Yttrium aluminium garnet (Y₃Al₅O₁₂–YAG) has been used in the industry for over 60 years now and lots of new ways for it’s synthesis have been discovered. However, since YAG is an inorganic material - it’s hard to make in a specific shape and size. This hinders it from being further applied in solid-state lasers (as microlasers), in light emitting diode’s (LED’s) (as making microLED’s would be more beneficial) and as light emitting material (phosphor). As currently YAG isn’t being structured on a commercial scale—this article showcases that it can be done with minimal effort and time. In this research, YAG precursors were synthesized, mixed with prepolymer and calcinated to obtain pure YAG. This work aims to show that it’s possible and also relatively easy to synthesize pre-structured YAG, describes it’s properties and also the characteristics of it’s lanthanide-doped versions.

STED-inspired sub-diffractional nanolithography was so far restricted to free radical polymerization, predominantly of (meth)acrylates. We now expand the STED-inspired toolkit to cationic and oxidative polymerization, comprising the technologically important classes of epoxides and π-conjugated polymers. In both cases, we achieved structure sizes below 100 nm using transient state absorption depletion (TAD) in systems comprising onium salts as initiators and photosensitizers that can be depleted by transient state absorption.

High-intensity and low-divergence laser beams can cause damage to the human eye, sensors, and photoreceptors. In harsh environments, optical sensors can be damaged by pulsed laser radiation if exposed beyond their capacity. To protect against such threats, passive optical limiting devices are used. These devices are self-activated systems with a low activation threshold, neutral color, and low response time. Methacrylate-based thermosets were synthesized via radical polymerization using a reactive oligomer and a monomer. Two processes were investigated in this study: thermal polymerization, which is solvent-free, allows to collect directly the sample and can take several hours, and 3D printing, which uses photopolymerization to produce samples. This is an innovative method that allows for the production of multiple samples in under 10 minutes. Furthermore, a non-linear dye has been incorporated into the methacrylate matrix. In this study, optical filters with a methacrylate matrix and a 0.01 wt% loading dye are prepared by bulk polymerization and photopolymerization processes. The samples are then characterized to demonstrate the same chemical composition and thermal behavior. Finally, the optical limiting properties of the thermoset polymers at a wavelength of 1064 nm are investigated. The two processes are compared to determine their relevance.

Grayscale laser lithography is capable of producing continuous-relief (2.5D) structures down to the micro- and nanoscale for applications such as micro-optics, micro-electromechanical systems and functional surfaces. The present work evaluates build accuracy by employing benchmark artefacts having an active area of up to 1 mm × 1 mm and a structure depth of up to 50 μm with a resolution of 1 μm as models for the production of 2.5D structures with a wide range of representative features in terms of elevation, slope, curvature, aspect ratio and area density. The topography of manufactured samples is determined via laser scanning confocal microscopy and 3D optical microscopy based on white light interferometry, with alignment algorithms developed within MATLAB employed to evaluate local build error over the entire surface. Further to the incident laser energy density within each region, the applied energy in adjacent regions is found to influence build accuracy due to the laser intensity distribution, light scattering and photochemical reaction effects, with the area density and aspect ratio of model features found to be of strong influence on outcomes. The results imply that greater build accuracy can be achieved by basing process parameters on not only the local model height but also that within adjacent regions. The present work was performed within the Horizon Europe project “Automated Maskless Laser Lithography Platform for First Time Right Mixed Scale Patterning” (OPTIMAL, Grant Agreement No. 101057029), with the aim of facilitating automated approaches for error correction and accuracy optimization.

We present the development and evaluation of metalenses fabricated with the two-photon polymerization-based 3D nanoprinting technology. In our design, we investigated a periodic lattice of multilevel nanopillars, based on the natural ellipsoidal shape of the 3D voxel in the fabrication process. By creating nanopillars with various heights, we can tune the effective refractive index of the metasurface in order to modulate the phase profile of an incoming light beam. We therefore push the fast and flexible two-photon polymerization technique to its limits in terms of dimensions in view of creating high performance metalenses. To demonstrate the optical performance of these metalenses, we also created their refractive and diffractive counterparts with the same fabrication technology to allow for a direct performance comparison. Moreover, we show that these metalenses can be fabricated on the tip of standard telecom single-mode optical fibers for the effective collimation of their output light beam.

The ability to manufacture complex 3D-objects directly from its CAD model is the important reason why additive manufacturing is being widely used to fabricate cost-efficient prototypes and preferred over conventional manufacturing methods. Moreover, it portrays as a bridging technology to connect different scientific and industrial fields, e.g. Engineering, Medicine, etc. Consequently, additive manufacturing finds its applications in the production of patient-specific orthoses. This paper discusses the development of a pressure sensor based on an optical waveguide principle manufactured using stereolithography apparatus process to embed into a below-knee orthosis. For Orthopedic patients, the below-knee orthosis must be adjusted to the lower leg at regular intervals due to anthropometric changes in patient’s body to achieve proper mobility and correct load. Currently, this alteration relies on the patient’s estimation of support load which is only sub-optimal. Hence, the concept of developing an intelligent orthosis with a novel embedded optical system to monitor the exact support load at the neuralgic is proposed.

Additive manufacturing is increasingly used for optical applications, especially for the production of the optical elements. However, larger elements usually require further post-processing steps of the optical surfaces and are not printable as monolithic multi-element systems. Nevertheless, optical systems can still benefit significantly by utilising the design freedom for the mounting structures. We designed a fully monolithic and additively manufactured mounting structure that is robust against mechanical and thermal influences from the environment and passively compensates their effects. We present our design approach and prove its feasibility by stressing an imaging lens and evaluating its optical performance.

Multi-photon polymerization is widely recognised as a promising approach for the fabrication of fully 3D micro or nano-metric structures. The ability to write such structures at high plot rates would open new frontiers in many fields such as health, optical micro-devices, security holograms etc. Parallelization of the fabrication process increases fabrication speed. In a first parallelization approach we use a short pulsed laser (picoseconds or femtoseconds) with a diffractive optical element which allows simultaneous fabrication with hundreds write spots, decreasing the overall fabrication time. In a second approach, a 1920 x 1080 pixel spatial light modulator is imaged into an ultra-sensitive resist using continuous wave laser. However, massive parallelization can lead to unwanted fabrication artefacts. Light field overlapping in out-of-focus planes and proximity effects are currently major issues limiting the performance of parallel micro fabrication processes due to the undesired polymerisation that results. We will present our latest photo-chemical process digital simulation results and show how they are enabling us to develop and apply precompensation techniques to the plot data to fabricate structures with a smaller Z-extent and/or circumvent proximity effects.

The polyethylene oxide (PEO)-based polymer electrolytes containing lithium salts pave the way for the development of safe lithium batteries with high energy storage capacity. Enabled by the flexibly vibrating polymer matrix, the Li-ion transport occurs via hopping along and between the polymer chains. Here, terahertz (THz) time-domain spectroscopy over a frequency range extending from 0.1 THz to 7 THz is applied to investigate the conduction properties of PEO-based electrolytes with lithium salts, and to elucidate the associated dependence of the THz conductivity on the content of the added lithium salt and the electrolyte temperature. It is remarkably found that the higher the observed THz vibrational activity of the electrolyte, the higher its technologically relevant ionic conductivity.

We study the formation of caustic surfaces produced by convex conic lenses, considering a linear set of point sources displayed on a plane, this linear array is placed at arbitrary position along the optical axis. The caustic surface can be defined as the envelope for either reflected or refracted rays propagating through an optical system. Implementing an exact ray trace, we have obtained an analytic equation that describes a parametric family of refracted rays propagating through a convex conic lens and by computing its envelope, we provide an exact equation for the caustic surface as a function of all the parameters involved in the process of refraction. Considering the geometric center of a conic surface, we have located the parabasal image for each point source produced by refraction, and by extending this concept for a set of point sources placed along a linear array, we obtain the image surface which is the locus where the succession of paraxial images are located. Finally, using a commercial 3D printer, we have fabricated a convex conic lens along with its image curved surface to implement a preliminary test to study the image formation for extended objects, with potential applications in uniform illumination systems.

Laser Additive Manufacturing (LAM) offers a versatile approach to fabricate composite materials, including heterogeneous and transition materials, characterized by exceptional mechanical properties. In this study, TiN/Ti6Al4V sandwich structural materials were prepared by the Selective Laser Melting (SLM) and Laser Directed Energy Deposition (LDED) processes, each in distinct environments featuring varying nitrogen-to-argon ratios. We conducted a comprehensive investigation, comparing the elemental diffusion, in-situ synthesis, microstructural characteristics, and mechanical properties of TiN/Ti6Al4V sandwich structural materials produced via these two processes. In both SLM and LDED processes, the in-situ synthesis of TiN from titanium and nitrogen atoms yielded robust metallurgical bonds with the Ti6Al4V matrix. The superior performance of TiN/Ti6Al4V sandwich structural materials achieved through LAM results from their laminar structure and the reinforcing effect of internal ceramic particles. Leveraging the combination of soft and hard layers within the sandwich structure, the tensile strength significantly surpasses that of homogeneous materials. Specifically, the sandwich structure materials synthesized through SLM and LDED attained impressive tensile strengths of 1303.1 MPa and 1155.1 MPa, respectively, alongside plastic deformations of 8.9% and 3.7%. This study highlights the potential of employing LAM in conjunction with controlled reactive atmospheres to fabricate new periodic heterogeneous materials in-situ, characterized by outstanding mechanical properties.

It is presently challenging for selective laser melting (SLM) additive manufacturing technique to fabricate metal parts with wall thickness below 100 μm. This work investigated the critical conditions of the extremely thin wall thickness of tungsten grids fabricated by SLM. Specifically, the effect of low energy density on the printability of tungsten single tracks and grids via SLM was studied. A thermo-fluid flow model of the molten pool created in the SLM process was developed based on a computational fluid dynamics approach to illustrate the single-track morphology variation corresponding to printability. The findings demonstrate that at low energy densities, the molten track exhibits four different morphologies: balling, discontinuity and winding, discontinuity but straightness, as well as continuity and straightness. The simulation model, reliably validated by these results, effectively reveals the correlation between printability and the extent of melting in the powder bed. The energy density impacts the heat transfer mechanism and recoil pressure magnitude within the molten pool, thereby determining its flowability to fill voids in the powder bed. Based on these findings, SLM process parameters were adjusted to achieve an ultra-thin wall thickness of the printed anti-scatter tungsten grid reaching 92 μm. This work not only provides theoretical insights but also presents a viable methodology for determining minimum energy density threshold and wall thickness required for SLM fabrication of ultra-thin-wall structural components.

In recent years, optical communication technologies receive more and more attention. Data sizes are growing consistently and fast. Therefore, increasing the data rates in optical telecommunication networks is of utmost importance.

By simultaneously transmitting multiple channels over a single fiber optic cable, data rates can be increased significantly. Wavelength Division Multiplexing (WDM) implements this idea technically. Considering optical long-distance communication via glass fiber, the concept of WDM is well established and components are commercially available. On the other side, optical short-distance communication via optical polymer fibers (POF) lack the availability of WDM, which leads to a much smaller available bandwidth.

Within the “Opti-AWG 3D” project at Jade University of Applied Sciences in Wilhelmshaven, a WDM for POF is being developed. The design will be based on an Arrayed Waveguide Grating (AWG). Due to different properties of polymers, a complete redesign of glass-based WDM is necessary. To realize this project, ray-optical as well as wave-optical simulations are conducted. Different approaches for the calculation and simulation of multimode AWG are investigated.