Search Results (807)

The rapid advancement of high-performance electronics has intensified the demand for wide-bandgap semiconductor materials capable of operating under high-power and high-temperature conditions. Among these, silicon carbide (SiC) has emerged as a leading candidate due to its superior thermal conductivity, chemical stability, and mechanical strength. However, the high cost and complexity of SiC wafer fabrication, particularly in slicing and exfoliation, remain significant barriers to its widespread adoption. Conventional methods such as wire sawing suffer from considerable kerf loss, surface damage, and residual stress, reducing material yield and compromising wafer quality. Additionally, techniques like smart-cut ion implantation, though capable of enabling thin-layer transfer, are limited by long thermal annealing durations and implantation-induced defects. To overcome these limitations, ultrafast laser-based processing methods, including laser slicing and stealth dicing (SD), have gained prominence as non-contact, high-precision alternatives for SiC wafer exfoliation. This review presents the current state of the art and recent advances in laser-based precision SiC wafer exfoliation processes. Laser slicing involves focusing femtosecond or picosecond pulses at a controlled depth parallel to the beam path, creating internal damage layers that facilitate kerf-free wafer separation. In contrast, stealth dicing employs laser-induced damage tracks perpendicular to the laser propagation direction for chip separation. These techniques significantly reduce material waste and enable precise control over wafer thickness. The review also reports that recent studies have further elucidated the mechanisms of laser–SiC interaction, revealing that femtosecond pulses offer high machining accuracy due to localized energy deposition, while picosecond lasers provide greater processing efficiency through multipoint refocusing but at the cost of increased amorphous defect formation. The review identifies multiphoton ionization, internal phase explosion, and thermal diffusion key phenomena that play critical roles in microcrack formation and structural modification during precision SiC wafer laser processing. Typical ultrafast-laser operating ranges include pulse durations from 120–450 fs (and up to 10 ps), pulse energies spanning 5–50 µJ, focal depths of 100–350 µm below the surface, scan speeds ranging from 0.05–10 mm/s, and track pitches commonly between 5–20 µm. In addition, the review provides quantitative anchors including representative wafer thicknesses (250–350 µm), typical laser-induced crack or modified-layer depths (10–40 µm and extending up to 400–488 µm for deep subsurface focusing), and slicing efficiencies derived from multi-layer scanning. The review concludes that these advancements, combined with ongoing progress in ultrafast laser technology, represent research opportunities and challenges in transformative shifts in SiC wafer fabrication, offering pathways to high-throughput, low-damage, and cost-effective production. This review highlights the comparative advantages of laser-based methods, identifies the research gaps, and outlines the challenges and opportunities for future research in laser processing for semiconductor applications. Full article

Wafer-level thin-film stress measurement is essential for reliable semiconductor fabrication. However, existing techniques present limitations in practice. Interferometry achieves high precision but at a cost that becomes prohibitive for large wafers. Meanwhile laser-scanning systems are more affordable but can only provide sparse data points. This work develops a phase-measuring deflectometry (PMD) system to bridge this gap and deliver a full-field solution for wafer stress mapping. The implementation addresses three key challenges in adapting PMD. First, screen positioning and orientation are refined using an inverse bundle-adjustment approach, which performs multi-parameter optimization without re-optimizing the camera model and simultaneously uses residuals to quantify screen deformation. Second, a backward-propagation ray-tracing framework benchmarks two iterative strategies to resolve the slope-height ambiguity which is a fundamental challenge in PMD caused by the absence of a fixed optical center on the source side. The reprojection constraint strategy is selected for its superior convergence precision. Third, this strategy is integrated with regional wavefront reconstruction based on Hermite interpolation to effectively eliminate edge artifacts. Experimental results demonstrate a peak-to-valley error in the reconstructed topography of 0.48 µm for a spherical mirror with a radius of 500 mm. The practical utility of the system is confirmed through curvature mapping of a 12-inch patterned wafer and further validated by stress measurements on an 8-inch bare wafer, which show less than 5% deviation from industry-standard instrumentation. These results validate the proposed PMD method as an accurate and cost-effective approach for production-scale thin-film stress inspection. Full article

Modeling elementary diffusion processes in nanostructured materials is essential for developing platforms capable of interacting with high-speed physical signals. In this work, the photothermal response of a nano-hydroxyapatite/carbon nanotube (nHAp/CNT) composite was experimentally characterized and modeled through a cellular automaton (CA) framework designed to capture the thermal propagation of the hybrid system. Synthesizing nHAp/CNT composites enables the combination of the biocompatible and piezoelectric nature of nHAp with the enhanced photothermal response introduced by CNTs. UV–Vis reflectance measurements confirmed that CNT incorporation increases the optical absorption of the ceramic matrix, resulting in more efficient photothermal conversion. The composite was irradiated with a nanosecond pulsed laser, and the resulting thermal transients were compared with CA simulations based on a D2Q9 lattice configuration. The model accurately reproduces experiments, achieving R² > 0.991 and NRMSE below 2.4% for all tested laser powers. This strong correspondence validates the CA approach for predicting spatiotemporal heat diffusion in heterogeneous nanostructured composites. Furthermore, the model revealed a sensitive thermal coupling when two heat sources were considered, indicating synergistic enhancement of local temperature fields. These findings demonstrate both the effective integration of CNTs within the nHAp matrix and the capability of CA-based modeling to describe their photothermal behavior. Overall, this study establishes a computational–experimental basis for designing controlled thermal-wave propagation and guiding future multi-frequency or multi-source photothermal mixing experiments. Full article

In this study, TiB₂/AlSi10Mg, 2 wt.% SiC + TiB₂/AlSi10Mg, and 5 wt.% SiC + TiB₂/AlSi10Mg composite powders were prepared via high-energy ball milling. For the first time, TiB₂ and SiC hybrid particle-reinforced aluminum matrix composites (AMCs) were fabricated using the Laser-Directed Energy Deposition (LDED) technique. The effects of processing parameters on the microstructure evolution and mechanical properties were systematically investigated. Using areal energy density as the main variable, the experiments combined microstructural characterization and mechanical testing to elucidate the underlying strengthening and failure mechanisms. The results indicate that both 2 wt.% and 5 wt.% SiC + TiB₂/AlSi10Mg composites exhibit excellent formability, achieving a relative density of 98.9%. However, the addition of 5 wt.% SiC leads to the formation of brittle Al₄C₃ and TiC phases within the matrix. Compared with the LDED-fabricated AlSi10Mg alloy, the tensile strength of the TiB₂/AlSi10Mg composite increased by 21.4%. In contrast, the tensile strengths of the 2 wt.% and 5 wt.% SiC + TiB₂/AlSi10Mg composites decreased by 3.7% and 2.6%, respectively, mainly due to SiC particle agglomeration and the consumption of TiB₂ particles caused by TiC formation. Nevertheless, their elastic moduli were enhanced by 9% and 16.3%, respectively. Fracture analysis revealed that the composites predominantly exhibited ductile fracture characteristics. However, pores larger than 10 μm and SiC/TiB₂ clusters acted as crack initiation sites, inducing stress concentration and promoting the propagation of secondary cracks. Full article

Pax6 plays a highly conserved role in the formation of the eye, development, and patterning of the nervous system across bilaterians. Nevertheless, there are no studies focusing on the role of Pax6 during asexual reproduction, a developmental trajectory that is widespread among metazoans. The present study represents the first investigation of Pax6 gene expression during agametic propagation in annelids. We identified in the asexually reproducing annelid Nais communis four homologs of Pax6 and examined their developmental patterns by in situ hybridization. To establish a morphological basis for the expression patterns, we used immunohistochemistry and confocal laser scanning microscopy to describe the nervous system architecture of the growing adults and remodeling of the original ventral nerve cord, development of the new brain, ventral ganglia, peripheral nerves, and sensory organs in asexually reproducing worms. Our results support the hypothesis of an evolutionarily conserved function of Pax6 genes in the development of the eye and other sensory organs, as well as the central nervous system, among bilaterians, regardless of developmental trajectory. On the other hand, identified Pax6 homologs show differential expression within the developing new head and tail ends. Differences in spatiotemporal expression patterns may be evidence of functional diversification of duplicated homologs. Full article

With the widespread application of fiber laser technology in industries, communications, medical fields, and beyond, the demand for controlling the spatial modes of their output beams has been increasingly growing. Traditional mode control methods are constrained by factors such as device power thresholds, system complexity, and cost, making it difficult to meet the requirements for high-power, high-purity, and rapidly switchable multimode regulation. This paper reviews adaptive mode control technology based on photonic lanterns (PLs). By integrating ideas from adaptive optics and photonics, this technology utilizes photonic lanterns to achieve efficient mode evolution from single-mode to multimode fibers. Combined with optimization algorithms, it enables real-time regulation of input phases, thereby producing stable, high-purity target modes or mode superposition fields at the multimode output end. The paper systematically introduces the structural classifications, propagation characteristics, and fabrication processes of photonic lanterns, as well as the mode evolution mechanisms in different types of photonic lanterns. It elaborates in detail on the structural design, algorithm implementation, and experimental validation of the adaptive control system based on photonic lanterns. Furthermore, it explores the application prospects of this technology in areas such as suppressing transverse mode instability, mode-division multiplexing communications, particle manipulation, and high-resolution spectral measurements. The results demonstrate that the all-fiber adaptive mode control system based on photonic lanterns offers advantages such as compact structure, low loss, fast response, and strong scalability. Full article

Cracks were found at the gate of the 430Cb ferritic stainless steel exhaust system jet base produced by investment casting. In this paper, the cracks of failed stainless steel castings were comprehensively analyzed by means of macroscopic inspection, laser confocal microscopy, field emission scanning electron microscopy, electron backscatter diffraction, X-ray diffractometer, ProCAST (version 2018, ESI Group, Paris, France) simulation and Thermo-Calc (TCFE10 database, 2022a, Thermo-Calc Software AB, Solna, Sweden) thermodynamic calculation. It can be concluded that all the cracks originate from the gate on the surface of the casting, and the fracture surface shows brittle intergranular characteristics, which can be determined as cold cracks. The formation of cold cracks can be attributed to the fact that the local stress generated during cooling after the casting solidifies exceeds the strength limit of the material itself. As the gate is the final solidification zone, shrinkage is limited and stress is concentrated. The grains are coarse, and the microstructure defects such as shrinkage porosity, pores and needle-like NbC further weaken the plasticity of the grain boundaries, promoting the crack to propagate along the direction of the maximum principal stress. The uneven cooling rate and shell constraint during the investment casting process make it difficult to release stress, and the existence of microstructure defects are the fundamental causes of crack generation. Full article

Owing to their superior performance in countering electromagnetic interference on the battlefield, laser fuzes have become a promising candidate for application in munition systems. However, as the short-pulse laser is activated by an electrical signal, the possibility of accidental emissions caused by logic device failure cannot be ruled out, making it vulnerable under the effects of strong electromagnetic coupling. Integrating an encrypted, MEMS-based Safety and Arming Device (SAD) into the energy channel to control the propagation of short-pulse lasers can significantly enhance the safety level of munition systems. In the present work, the effect of MEMS SAD integration on laser propagation is investigated. The results demonstrate that the insertion of a MEMS SAD does not introduce significant attenuation of short-pulse laser propagation. A firing test is conducted using the laser-driven flyer detonator to verify the safety, charging mechanism, and function to provide a comprehensive characterization of the laser fuze. To guarantee the initiation of insensitive explosives, the coupling efficiency and laser transmission energy density of multi-mode quartz fibers are studied. Full article

To address the significant challenges associated with achieving precise target tracking and engagement of high-energy laser systems operating under complex atmospheric conditions, this study proposes an indirect detection strategy based on the characteristics of the laser spot. The core principle of this method involves analyzing the two-dimensional scattered-spot distribution formed after the laser beam interacts with the target surface, encompassing morphological variations and energy concentration patterns to indirectly characterize of target surface features. Furthermore, a multidimensional coupled model was developed, integrating atmospheric transmission effects, tracking-strike errors, and strike efficiency. This model is designed to systematically enhance the laser system’s tracking accuracy and strike effectiveness evaluation by incorporating the attenuation and distortion of laser propagation through atmospheric turbulence and aerosols, along with tracking and pointing error algorithms. The research quantifies the influence of atmospheric factors (such as visibility and turbulence intensity) on laser propagation and further elucidates how these parameters impact tracking and strike effectiveness, thereby offering new technical insights for target perception and performance evaluation of laser systems operating under complex environmental conditions. Full article

Laser-induced acoustic (LIA) underwater detection, as a next-generation sensing paradigm, combines high spatial resolution, rapid temporal response, and cross-medium detection capability, positioning it as a strategically significant technology in marine resource exploration, military security, and ocean environmental monitoring. The fundamental principles underlying LIA technology are systematically examined, together with recent advances in representative experimental systems and critical enabling techniques. The characteristics of the laser–acoustic transmission channel are comprehensively investigated, and the mechanisms through which laser parameters modulate the properties of acoustic signals are rigorously elucidated. Moreover, several challenges hindering practical applications are underscored, including laser energy attenuation, interference arising from complex underwater environments, and the comparatively high cost of equipment. Finally, future research directions are outlined, encompassing the development of high-efficiency laser sources, multimodal integrated sensing strategies, intelligent signal processing algorithms, and improved environmental adaptability. These efforts are intended to provide theoretical underpinnings for the continued advancement and broader application of LIA-based underwater detection technologies. Full article

We present a time-dependent framework that combines a hybrid basis, consisting of Gaussian-type orbitals (GTOs) and finite-element discrete-variable representation (FEDVR) functions, with a multicenter grid to simulate strong-field and attosecond dynamics in atoms and molecules. The method incorporates the construction of the orthonormal hybrid basis, the evaluation of electronic integrals, a unitary time-propagation scheme, and the extraction of optical and photoelectron observables. Its accuracy and robustness are benchmarked on one-electron systems such as atomic hydrogen and the dihydrogen cation (${\mathrm{H}}_2^{+}$) through comparisons with essentially-exact reference results for bound-state energies, high-harmonic generation spectra, photoionization cross sections, and photoelectron momentum distributions. This work establishes the groundwork for its integration with quantum-chemistry methods, which is already operational but will be detailed in future work, thereby enabling ab initio simulations of correlated polyatomic systems in intense ultrafast laser fields. Full article

A coupled discrete element method and computational fluid dynamics (DEM-CFD) approach was utilized to systematically investigate the mesoscale dynamics of single-track melt pools in laser powder bed fusion (LPBF) of TiAl-based composites. It was found that the melt pool’s temporal evolution and flow behavior are predominantly governed by recoil pressure and Marangoni convection. When lower laser power and higher scanning speeds are applied, the melt pool size is limited due to restricted energy input, resulting in increased cooling rates and steeper temperature gradients. Under these conditions, residual stresses are slightly elevated. However, crack initiation and propagation are partially suppressed by the refined microstructure formed during rapid cooling, unless a critical stress threshold is surpassed. In contrast, the use of higher laser power with lower scanning speeds leads to the formation of wider and deeper melt pools and an expanded heat-affected zone, where cooling rates and temperature gradients are reduced. Under these circumstances, significant recoil pressure induces interfacial instabilities and surface perturbations, thereby considerably increasing the likelihood of cracking. The reliability of the developed model was confirmed by the close agreement between the simulation results and experimental data. Full article

Composite materials are widely utilized for their excellent properties; however, the mismatch in phase response during processing often induces surface and subsurface damage. While reducing the cutting depth is a common strategy to improve quality, it shifts the material removal mechanism from shear to ploughing–extrusion, which can, in fact, degrade the final surface integrity. Energy field assistance is a promising approach to suppress this issue, yet its underlying mechanism remains insufficiently understood. This study investigates high-silicon aluminum alloy by combining turning experiments with molecular dynamics simulations to elucidate the origin and evolution of damage under different energy fields, establishing a correlation between microscopic processes and observable defects. In conventional turning, damage propagation is driven by particle accumulation and dislocation interlocking. Ultrasonic vibration softens the material and confines plastic deformation to the near-surface region, although excessively high transient peaks can lead to process instability. Laser remelting turning disperses stress within the remelted layer, significantly inhibiting defect expansion, but its effectiveness is highly sensitive to variations in cutting depth. The hybrid approach, laser remelting ultrasonic vibration turning, leverages the dispersion buffering effect of the remelted layer and the localized plastic deformation from ultrasonication to reduce peak loads, control deformation depth, and suppress defects, while simultaneously mitigating the depth sensitivity of damage and maintaining removal efficiency. This work clarifies the mechanism by which a composite energy field controls damage in the micro-cutting of high-silicon aluminum alloy, providing practical guidance for the high-quality machining of composite materials. 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

Ischemia–reperfusion is a rapidly evolving cascade that involves a variety of metabolic shifts whose precise timing and sequential order are still poorly understood. Clarifying these dynamics is critical for understanding the core injury trajectory of stroke and for refining time-delimited therapeutic interventions. More broadly, continuous in situ monitoring of the middle-cerebral-artery occlusion process at the system level has not yet been achieved. Here, we report the first single-subject high-resolution spatiotemporal resolution metabolic maps of the ultra-early phase of ischemic stroke in a rodent model. Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) imaging mapped a metabolic abnormality area in the ischemic hemisphere that propagates from the striatum to the cortex. Microdialysis probes were then stereotaxically implanted within this metabolic abnormality area, capturing 10,429 metabolites that resolved into 16 temporally distinct trajectories aligned with probe insertion, ischemic injury, and reperfusion injury. Analysis of specific metabolic pathways mainly revealed that the delayed clearance of metabolic waste (urea and tryptamine) during early reperfusion, the transient attenuation of the citrate-to-oxaloacetate buffering gradient within the TCA cycle, and the accumulation of extracellular branched-chain amino acids all play crucial roles in shaping the injury trajectory. Simultaneously, the depletion of cellular repair mechanisms (pyrimidine synthesis) in the early phase of reperfusion also warrants our attention. These findings provide novel insights into the molecular basis and mechanisms of ischemia–reperfusion and offer a comprehensive resource for further investigation. Full article