs) show an extraordinary strong interaction with light, which enables confinement and field enhancement at the nanoscale. However, despite their localized nature, such phenomena are often sought to be exploited on a larger device length scale, for example, in sensors, solar cells, or photocatalytic cells. Unfortunately, this is often limited by strong absorption. One way to reduce these losses is to first focus light with low loss dielectric optics and then to place the AgNPs in that focus. Here, we present a clear experimental proof that growth of AgNPs from the liquid phase at a substrate surface can be controlled by light. Violet light of 405 nm and 1.5 W/cm2 is coupled into thin film resonators and locally focused at their surface. The AgNPs grow at the focus position with sub-Abbe alignment accuracy. Numerical simulations confirm that this alignment causes an increased field enhancement within the AgNPs and is therefore expected to lead to an improved performance of the resulting hybrid devices.

The growing interest in providing additional degrees of freedom to the design of high-end optical systems has led to an increased demand for freeform optical elements. The efficient fabrication of such elements requires a polishing process that provides high removal rates and a stable removal function while working with a relatively small spot size. Taking these constraints into consideration this paper focuses on the successful implementation of polishing processes applying the A-WPT (Advanced Wheel Polishing Tool) technology. Addressing the requirements regarding its removal characteristics as mentioned before, it represents an appropriate choice for providing an efficient pre-polishing as well as corrective polishing technique. In order to maintain perpendicularity towards the freeform surface to be polished, the A-WPT is run on a 5-axis simultaneous machining system. First investigations of the achieved surface accuracy after pre-polishing were carried out as well as an assessment of residual surface features within different spatial frequency regions. In addition, the polished surface is being checked for remaining SSD using an OCT technique.

The presented investigations deal with real-time evaluation and recording of vibrations and forces during a CNC grinding process, as well as the analysis and control of process influences on the surface quality of optical components. The experiments were carried out on a 5-axis CNC machine. Rapid subsequent analysis of the topography resulting from grinding is achieved with the aid of white light interferometry. The aim of the investigations is to reduce the surface deviations (roughness, mid-spatials, waviness) influenced by process factors. It is shown that the vibration data measured during the grinding process correlate to a high degree with the recorded topography data.

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

The experimental setup shall compare face grinding with lateral grinding in a single processing step using fused silica and BK7 as materials. Resin and metal bonded tools are used in face and lateral grinding strategies. The paper presents the results in order to deepen the knowledge about those grinding technologies and to further improve the properties of fabricated components. Furthermore, the results confirm, that ultra-fine grinding is a technology, which can be used to process inorganic non-metallic materials with high quality surfaces with a low roughness and high flatness in a low processing time.

In the field of optical manufacturing, fused silica has a high and constantly growing application potential. Its material advantages, such as low thermal expansion and high thermal shock resistance, as well as its high transparency from the ultraviolet to the infrared spectral range, result in a large number of application fields. For example, manufacturing processes in semiconductor technology require high-quality quartz materials throughout the wafer handling process to avoid non-permissible contamination and to withstand the high process temperatures. Another example are monolithic components for fiber preform manufacturing, where internal contours with high aspect ratios (e.g. component length to component diameter) and high surface qualities are required to draw fiber types with special properties. The demands on the complexity and accuracy of these components are constantly increasing, which is accompanied by the need to analyse and optimize modern CNC manufacturing techniques more and more. In the following, investigations on the grinding of internal contours with a high aspect ratio are presented, in which the influence of an ultrasonic assistance as well as different machining strategies are considered.

Inorganic non-metallic materials are widely used in many application areas such as precision optics, semiconductor technology, high-temperature technology or medical technology. This increasingly requires the application of precise multi-axis CNC machine technology and poses great challenges for the machining processes, especially with regard to the economic production of high-quality surfaces. In the field of optics technology, high surface qualities in the nanometer range are often required. The production machines designed for this purpose must therefore guarantee a high degree of accuracy and be constant with respect to their environmental factors. An influence on the quality of the machining results that should not be underestimated is the vibrations occurring on the machine, which are caused on the one hand by the operating vibrations generated by the running spindle, and on the other hand by resonance frequencies. A side effect of these vibrations can also be damage to the workpiece or the tool. In order to detect these influences, a modal analysis and a measurement of the operating vibration mode are carried out on an ultrasonic-assisted CNC grinding machine using a three-dimensional laser Doppler vibrometer system provided by Polytec GmbH. In addition, corresponding measurements are carried out by means of a one-dimensional laser Doppler vibrometer on a 5-axis CNC universal milling machine in order to establish comparability between an ultrasound-assisted and a conventional processing machine.

Ultra-fine grinding is a technology, which can be used to process inorganic non-metallic materials. High quality surfaces with a low roughness, and high flatness are achievable in a low processing time. The experimental setup which is described shall compare face grinding with lateral grinding in a single processing step using various materials, bonds and processing parameters. The results are supposed to deepen the knowledge about this grinding technology to further improve the properties of fabricated components.

Many optical applications require splitting or deflection of light beams. This usually is achieved by usage of standard plane optical elements such as mirror systems or prismatic elements. However, these components are usually limited to one certain function and the manufacturing process for achieving precise functionality is very demanding. The presented research topic shows the development of new optical multifunctional components that introduce certain advantages compared to existing plane optical components. The basic roof-element configuration is based on glass cuboids joined together under a certain angle that can be fine adjusted during the manufacturing process. The components are therefore rather simply built and robust, and can fulfil different optical functions simultaneously by modifications of the glass cuboids. A process chain was developed for efficient and flexible manufacturing of such plane optical elements. Technical investigations were made on novel manufacturing processes such as ultrasonic assisted grinding and ultrafine grinding for fabrication of the cuboid parts, as well as diffusion joining being one possibility to create the basic roof-element shape.

The material fused silica, as well as other brittle-hard materials such as glass ceramics, have great potential for use in a wide range of applications due to their special material properties. The technical advantages of these materials require sophisticated processing technologies, including polishing steps, in order to be able to use these interesting materials advantageously. In addition, a current trend in modern optical manufacturing is the use of free-form surfaces and monolithic components that combine several optical and mechanical functions in one part. Novel or improved processes are needed in order to meet future requirements for resource-saving and effective production methods at the same time.

We present a feasibility study with several magnetic field configurations for creating spin-dependent forces that can split a low-energy ion beam by the Stern–Gerlach (SG) effect. To the best of our knowledge, coherent spin-splittings of charged particles have yet to be realised. Our proposal is based on ion source parameters taken from a recent experiment that demonstrated single-ion implantation from a high-brightness ion source combined with a radio-frequency Paul trap. The inhomogeneous magnetic fields can be created by permanently magnetised microstructures or from current-carrying wires with sizes in the micron range, such as those recently used in a successful implementation of the SG effect with neutral atoms. All relevant forces (Lorentz force and image charges) are taken into account, and measurable splittings are found by analytical and numerical calculations.

Minimizing the CEP jitter of isolated attosecond pulses (IAP) will be important for future applications. This jitter is experimentally and theoretically investigated and can be minimized when the driving pulse is near its Fourier limit but with slightly negative chirp. Thus, understanding and characterization of the CEP jitter of IAPs is a first step towards exact control of the electric field of IAP pulses.

We report on results on the preparation of thin (

We present a general analysis of the cooling produced by losses on condensates or quasi-condensates. We study how the occupations of the collective phonon modes evolve in time, assuming that the loss process is slow enough so that each mode adiabatically follows the decrease of the mean density. The theory is valid for any loss process whose rate is proportional to the $j$th power of the density, but otherwise spatially uniform. We cover both homogeneous gases and systems confined in a smooth potential. For a low-dimensional gas, we can take into account the modified equation of state due to the broadening of the cloud width along the tightly confined directions, which occurs for large interactions. We find that at large times, the temperature decreases proportionally to the energy scale $mc^2$, where $m$ is the mass of the particles and $c$ the sound velocity. We compute the asymptotic ratio of these two quantities for different limiting cases: a homogeneous gas in any dimension and a one-dimensional gas in a harmonic trap.

The electric-field noise above a layered structure composed of a planar metal electrode covered by a thin dielectric is evaluated and it is found that the dielectric film considerably increases the noise level, in proportion to its thickness. Importantly, even a thin (mono) layer of a low-loss dielectric can enhance the noise level by several orders of magnitude compared to the noise above a bare metal. Close to this layered surface, the power spectral density of the electric field varies with the inverse fourth power of the distance to the surface, rather than with the inverse square, as it would above a bare metal surface. Furthermore, compared to a clean metal, where the noise spectrum does not vary with frequency (in the radio-wave and microwave bands), the dielectric layer can generate electric-field noise which scales in inverse proportion to the frequency. For various realistic scenarios, the noise levels predicted from this model are comparable to those observed in trapped-ion experiments. Thus, these findings are of particular importance for the understanding and mitigation of unwanted heating and decoherence in miniaturized ion traps.

We investigate the role of interatomic interactions when a Bose gas, in a double-well potential with a finite tunneling probability (a ‘Bose–Josephson junction’), is exposed to external noise. We examine the rate of decoherence of a system initially in its ground state with equal probability amplitudes in both sites. The noise may induce two kinds of effects: firstly, random shifts in the relative phase or number difference between the two wells and secondly, loss of atoms from the trap. The effects of induced phase fluctuations are mitigated by atom–atom interactions and tunneling, such that the dephasing rate may be suppressed by half its single-atom value. Random fluctuations may also be induced in the population difference between the wells, in which case atom–atom interactions considerably enhance the decoherence rate. A similar scenario is predicted for the case of atom loss, even if the loss rates from the two sites are equal. We find that if the initial state is number-squeezed due to interactions, then the loss process induces population fluctuations that reduce the coherence across the junction. We examine the parameters relevant for these effects in a typical atom chip device, using a simple model of the trapping potential, experimental data, and the theory of magnetic field fluctuations near metallic conductors. These results provide a framework for mapping the dynamical range of barriers engineered for specific applications and set the stage for more complex atom circuits (‘atomtronics’).

We argue that the theories of Volokitin and Persson (2014 New J. Phys. http://dx.doi.org/10.1088/1367-2630/16/11/118001 16 http://dx.doi.org/10.1088/1367-2630/16/11/118001 ), Dedkov and Kyasov (2008 J. Phys.: Condens. Matter http://dx.doi.org/10.1088/0953-8984/20/35/354006 20 http://dx.doi.org/10.1088/0953-8984/20/35/354006 ), and Pieplow and Henkel (2013 New J. Phys. http://dx.doi.org/10.1088/1367-2630/15/2/023027 15 http://dx.doi.org/10.1088/1367-2630/15/2/023027 ) agree on the electromagnetic force on a small, polarizable particle that is moving parallel to a planar, macroscopic body, as far as the contribution of evanescent waves is concerned. The apparent differences are discussed in detail and explained by choices of units and integral transformations. We point out in particular the role of the Lorentz contraction in the procedure used by Volokitin and Persson, where a macroscopic body is ‘diluted’ to obtain the force on a small particle. Differences that appear in the contribution of propagating photons are briefly mentioned.

The electromagnetic force on a polarizable particle is calculated in a covariant framework. Local equilibrium temperatures for the electromagnetic field and the particle's dipole moment are assumed, using a relativistic formulation of the fluctuation–dissipation theorem. Two examples illustrate radiative friction forces: a particle moving through a homogeneous radiation background and above a planar interface. Previous results for arbitrary relative velocities are recovered in a compact way.