The feasibility of using beam shaped short femtosecond pulses in combination with a nonlinear frequency conversion process to create any arbitrary beam shape in the ultraviolet spectrum is shown. Broadband femtosecond pulses (800 nm centre, 30 nm Bandwidth FWHM, 50 fs) are shaped via a spatial light modulator (SLM) and converted to 400 nm in a subsequent second harmonic process to 400 nm in a collinear setup while conserving the beam shape information by using orthogonal polarisation states to avoid beam shape degradation. Additionally, it is shown, that the holograms exhibit blurred edges due to chromatic dispersion stemming from the bandwidth of the utilized fs pulses and the conversion efficiency is linked to the angular spectrum created at the SLM.

Solidification cracking in laser beam welding (LBW) is governed by local thermal conditions at the weld-pool boundary, yet the sub-micron microstructural response across the full mushy zone remains poorly understood. This study employs an automated phase-field (PF) simulation workflow, integrated within the Kadi4Mat research data management platform, to conduct a systematic, FAIR-compliant parametric study of dendritic solidification in the quaternary EN 1.4301 (Fe–Cr–Ni–C) alloy. Thermal conditions—thermal gradient (G), solidification velocity (Vs), and grain misorientation angle (θR)—are extracted from a thermocouple-validated ANSYS Fluent weld-pool model and used as inputs to 2D and 3D PACE3D phase-field simulations spanning G from 100 to 900 K/mm, Vs from 5 to 40 mm/s, and θR from 0∘ to 45∘. Key findings demonstrate that θR is a critical parameter—alongside G and Vs—governing the cellular-to-dendritic morphological transition, secondary dendrite arm formation, and the topology of inter-dendritic liquid (continuous films versus isolated pockets), each carrying distinct solidification cracking risk pathways. The Kadi4Mat workflow reduces manual pre-processing effort substantially while ensuring data reproducibility and reuse. Quantitative validation against electron probe micro-analysis confirms primary dendrite arm spacing predictions within 12% at the upper weld surface and within 4% at the mid-section.

Shaping the spatial intensity profile of the process laser beam is a promising approach for improving part and surface quality in laser powder bed fusion. However, practical implementation is limited by logistical or economic constraints, since the process beam shape needs to be adapted depending on the material and print process conditions, often involving specialized laser sources or complex optical setups. Here, a single refractive focal beam shaping optic is employed to realize laser beam intensity variations of Gaussian, flat-top (tophat) and annular (ring) beams by controlled defocusing. Additionally, a conduction-mode thermal model using measured beam profiles and temperature-dependent properties is implemented. The model correlates well with published single-track melt pool dimensions for Gaussian and ring beams and predicts lack-of-fusion defects. The observations indicate that tophat and shallow ring beam profiles lead to a smaller spread of part density values in SS 316L across low to moderate energy densities, compared to other beam profiles explored in the study. Topographical characterization of the top surfaces indicates that tophat beams exhibit superior surface quality (lower roughness).

Directed Energy Deposition of metals with the laser beam (DED-LB/M) enables near-net-shape fabrication and thereby reduces post-processing steps. The capability to process Ni-based superalloys such as Haynes 282 and Waspalloy makes the technique particularly attractive for aerospace and gas turbine applications. Nevertheless, it is desirable to further improve part properties such as surface roughness, microstructure and associated hardness in order to minimize post-processing. This study investigates the influence of three coherently combined beam profiles (ring, spiral and top-hat) on surface roughness, microstructure, and microhardness. It could be seen that the influence of the used beam profiles on the surface roughness of the side and top surfaces is negligible. Furthermore, the hardness of the samples was more influenced by the processing and boundary conditions than the beam profile. Despite this, a minor influence of the beam profile on the grain structure was observed.

Premixed hydrogen combustion is increasingly important as a technology for decarbonizing high-temperature industrial processes. The design flexibility enabled by additive manufacturing provides new opportunities to realize complex burner geometries that are difficult or impossible to produce with conventional methods. By coupling it with geometry optimization based on numerical simulations, the development of burners with increased stability, extended fuel and power flexibility, and reduced pollutant emissions becomes possible. In this study, three different modular burner nozzle designs are systematically compared with respect to these optimization targets using a newly developed diagnostic framework. Distinct differences between the nozzle configurations are identified in terms of their operational range, as characterized by flame stability maps. Simultaneous OH and CH2O planar laser-induced fluorescence (PLIF), in combination with OH* chemiluminescence measurements, are employed to analyze the main location of heat release. Complementary infrared measurements of both the nozzle and the flame temperature (at a fixed location in the flames) reveal strong correlations between flame stability characteristics, heat release location, and a possible feedback into the nozzle material. We conclude that these mainly result from the difference between the local mixture distribution of the nozzles. Based on this experimental framework, the characterization and evaluation of optimized design geometries become possible.

ABSTRACT The penetration depth of light within biological tissue is typically restricted by the optical diffusion limit to one transport mean free path primarily due to the multiple scattering. While whispering gallery mode (WGM) microlasers are promising internal light sources in tissue, their application has been limited to depths of a few hundred , likely due to the low signal intensity of small gain volume. Here, we demonstrate robust WGM lasing at depths significantly beyond the diffusion limit using a functionalized commercial nylon fiber with a diameter of 260 . The fiber's high refractive index () and mechanical flexibility enable efficient optical confinement and tissue integration. Benefiting from an enlarged gain volume, high‐quality WGM laser emission with discrete periodic resonances was maintained at depths of 5 mm in scattering phantoms (up to 53) and 3 mm beneath porcine skin. This work establishes the dye‐functionalized nylon fiber as a scalable architecture for high‐quality light generation deep in optically challenging biological environments. Integrating such lasing capabilities into existing medical filaments such as sutures in the future may pave the way toward long‐term in situ deep‐tissue therapeutics and diagnostics.

Thin film contamination on critical surfaces is a significant cause of failure in different industries, including semiconductor, optical and medical manufacturing. Especially surfactants can alter surface properties that subsequent production steps and product quality are impacted. The contactless, non-destructive and fast detection of those trace organic residues remains a substantial metrological frontier. In this paper we establish epi-CARS Microscopy as a quantitative tool for mapping those contaminations. Using CARS in reflection on opaque surfaces poses certain obstacles, like non-resonant substrate background concealing the contaminants chemical signal and non-linear relationship between signal intensity and contaminant thickness. We describe the coherent interplay between the CARS signal arising from contaminant and substrate. By analyzing that signal, we decouple vibrational response from optical artifacts, thereby quantifying spatially resolved contaminant thickness. We validate this by analyzing silicon wafer samples contaminated with dimethylpolysiloxane in combination with AFM thickness verification. The epi-CARS detection limit for filmic contamination is determined, consequently more time-consuming and extensive techniques can be substituted. The ability to create quantitative maps of thin silicone films within seconds, achieving nanometer thickness sensitivity, is demonstrated. Quantitative epi-CARS is established as a fast, reliable, high-resolution and large-area analytical tool for surface cleanliness validation and contamination identification.

Electrified powertrains demand robust and precise copper joining technologies. This study investigates the influence of spatial beam oscillation trajectory and frequency on weld penetration depth, seam width, and surface roughness in high-power blue diode laser welding (445 nm, PL,max = 4 kW) of Cu-ETP. Circular, infinity-shaped, and sine oscillation trajectories were examined across a frequency range of 0 to 1000 s⁻¹ at constant welding velocity and nominal oscillation amplitude. All parameter combinations yielded pore-free and spatter-free weld seams, confirming stable conduction mode welding throughout. Penetration depth is most effectively recovered at high frequencies by the infinity-shaped trajectory, which transitions to a stationary melt pool regime above a critical frequency threshold of fo = 350 s⁻¹, enabling continuous energy coupling into the depth direction. Sine oscillation yields the lowest surface roughness, operating in a weaving melt pool regime with intermittent resolidification between successive passes that dampens surface disturbances and promotes smooth resolidification. Weld width scales geometry-independently with the effective lateral amplitude and decreases with scanner-induced roll-off for all trajectories. The dimensionless path length factor ψ and the trajectory-weighted area energy density Êeff together provide a geometry-independent framework that captures the observed trade-offs between penetration depth, seam width, and surface roughness across all trajectories examined.

Spatial laser beam shaping is investigated to assess its influence on surface roughness in laser powder bed fusion (PBF-LB) of 316L stainless steel. A high-fidelity CFD model developed in FLOW-3D simulates Gaussian (GBP) and Ring-spot (RSBP) beam profiles, resolving laser absorption, free-surface evolution, recoil pressure, and Marangoni flow. Analytical heat sources are calibrated to measured beam profiles, and the predictions are validated against single-track melt-pool cross-sections (RMSE ≈ 6.5%) and single-layer surface topography. Under baseline conditions, the RSBP produces a wider and shallower melt pool that suppresses tail-end humping and reduces surface roughness, with simulated decreases of ~10.2% in Sa, ~36.2% in Sq, and ~44.9% in Sz relative to the GBP. Texture becomes more isotropic with the RSBP, as indicated by the Str index increasing from 0.0714 to 0.1429. Although open pores appear on RSBP surfaces at baseline power, increasing the laser power to 300 W eliminates these defects while maintaining superior surface quality compared to the GBP. Abbott–Firestone analysis shows a lower Smr1 for the RSBP, indicating fewer high peaks and a narrower functional core height. The simulations reproduce these experimental trends, establishing a predictive link between beam profile, melt-pool morphology, and resulting surface roughness and texture.

Parameter studies in PBF-LB/M are common but are difficult to compare due to variations in material or machine conditions. Volume energy density (VED) is frequently used to condense process parameters into a single, simplified metric. However, VED is not suitable for scaling between machines and materials. Using a low alloy steel as an example, a full-factorial parameter study, including beam shaping, is presented and evaluated in terms of density and surface roughness using VED and two existing dimensionless approaches based on the Peclet number. The influence of varying layer height is analyzed and discussed. Both dimensionless approaches enable process parameter scaling within the discussed constraints. The process stabilization at the process window onset through beam shaping is demonstrated while the required energy input for comparable density and roughness is reduced. Surface roughness proves as a reliable indicator of process stability at the process window onset, particularly for shaped beam configurations.

Coherent Beam Combining (CBC) enables near-unlimited variation of spatial laser intensity distributions, offering a novel approach to beam shaping in laser-based directed energy deposition of metals (DED-LB/M). To assess the influence of beam shape on the resulting microstructure and mechanical properties, super duplex steel thin-walled multilayer specimens were fabricated using four distinct beam profiles and comprehensively characterized. The spatial intensity distribution was found to directly govern solidification conditions, grain morphology, crystallographic texture and austenite precipitation behavior. A direct influence of the beam profiles on the geometric key values and specimen quality has been observed as well. Notably, a beam profile with laterally distributed intensity peaks promoted stronger crystallographic texture through variations in the spatially distributed G/R criterion. The results demonstrate that spatial intensity distribution represents an effective parameter for targeted microstructure and property engineering in DED-LB/M.

Laser-induced Breakdown Spectroscopy (LIBS) is a rapid, non-invasive analytical technique which makes it particularly well-suited to biomedical screening applications. For biomedical screening applications usually blood samples are used. Unlike blood samples, which exhibit short-term fluctuations and require an invasive puncture to collect, fingernails allow long-term health assessment over several months due to their slow growth. In this study, 43 fingernail samples from volunteers were analyzed to determine sex, age and lifestyle factors. LIBS revealed differences in elemental composition: women exhibited higher Ca/K intensity ratios, whereas men showed higher Mg/K and H/K levels. Age significantly influenced the concentrations of the elements C, Fe, H, Mg, N, Na, O, and S. Non-drinkers displayed higher Ca/K, Fe/K and Mg/K levels. Dietary factors showed significant influence for Ca, N, Na, O and S on elemental concentrations. These findings were statistically validated using mixed models. Regardless of sex, age, or lifestyle, LIBS analysis identified three distinct spectral groups with characteristic patterns across all measurements, suggesting previously unrecognized physiological relationships. These results demonstrate the potential of LIBS for the non-invasive, long-term monitoring of elemental status and lifestyle parameters via fingernail analysis. This could create new opportunities for screening human lifestyles or clinical disease indicators.

This study investigates powder stream characteristics, including powder focus and particle velocity, in laser-directed energy deposition of polymers (DED-LB/P) using high-speed imaging. PEEK and PA12, two commonly used thermoplastic powders, differ in particle morphology, flowability and thermal properties. Systematic analysis reveals strong material dependent behavior, with PEEK exhibiting a narrower focus and higher velocities than PA12 under identical conditions. Carrier gas flow significantly affects particle velocity, while shielding gas has negligible impact. Powder flowability, particle size distribution, and the loading ratio are identified as key factors influencing powder stream characteristics, providing essential insights for optimizing polymer DED processes.

Additive manufacturing (AM) of high-speed steel (HSS) is of great interest for the manufacture of optimized forming and cutting tools. This study aims to systematically develop the sinter-based Cold Metal Fusion process for M2 steel and enable manufacture of complex shaped part designs. Green parts were printed with surface roughness, R-a, of 21 mu m and density of 5.40 g/cm(3). A sintering temperature of 1248 degrees C yielded a sintered density of >99% theoretical density and significantly decreased surface roughness to 8-10 mu m. The microstructure consisted of martensite, and of grain boundary and finer intragranular MC and M6C carbides. As-sintered Vickers hardness was 576 + 10 HV5 and increased to 933+ 27 HV5 upon oil quenching. Compression tests after air quenching revealed superior compressive strength of >3360 MPa compared to the as-sintered and oil cooled HSS. The fracture mode changed from ductile transgranular fracture for the as-sintered material to brittle intergranular upon oil cooling. As-sintered tensile specimens showed low strength of 681 + 43 MPa and brittle intergranular fracture as opposed to the as-sintered compression specimens. Finally, the manufacturing capability for an injection molding tool insert was proven, as no defects were identified. This novel process will allow for the manufacture of complex high-performance parts with improved durability and efficiency.

Unlike conventional Laser-induced Breakdown Spectroscopy (LIBS), calibration-free LIBS (CF-LIBS) enables quantitative elemental analysis without the need for empirical calibration curves or reference standards. When the conditions of stoichiometric ablation, optically thin plasma, and local thermodynamic equilibrium are met, elemental concentrations can be calculated directly from the emission spectrum. However, accurate quantification is often difficult due to peak overlaps, which can be caused by limitations in spectral resolution, for example. This requires careful peak selection to prevent systematic errors in automated routines. This study addresses these challenges by developing an automated algorithm that identifies the spectral lines of a 10-cent euro coin by cross-referencing them with the NIST database. The algorithm evaluates peak morphology to determine the suitability of each transition for concentration analysis. The results show that the algorithm correctly identifies over 80% of the target peaks, yielding a calculated plasma temperature of 9 868 K. The determined elemental concentrations, 90% Cu, 6% Al, 3% Zn, and 1% Sn, demonstrate high precision, agreeing closely with existing literature data for these coins. This automated methodology provides an alternative approach to calculating concentrations using CF-LIBS.

Calibration-free laser-induced breakdown spectroscopy (CF-LIBS) has the advantage of eliminating the need for complex sample preparation. This study investigates the impact of various preparation techniques on porcine tissue. These methods include embedding the tissue in PBS or deionised water, and analysing untreated tissue or tissue that has been cut using liquid nitrogen. The results demonstrate that embedding samples does result in changes to the LIBS spectra. Minor deviations in the magnesium and sodium intensity ratios were observed in the skin. However, it should be noted that embedded samples may exhibit altered elemental signatures due to ionic exchange with the immersion medium, despite facilitating sample handling. It is important to note that the immediate measurement of untreated samples is critical, as post-mortem changes can lead to shifts in elemental concentrations. These findings show that CF-LIBS can be reliably performed on untreated biological samples, thus supporting its use in vivo diagnostics.

Austenitic stainless steel of type 316L is widely used in industrial hydrogen applications due to its advantageous material properties. The interaction between these material characteristics and hydrogen has been intensively studied for decades. Alongside, additive manufacturing enables new degrees of design freedom as well as the tailored control of material properties. In this work, laser-based powder bed fusion of metals (PBF-LB/M) is used in combination with several post-processes and heat treatments to manufacture 316L specimens with different application related surface and microstructures. After surface analysis, gaseous hydrogen charging in an autoclave at 300 °C and 100 MPa was conducted. Subsequently, the hydrogen uptake was measured via inert gas fusion. The investigation show that the microstructure has a more significant influence on hydrogen uptake than the surface quality. By optimizing the material properties of additively manufactured 316L through beam shaping and heat treatment, the hydrogen uptake was significantly reduced compared to conventionally cold-drawn 316L.

We present a method for overcoming the wavelength limitation of LCoS-SLM by using Second Hamonic Generation while preserving the beam shape. This was achieved by placing a Type-1 Phase-matched BBO-crystal in the Fourier-plane after the SLM. This method is able to frequency convert the hologram while preserving fine details and without being limited by the angular acceptance of the crystal. Additionally, by removing the necessity of having to work on-axis (like with previously shown Type-2 PM methods), the 0-order beam can be removed. We also found that the quality of the frequency converted hologram degrades, if the length of the crystal is longer than the hologram’s depth of focus due to interangular mixing.

Almost all industries depend on reliable adhesive bonds. Adhesive bonding is a “special process”, where non-destructive in-line inspections of the sample are not practicable. To ensure reliability, profound knowledge of the mechanisms of the adhesion and a proper understanding of the adhesive process is crucial. In this paper the impact of different thin silicone films and laser cleaning processes on the bond quality is assessed. Therefore, aluminum samples are contaminated with various thin silicone films and the laser cleaning process is applied. Afterwards the adhesive is dispensed, cured and the shear strength is measured. The results are interpreted based on five hypotheses that set the laser effect on the morphology change in relation to the laser cleaning effect. The transition zone between adhesive and samples is investigated using cross sections and the non-destructive imaging technique 3D-X-ray microscopy (XRM) scans. Furthermore, the surface free energy (SFE) and the surface roughness of the samples are measured and correlated with the shear strength. Our data show that the quality of adhesive bonding can be significantly improved through the interplay between various surface parameters and treatments.