Imperfect refractive index matching in scanning laser optical tomography and a method for digital correction.

Significance: Scanning laser optical tomography (SLOT) is a volumetric multi-modal imaging technique that is comparable to optical projection tomography and computer tomography. Image quality is crucially dependent on matching the refractive indexes (RIs) of the sample and surrounding medium, but RI matching often requires some effort and is never perfect. Aim: Reducing the burden of RI matching between the immersion medium and sample in biomedical imaging is a challenging and interesting task. We aim at implementing a post processing strategy for correcting SLOT measurements that have errors caused by RI mismatch. Approach: To better understand the problems with poorly matched Ris, simulated SLOT measurements with imperfect RI matching of the sample and medium are performed and presented here. A method to correct distorted measurements was developed and is presented and evaluated. This method is then applied to a sample containing fluorescent polystyrene beads and a sample made of olydimethylsiloxane with embedded fluorescent nanoparticles. Results: From the simulations, it is evident that measurements with an RI mismatch larger than 0.02 and no correction yield considerably worse results compared to perfectly matched measurements. RI mismatches larger than 0.05 make it almost impossible to resolve finer details and structures. By contrast, the simulations imply that a measurement with an RI mismatch of up to 0.1 can still yield reasonable results if the presented correction method is applied. The experiments validate the simulated results for an RI mismatch of about 0.09. Conclusions: The method significantly improves the SLOT image quality for samples with imperfectly matched Ris. Although the absolutely best imaging quality will be achieved with perfect RI matching, these results pave the way for imaging in SLOT with RI mismatches while maintaining high image quality.

Development of a density-based topology optimization of homogenized lattice structures for individualized hip endoprostheses and validation using micro-FE.

Prosthetic implants, particularly hip endoprostheses, often lead to stress shielding because of a mismatch in compliance between the bone and the implant material, adversely affecting the implant's longevity and effectiveness. Therefore, this work aimed to demonstrate a computationally efficient method for density-based topology optimization of homogenized lattice structures in a patient-specific hip endoprosthesis. Thus, the root mean square error (RMSE) of the stress deviations between the physiological femur model and the optimized total hip arthroplasty (THA) model compared to an unoptimized-THA model could be reduced by 81 % and 66 % in Gruen zone (GZ) 6 and 7. However, the method relies on homogenized finite element (FE) models that only use a simplified representation of the microstructural geometry of the bone and implant. The topology-optimized hip endoprosthesis with graded lattice structures was synthesized using algorithmic design and analyzed in a virtual implanted state using micro-finite element (micro-FE) analysis to validate the optimization method. Homogenized FE and micro-FE models were compared based on averaged von Mises stresses in multiple regions of interest. A strong correlation (CCC > 0.97) was observed, indicating that optimizing homogenized lattice structures yields reliable outcomes. The graded implant was additively manufactured to ensure the topology-optimized result's feasibility.

Parametric multiphysics study of focus-variable silicone lenses.

By exploiting their inherent elasticity, focus-variable silicone lenses shift their focal length reversibly when deformed. Although biconcave and meniscus lenses contribute to optical systems just as well as biconvex lenses, studies primarily revolve around the latter. Thus, we aim to reveal the focal length shifting potential of all aforementioned lens types. Covering a wide parameter range of varying lens curvature radii, we present a coupled mechanical and optical simulation in which a lens deformation is applied. The results show significant differences in focal length shifting effectiveness for different lens types. Within the domains of specific lens types, trends in this effectiveness emerge for different combinations of curvature radii. Matching these radii when incorporating adaptive silicone lenses in optical systems may guide optics engineers toward more effective system designs through this study.

Additive manufacturing of multi-material parts - Design guidelines for manufacturing of 316L/CuCrZr in laser powder bed fusion.

Additive manufacturing (AM) can be used to produce multi-material parts in which the material can be varied voxel-wise in all three spatial directions. This means that the paradigm of the homogeneous material can be abandoned and local effects such as heat conduction or damping can be selectively adjusted in the part. Recently, continuous development of machine technology has allowed the production of multi-metal materials in laser powder bed fusion (PBF-LB/MM). Compared to other additive manufacturing processes for multi-material production, this allows greater design freedom and detail accuracy to be realized. However, due to the novel character of multi-material manufacturing in PBF-LB, the process knowledge for successful and reproducible fabrication is currently lacking. This paper focuses on establishing design guidelines for manufacturing the material pairing of stainless steel 316L (1.4404) and copper alloy CuCrZr (CW106C). The article is accompanied by the development of a specific process chain. As a result of this work, design guidelines for multi-material parts are available for the first time, in regard to arrangement, size, overhangs, economy, powder quality and laser scanning.

Optimizing LERP systems: opto-thermal steady-state simulation analysis and experimental validation.

Laser-excited remote phosphor (LERP) systems are the next step in solid-state lighting technology. However, the thermal stability of phosphors has long been a major concern in the reliable operation of these systems. As a result, a simulation strategy is presented here that couples the optical and thermal effects, while the phosphor properties are modeled to temperature. A simulation framework is developed in which the optical and thermal models are defined in Python using appropriate interfaces to commercial software: the ray tracing software Zemax OpticStudio for the optical analysis and the finite element method (FEM) software ANSYS Mechanical for the thermal analysis. Specifically, the steady-state opto-thermal analysis model is introduced and experimentally validated in this study based on Ce:YAG single-crystals with polished and ground surfaces. The reported experimental and simulated peak temperatures are in good agreement for both the polished/ground phosphors in the transmissive and reflective setups. A simulation study is included to demonstrate the simulation's capabilities for optimizing LERP systems.

Requirements for Automotive LiDAR Systems.

Light detection and ranging (LiDAR) are fundamental sensors that help driving tasks for autonomous driving at various levels. Commercially available systems come in different specialized design schemes and involve plenty of specifications. In the literature, there are insufficient representations of the technical requirements for LiDAR systems in the automotive context, such as range, detection quality, resolving power, field of view, and eye safety. For this reason, the requirements above require to be derived based on ADAS functions. The requirements for various key LiDAR metrics, including detection range, field of view, angular resolution, and laser safety, are analyzed in this paper. LiDAR systems are available with various radiation patterns that significantly impact on detection range. Therefore, the detection range under various radiation patterns is firstly investigated in this paper. Based on ADAS functions, the required detection range and field of view for LiDAR systems are examined, taking into account various travel speeds to avoid collision and the coverage of the entire lane width. Furthermore, the angular resolution limits are obtained utilizing the KITTI dataset and exemplary 3D detection algorithms. Finally, the maximum detection ranges for the different radiation patterns are compared under the consideration of derived requirements and laser safety.

CO2-laser-ablation-assisted fabrication of signal-pump combiners with chirally coupled core fibers for co- and counter-pumped all-fiber amplifiers.

We report on the development of a side-fused signal-pump combiner with an integrated feed-through 34/250-µm chirally coupled core fiber. The manufacturing process involves a novel rotationally symmetrical cladding restructuring using a CO2-laser beam. The signal-pump combiner exhibits the pump-to-signal fiber coupling efficiency of 90%, signal-to-pump isolation of 30 dB, and is high-power tested at a pump input power of >500 W. Additionally, a signal feed-through loss of 0.23 dB is measured and the S2-method is used to confirm non-degradation of the spatial modes. The side-fused combiner technique has the advantage of an uninterrupted signal core and can be used in co- and counter-pumped configurations.

Impact of industrial environments on visible light communication.

Visible-light communication is a promising technology for industrial environments. However, a variety of physical effects may influence the communication quality in this potentially harsh environment: Dust and other particles lead to increased attenuation. Artificial light sources and industrial processes, such as grinding and welding, cause optical cross-talk. A multitude of reflective surfaces can lead to fading due to multi-path propagation. These three aspects are experimentally investigated in exemplary manufacturing processes at five different production sites in order to estimate the relative importance and their specific impact on VLC transmission in industrial areas. Spectral measurements demonstrate the presence of interfering light sources, which occupy broad parts of the visible spectrum. They give rise to flickering noise, which comprises a set of frequencies in the electrical domain. The impact of these effects on the communication is analysed with reference to the maximum achievable channel capacity and data rate approximation based on on-off keying is deduced. It is found that cross-talk by environmental and artificial light sources is one of the strongest effects, which influences the optical, but also the electrical spectrum. It is also observed that industrial areas differ strongly and must be categorised according to the manufacturing processes, which can induce quite a variation of dust and attenuation accordingly.

Polymer Optical Waveguide Sensor Based on Fe-Amino-Triazole Complex Molecular Switches.

We report on a polymer-waveguide-based temperature sensing system relying on switchable molecular complexes. The polymer waveguide cladding is fabricated using a maskless lithographic optical system and replicated onto polymer material (i.e., PMMA) using a hot embossing device. An iron-amino-triazole molecular complex material (i.e., [Fe(Htrz)2.85(NH2-trz)0.15](ClO4)2) is used to sense changes in ambient temperature. For this purpose, the core of the waveguide is filled with a mixture of core material (NOA68), and the molecular complex using doctor blading and UV curing is applied for solidification. The absorption spectrum of the molecular complex in the UV/VIS light range features two prominent absorption bands in the low-spin state. As temperature approaches room temperature, a spin-crossover transition occurs, and the molecular complex changes its color (i.e. spectral properties) from violet-pink to white. The measurement of the optical power transmitted through the waveguide as a function of temperature exhibits a memory effect with a hysteresis width of approx. 12 °C and sensitivity of 0.08 mW/°C. This enables optical rather than electronic temperature detection in environments where electromagnetic interference might influence the measurements.

Polymer-based diffractive optical elements for rear end automotive applications: design and fabrication process.

Advances in illumination technology in the automotive industry are heading toward the use of coherent sources for adaptable and high-resolution head lamps as well as interior and rear-end lights. We present a cost-effective method to fabricate and design laser-based lighting systems for the rear end in automobiles and other vehicles. The design relies on using binary gratings to generate a desired intensity distribution. For cost-effective fabrication, an optical maskless UV lithography system that employs a spatial light modulator (SLM) for projection of the desired structure onto photoresist is introduced. To replicate the structures onto polymers like poly(methyl methacrylate) (PMMA), we use polydimethylsiloxane soft stamps and a hot embossing system. The experimental results show that the proposed design and fabrication process is promising for high-resolution rear-end lights that might be employed to project symbols or information to guide road users in future.