Search Results (761)

The research methodology involved creating a 3D sample model that featured both flat and cylindrical surfaces inclined at angles ranging from 0° to 90° relative to the XY plane. The study investigated the surface topography of additively manufactured samples produced using various technologies, including Fused Filament Fabrication (FFF), masked Stereolithography (mSLA), PolyJet (PJ), and Selective Laser Sintering (SLS). The focus was on how material type, print angle, and measurement location influenced the results. The materials used in the study included PLA, PETG, acrylic resins, PA2200, and VeroClear. Due to the optical properties of the materials used, measurements were carried out on replicas that were prepared using a RepliSet F5 silicone compound from Struers. Consequently, a methodology was developed for measuring surface roughness using the Alicona microscope based on these replicas. A 10× objective lens was used during the measurements, and the pixel size was 0.88 µm × 0.88 µm. Each time, an area of approximately 1 mm × 4 mm was measured. The lowest roughness values were observed for mSLA samples (Sa = 6.72–8.54 µm, Spk + Sk + Svk = 33.36–42.16 µm), whereas SLS exhibited the highest roughness (Sa = 27.86 µm, Spk + Sk + Svk = 183.79 µm). PJ samples exhibited intermediate roughness with significant anisotropy (Sa = 11.65 µm, Spk + Sk + Svk = 72.1 µm), which was strongly influenced by the print angle. FFF surfaces showed directional patterns and layer-dependent roughness, with the Sa parameter being the same (12.44 µm) for both PETG and PLA materials. The steepest slopes were observed for SLS surfaces (Sdq = 7.67), while mSLA exhibited the flattest microstructure (Sdq = 0.48–0.89). Statistical analysis confirmed that material type significantly influenced topography in mSLA, while print angle strongly affected PJ and FFF (although for FFF, further studies would be beneficial). The results of the research conducted can be used to develop a methodology for optimizing the printing process to achieve the required geometric surface structure. Full article

In this work we demonstrate the laser-driven reconfiguration of stripe domains in a thick bismuth-substituted iron garnet film with the (210) crystallographic orientation exhibiting strong in-plane anisotropy. Under a weak in-plane external magnetic field (H_‖), laser irradiation leads to local “twisting” of the magnetic domains; domains with opposite magnetization rotate in different directions. The twisting angle increases linearly with the in-plane magnetic field (H_‖) (above a threshold of approximately 6 Oe) and also changes linearly with the average laser intensity, being fully reversible after the irradiation process. The magnitude of the domain rotation effect does not depend on the light polarization state or its orientation. After optical irradiation, the magnetization distribution in the sample returns to its initial state. It is also observed that moving the focused beam spot along the surface can lead to irreversible modifications in the domain topology in several ways: there is a shift in the dislocations in stripe domain structure (domain “heads”) across the beam transfer direction, expanding the area with a specific magnetization vector orientation, and the stabilization of domain wall positions by their pinning on crystallographic defects. The proposed analytical model based on a local reducing of the effective anisotropy fully describes the rotation type and angle of domains and domain walls, defining their possible trajectories and certain values of the area heating or local anisotropy modulation and the rotation angles. The experimental results and the theoretical model demonstrate a thermal origin of the laser-induced effect in this type of magnetic domain structure. Full article

This research focused on the synthesis of triangular silver nanoplates (TSNPs) with sharp corners using a photomediated seed growth method. The TSNPs produced had an average edge length of 27.2 ± 9.2 nm and a (110) crystalline plane structure. In terms of optical properties, the TSNPs displayed three key absorbance peaks at approximately 400 nm, 500 nm, and 660 nm, which correspond to out-of-plane dipolar resonance, in-plane quadrupolar resonance, and in-plane dipolar resonance, respectively. The prepared TSNP colloidal solutions served as surface-enhanced Raman spectroscopy (SERS)-active materials for detecting paraquat residue in aqueous samples. We optimized the mixing time of the liquid SERS with the sample, maintaining a 1:1 volume ratio. The findings showed a remarkable enhancement of the Raman signal with 10 min mixing time using laser excitation at a wavelength of 785 nm. This study achieved the development of novel SERS-active substrates capable of detecting pesticides with excellent accuracy, sensitivity, and reproducibility for both qualitative and quantitative analysis in tap water, river water, drinking water, and cannabis water. Additionally, it paved the way for using the SERS technique as a promising approach in the areas of food safety and environmental monitoring, especially in the organic farming field. Full article

The natural frequencies and damping characterisation of a new aerospace grade composite material were investigated using a modified impulse method combined with the half power bandwidth method, which is applicable to the structures with a low damping. The composite material of interest was unidirectional carbon fibre reinforced plastic. The tests were carried out with three identical square 4.6 mm thick plates consisting of 24 plies. The composite plates were clamped along one edge in a SignalForce shaker, which applied a sinusoidal signal generated by the signal conditioner exiting the bending modes of the plates. Laser vibrometer measurements were taken at three points on the free end so that different vibrational modes could be obtained: one measurement was taken on the longitudinal symmetry plane with the other two 35 mm on either side of the symmetry plane. The acceleration of the clamp was also recorded and integrated twice to calculate its displacement, which was then subtracted from the free end displacement. Two material orientations were tested, and the first four natural frequencies were obtained in the test. Damping was determined by the half-power bandwidth method. A linear relationship between the loss factors and frequency was observed for the first two modes but not for the other two modes, which may be related to the coupling of the modes of the plate and the shaker. The experiment was also modelled by using the Finite Element Method (FEM) and implicit solver of LS Dyna, where the simulation results for the first two modes were within 15% of the experimental results. The novelty of this paper lies in the presentation of new experimental data for the natural frequencies and damping coefficients of a newly developed composite material intended for the vibration analysis of rotating components. Full article

Unidirectional guided resonances (UGRs) in periodic metasurfaces have recently attracted research interest because of their ability to achieve unidirectional radiation in all-dielectric structures without metal reflectors, which offers new possibilities for efficient grating couplers and unidirectional lasers. Here, we propose a hybrid metasurface consisting of silicon and ${\mathrm{Ge}}_2{\mathrm{Sb}}_2{\mathrm{Te}}_5$ (GST) phase change material for controlled UGR generation in the mid-infrared region. Leveraging GST’s phase-change properties to modulate the optical response of the metasurface, we achieve tunable generation of the UGR, which is demonstrated to carry a topological charge of +1. Moreover, by adjusting the degree of GST phase transition, continuous tuning of the radiation asymmetry ratio from ${10}^4$ to 1 is achieved for a specific in-plane momentum and operating wavelength. These findings offer a promising avenue for dynamically controllable UGRs, with potential applications in tunable on-chip optical couplers and light sources. Full article

Multiaxial low-cycle fatigue (MLCF) behavior of laser powder bed fused (L-PBF) Ti-6Al-4V was systematically investigated with four building direction (BD) in this paper. Proportional and non-proportional strain-controlled MLCF tests characterized cyclic softening and fracture mechanisms. L-PBF Ti-6Al-4V exhibits three-stage cyclic softening with occasional initial hardening, while non-proportional softening predominates, contrasting with conventional titanium alloys. Macro-micro characterization reveals that defect density and cleavage morphology strongly influence fatigue performance across BD. Fatigue life was predicted using analytical models (FS and KBMP) and a hybrid physics- and data-driven VAE-ANN model. While the KBMP model improves predictions over FS, both fail to fully account for BD effects. Incorporating macro-micro features, the VAE-ANN model achieves highly accurate MLCF life predictions within 10% error. These results highlight the critical roles of BD and microstructural characteristics in governing the MLCF behavior of L-PBF Ti-6Al-4V. Full article

Laser powder bed fusion (L-PBF) is an additive manufacturing technique that enables the fabrication of complex geometries through a layer-by-layer approach, overcoming limitations of conventional manufacturing. In this study, multiaxial low-cycle fatigue (MLCF) tests were conducted on L-PBF Ti-6Al-4V (Ti64) specimens built in four different orientations, selected based on critical plane orientations identified from rolled titanium. Under proportional strain-controlled loading, the cyclic softening behavior, mean stress response, and fracture mechanisms of the material were systematically investigated. The results show that L-PBF Ti64 exhibits a three-stage softening characteristic (continuous softening, stable, and rapid softening). Fatigue cracks primarily initiate from inner-surface lack-of-fusion defects. Crack propagation shows cleavage and quasi-cleavage characteristics with tearing ridges, river patterns, and multi-directional striations. Proposed KBMP life prediction model, incorporating λ and building direction parameters, was developed. The KBMP-λ model demonstrates optimal accuracy, providing a reliable tool for the design of L-PBF titanium components subjected to complex multiaxial fatigue loading with relative errors within 20%. Full article

The ATLAS lidar on NASA’s Earth-orbiting ICESat-2 satellite has operated continuously since its launch in September 2018, with no sign of degradation. Compared to previous international single-beam spaceborne lidars, which operated at a few tens of Hz, the single-photon-sensitive, six-beam ATLAS pushbroom lidar provides 60,000 surface measurements per second and has accumulated almost 3 trillion surface measurements during its six years of operation. It also features a 0.5 m² telescope aperture and a single, 5 Watt, frequency-doubled Nd:YAG laser generating a 10 KHz train of 1.5-nanosecond pulses at a green wavelength of 532 nm. The current paper investigates how, with minor modifications to the ATLAS lidar, this capability might be extended to other planets within our solar system. Crucial to this capability is the need to minimize the solar background seen by the lidar while simultaneously providing, for long time intervals (multiple months), an uninterrupted, modestly powered, multimegabit per second interplanetary laser communications link to a terminal in Earth orbit. The proposed solution is a pair of Earth and planetary satellites in high, parallel, quasi-synchronized orbits perpendicular to their host planet’s orbital planes about the Sun. High orbits significantly reduce the time intervals over which the interplanetary communications link is blocked by their host planets. Initial establishment of the interplanetary communications link is simplified during two specific time intervals per orbit when the sunlit image of the two planets are not displaced from their actual positions (“zero point ahead angle”). In this instance, sunlit planetary images and the orbiting satellite laser beacon can be displayed on the same pixelated detector array, thereby accelerating the coalignment of the two communication terminals. Various tables in the text provide insight for each of the eight planets regarding the impact of solar distance on the worst-case Signal-to-Noise Ratio (SNR), the effect of satellite orbital height on the duration of the unblocked interplanetary communications link, and the resulting planetary surface continuity and resolution in both the along-track and cross-track directions. For planets beyond Saturn, the laser power and/or transmit/receive telescope apertures required to transmit multimegabit-per-second lidar data back to Earth are major challenges given current technology. Full article

Rutting is a critical form of pavement distress that compromises driving safety and long-term structural integrity. Traditional detection methods predominantly rely on cross-sectional measurements and high-cost inertial navigation-assisted laser scanning, which limits their applicability for large-scale, full-section evaluation. To address these limitations, this study proposes a framework for full-section rutting detection leveraging an area-array structured light camera for efficient 3D data acquisition. A multi-scale texture enhancement strategy based on 2D wavelet transform is introduced to extract latent surface features, enabling robust and accurate point-cloud registration without the need for artificial markers. Additionally, an improved Random Sample Consensus—Density-Based Spatial Clustering of Applications with Noise (RANSAC-DBSCAN) algorithm is designed to enhance the precision and robustness of rutting region segmentation under real-world pavement conditions. The proposed method is experimentally validated using 102 multi-frame pavement point clouds. Compared to Fast Point Feature Histograms (FPFH) and Deep Closest Point (DCP), the registration approach achieves a 71.31% and 80.64% reduction in point-to-plane error, respectively. For rutting segmentation, the enhanced clustering method attains an average F1-score of 90.5%, outperforming baseline methods by over 15%. The proposed workflow can be seamlessly integrated into vehicle-mounted structured-light inspection systems, offering a low-cost and scalable solution for near real-time, full-lane rutting detection in routine pavement monitoring. Full article

This article demonstrates how the non-intrusive techniques PLIF (Planar Laser-Induced Fluorescence) and PIV (Particle Image Velocimetry) are used to study fluid flow and mixing in a water model of a continuous casting tundish. These techniques validate CFD models by providing hydrodynamic data and by testing the models’ ability to predict mixing through simulated concentration field evolution under defined process conditions. Using PIV and PLIF yields more accurate information on turbulent mixing and impurity transport than traditional methods. Access to flow and concentration field evolution enables more precise mathematical model refinement and clarifies the impact of tundish design or operational changes on hydrodynamics and mixing. Relative errors in chemical evolution are approximately 20%, whereas velocity errors vary depending on the measurement plane, being lower for longitudinal planes and higher for transversal planes. This suggests that the turbulence model does not fully capture all low- and high-velocity zones. This approach supports reliable flow and mixing predictions in metallurgy and related fields. Full article

Sapphire crystals, owing to their outstanding mechanical and optical properties, which are widely used in advanced optics, microelectronic devices, and medical instruments. The manufacturing precision of sapphire optical components critically affects the performance of advanced optical systems. However, the extremely high hardness and low fracture toughness of sapphire make it a typical hard-to-machine material, prone to brittle surface fractures and subsurface damage during material removal. Improving the machinability of sapphire remains a pressing challenge in advanced manufacturing. In this study, surface modification and enhanced ductility of C-plane sapphire were achieved via ion implantation, and the machinability of the modified sapphire was further improved through laser-assisted diamond machining (LADM). Monte Carlo simulations were employed to investigate the interaction mechanisms between incident ions and the target material. Based on the simulation results, phosphorus ion implantation experiments were conducted, and transmission electron microscopy observation was used to characterize the microstructural evolution of the modified layer, while the optical properties of the samples before and after modification were analyzed. Finally, groove cutting experiments verified the enhancement in ductile machinability of the modified sapphire under LADM. At a laser power of 16 W, the ductile–brittle transition depth of the modified sapphire increased to 450.67 nm, representing a 51.57% improvement over conventional cutting. The findings of this study provide valuable insights for improving the ductile machining performance of hard and brittle materials. Full article

Azimuth sensing plays a vital role in numerous industrial applications where tilt angle serves as a key parameter. To address the demand for accurate and reliable measurements, we propose an all-fiber two-dimensional inclinometer based on the Vernier effect in a multi-core fiber Fabry–Perot interferometer. The sensor is capable of simultaneously measuring both inclination and azimuth angles with high accuracy. A cascaded Fabry–Perot interferometer was inscribed in a seven-core fiber using a femtosecond laser plane-by-plane direct writing technique. By monitoring the wavelength shifts in two peripheral cores, we demonstrated the feasibility and performance of the proposed sensor. The experimental results showed that the inclinometer exhibited high sensitivity, with maximum values of −0.5272 nm/° for azimuth measurement (maximum measurement error: 7.33°) and −0.5557 nm/° for inclination measurement (maximum measurement error: 5.97°). The measurement ranges extended from 0° to 360° for azimuth and from –90° to 90° for inclination. Owing to its wide measurement range, compact structure, and high sensitivity, the proposed all-fiber two-dimensional inclinometer holds significant potential for practical applications. Full article

Zirconium (Zr) thin films were deposited on silicon (Si) substrates via pulsed laser deposition (PLD) using a 248 nm excimer laser. The effects of substrate temperature on film morphology and crystallinity were systematically investigated. X-ray diffraction (XRD) revealed that the Zr(100) plane exhibited the strongest orientation at 400 °C while Zr (002) was maximum at 500 °C. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) analyses demonstrated an increase in surface roughness with temperature, with the smoothest surface observed at lower temperatures and significant island formation at 500 °C due to the transition to 3D growth. At 500 °C, interdiffusion effects led to the formation of zirconium silicide at the Zr/Si interface. To further interpret the experimental findings, computational modeling was employed to analyze the transition from 2D layer-by-layer growth to 3D island formation at elevated temperatures. Using a multi-parameter kinetics-free model based on free energy minimization, the critical film thickness for this transition was determined to be ~1–2 nm, aligning well with experimental observations. A separate kinetic model of island nucleation and growth predicts that this shift is driven by the kinetics of adatom surface diffusion. Additionally, the kinetic simulations revealed that, at 400 °C, adatom diffusivity optimally balances crystallization and surface energy minimization, yielding the highest film quality. At 500 °C, the rapid increase in diffusivity leads to the proliferation of 3D islands, consistent with the roughness trends observed in SEM and AFM data. These findings underscore the critical role of deposition parameters in tailoring Zr thin films for applications in advanced coatings and electronic devices. Full article

This work presents the development of a Z-depth system for Confocal Raman Spectroscopy (CRS), which allows for the acquisition of Raman spectra both at the surface and at depth profile in heterogeneous samples. The proposed CRS system consists of the coupling of a commercial 785 nm Raman Probe Bifurcated (RPB) with a 20x/0.40 infinity plan achromatic polarizing microscope objective, a Long Working Distance (LWD) of 1.2 cm, and a 50 μm core-multimode optical fiber used as a pinhole filter. With this implementation, it is possible to achieve both a high spatial resolution of approximately 16.2 μm and a spectral resolution of ∼14 cm⁻¹, which is determined by the FWHM of the thin 1004 cm⁻¹ Raman profile band. The system is configured to operate within 400–1800 cm⁻¹ spectral windows. The implementation of a system of this nature offers a favorable cost–benefit ratio, as commercial CRS is typically found in high-cost environments such as cosmetics, pharmaceutical, and biological laboratories. The proposed system is low-cost and employs a minimal set of optical components to achieve functionality comparable to that of a confocal Raman microscope. High signal-to-noise ratio (SNR) Raman spectra (∼660.05 at 1447 cm⁻¹) can be obtained with short integration times (∼25 s) and low laser power (30–35 mW) when analyzing biological samples such as in vivo human fingernails and fingertips. This power level is significantly lower than the exposure limits established by the American National Standards Institute (ANSI) for human laser experiments. Raman spectra were recorded from the surface of both the nails and fingertips of three volunteers, in order to characterize their biological samples at different depths. The measurements were performed in 50 μm steps to obtain molecular structural information from both surface and subsurface tissue layers. The proposed CRS enables the identification of differences between two closely spaced, centered, and narrow Raman bands. Additionally, broad Raman bands observed at the skin surface can be deconvolved into at least three sub-bands, which can be quantitatively characterized in terms of intensity, peak position, and bandwidth, as the confocal plane advances in depth. Moreover, the CRS system enables the detection of subtle, low-intensity features that appear at the surface but disappear beyond specific depth layers. Full article

Epoxy resins are valuable in aerospace, electronics, and high-performance industries; however, their inherently low thermal conductivity (TC) limits applications requiring effective heat dissipation. Recent reports suggest that certain liquid crystalline or partially crystalline epoxy formulations can achieve higher TC, even exceeding 1 W/(m·K). To investigate this, 17 epoxy formulations were prepared, including the commonly used diglycidyl ether of bisphenol A (DGEBA) and two custom-synthesized diepoxides: TME4, which contains rigid aromatic ester linkages with a C4 aliphatic spacer, and LCE-DP, featuring rigid imine bonds. Thermal conductivity was measured using four techniques: laser flash analysis (LFA), modified transient plane source (MTPS), time-domain thermoreflectance (TDTR), and displacement thermo-optic phase spectroscopy (D-TOPS). Additionally, small-angle and wide-angle X-ray scattering (SAXS/WAXS) were performed to detect crystalline or liquid crystalline domains. All formulations exhibited TC values ranging from 0.13 to 0.32 W/(m·K). The TME4–DDS systems, previously reported to be near 1 W/(m·K), consistently measured between 0.26 and 0.30 W/(m·K). Thus, under our synthesis and curing conditions, the elevated TC reported in prior studies was not reproduced, and no strong evidence of crystallinity was observed; indications of local ordering did not translate into higher conductivity. Variations in TC among methods often matched or exceeded the gains attributed to mesophase formation. More broadly, evidence for crystallinity in epoxy thermosets appears weak, consistent with the notion that crosslinking suppresses long-range ordering. Full article