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Study of the physicochemical surface alterations and incubation phenomena induced on iron targets by nanosecond pulsed laser ablation in liquids: Effect on productivity and characteristics of the synthesized nanoscale zero-valent iron (nZVI) particles
摘要： This work presents a systematic study of the significant role of the surface physicochemical alterations produced during the laser ablation of massive iron disks submerged in different solvents on the generation of colloidal iron nanoparticles. For that purpose, the laser ablation thresholds and the incubation coefficients for various pulse numbers per site and pulse energies have been measured under distilled water (DW) and ethanol (EtOH). After that, a complete physicochemical characterization of these targets indicated higher threshold fluence values for the ablation experiments conducted in EtOH than those performed in DW. The threshold fluence values decreased also with the decrease of the pulse overlap for both solvents, being it much more pronounced in EtOH. In addition, the related incubation coefficient showed that the incubation effect is lower for experiments conducted in DW. The characteristics of the synthesized nZVI particles were also a function of the solvent nature and the pulse overlap: laser ablation in DW leaded to iron oxide nanoparticles, whereas core-shell iron nanoparticles were obtained in EtOH. Moreover, high pulse overlap values lead to chemical alterations, resulting in a decrease of the composition homogeneity and a strong increase of the nanoparticle polydispersity.
关键词： Incubation effect,Nanosecond pulsed laser ablation in liquids,Raman spectroscopy,Colloidal nanoscale zero-valent iron particles,Laser ablation threshold,Laser induced-chemical surface alteration
更新于2025-09-19 17:13:59
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Locally Controllable Surface Foaming of Polymers Induced by Graphene via Near-Infrared Pulsed Laser
摘要： Our study proposed an e?cient and environment-friendly strategy to realize the locally controllable surface foaming on polymers via a near-infrared pulsed laser. This laser foaming was induced by the multilayer graphene (MLG), and only 0.05 wt % MLG gave the polymer an excellent foaming performance with good smoothness and a foaming height of 0.41 mm. Bene?ted from programming and automatically controlling the laser system, foamed patterns of arbitrary shapes with three-dimensional appearance could be accurately written on the polymer surface. Scanning electron microscopy con?rmed that the uniform cells produced by laser foaming were mainly ellipsoidal with closed-cell structures (D = 31.5 μm); moreover, the surface foam had three layers with a total thickness of 633.7 μm. X-ray photoelectron spectroscopy (XPS) revealed the surface carbonization of the foam during laser foaming. Both attenuated total re?ection Fourier transform infrared spectroscopy and XPS con?rmed the weak oxidation of the polypropylene (PP) matrix caused by laser because of the appearance of C?O and CO groups on foams. Besides, the Raman depth imaging demonstrated the layered carbonization distribution in the foam surface. The micro-Raman spectroscopy con?rmed that the amorphous carbon and the sp/sp2 carbon (CC/CC) were two main carbonized products of PP. This study also proposed the mechanism of polymer laser foaming induced by MLG.
关键词： near-infrared pulsed laser,polymer,laser foaming,laser writing,multilayer graphene
更新于2025-09-19 17:13:59
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Effect of liquid environment on single-pulse generation of laser induced periodic surface structures and nanoparticles
摘要： The effect of a liquid environment on the fundamental mechanisms of surface nanostructuring and generation of nanoparticles by single pulse laser ablation is investigated in a closely integrated computational and experimental study. A large-scale molecular dynamics simulation of spatially-modulated ablation of Cr in water reveals a complex picture of dynamic interaction between the ablation plume and water, which involves rapid deceleration of the ablation plume by water environment, formation and prompt disintegration of a hot metal layer at the interface between the ablation plume and water, lateral redistribution and redeposition of a major fraction of the ablation plume, and eventual formation of smooth frozen surface features. A good agreement between the shapes of the surface features predicted in the simulation and the ones generated in single pulse laser ablation experiments performed for Cr in water supports the mechanistic insights revealed in the simulations. The results of this study suggest that the presence of liquid environment can eliminate the sharp features of surface morphology, reduce the amount of material removed from the target by more than an order of magnitude, and narrow down the nanoparticle size distribution as compared to laser ablation in vacuum. Moreover, the computational predictions of the effective incorporation of molecules constituting the liquid environment into the surface region of the irradiated target and the generation of high vacancy concentrations exceeding the equilibrium levels by more than an order of magnitude suggest a potential for hyperdoping of laser-generated surfaces by solutes present in the liquid environment.
关键词： Laser-Induced Periodic Surface Structures (LIPSS),Generation of Nanoparticles,Crystal Defects,Surface Morphology,Hyperdoping,Molecular Dynamics Simulations,Pulsed Laser Ablation in Liquids
更新于2025-09-19 17:13:59
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Experimental and Numerical Study of AISI 4130 Steel Surface Hardening by Pulsed Nd:YAG Laser
摘要： Laser surface transformation hardening (LSTH) of AISI 4130 was investigated by a Nd:YAG pulsed laser. Laser focal height (LFH), pulse width (LPW), scanning speed (LSS), and power (LP) varied during the experiments. The microstructure of the treated zone was characterized by optical (OM) and field emission scanning electron microscopy (FESEM). Micro-hardness was measured in the width and depth directions. Results showed that the hardness and depth of hardened layer increased by decreasing the LSS and the laser focal position (LFP), and by increasing the LPW. The results were compared with those obtained by furnace heat treatment of the same steel. Eventually, a finite element model was employed for the simulation of the LSTH of AISI 4130 steel and calculation of the heat-treated zone. The results showed that the model can predict with accuracy the temperature profile and the size and the shape of the laser hardened region.
关键词： Nd:YAG pulsed laser,laser surface transformation hardening,FEM model,AISI 4130 steel
更新于2025-09-19 17:13:59
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Pulsed laser irradiation of a nanoparticles sensitised RDX crystal
摘要： The laser initiation of secondary explosives presents tactical, safety and environmental advantages over traditional ignition systems utilising primary explosives. In this paper, direct ignition or initiation by pulsed laser was investigated of cyclotrimethylenetrinitramine (RDX) crystals doped with gold nanoparticles (GNPs) for the first time. A nano-seconds pulsed laser was used for direct irradiation of the crystals at the GNP’s surface-plasmon-resonance wavelength of 532 nm. RDX crystals were recrystallised from a solution containing GNPs and characterised by visual microscopy for surface coating and subsurface doping. A high-speed camera was used to observe and capture the modes of interaction between the GNPs-doped RDX crystals and pulsed laser irradiation with a new classification method. Laser fluence thresholds for ignition and initiation were established. The GNPs sensitized RDX to pulsed laser irradiation at this selected wavelength is 3 orders of magnitude more sensitive than pure RDX. Direct initiation of the GNPs doped RDX crystal at laser fluence of 0.04 J/cm 2 led to the total consumption of a crystal sample, which was unreproducible with pure RDX. The results show that GNPs are effective optical sensitizers for direct initiation of RDX crystal by low-power pulsed laser.
关键词： Gold nanoparticles,Pulsed laser,Explosive,Laser ignition
更新于2025-09-19 17:13:59
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Modified laser‐fired contact process for efficient PERC solar cells
摘要： A laser‐fired contact (LFC) process is one of the techniques for making local electrical contacts at the rear side of passivated emitter and rear cell (PERC) solar cells. In the LFC process, opening of the passivated dielectric layers and alloying of Si and Al need to be made in a single step laser process. For this reason, the LFC process is accompanied by the loss of Al and the laser damage to the Si wafer. In this study, we present a novel multistep LFC process combining the conventional LFC and laser‐induced forward transfer (LIFT) processes. The modified LFC scheme we proposed consists of three steps: (a) opening of the passivation layers and partial alloying of Al‐Si, (b) additional deposition of Al on the local contact holes, and (c) post laser firing of the transferred Al. Applying the modified LFC process to the PERC cells of 1.0 cm2 of area, we demonstrate the effective recombination velocity of the laser‐processed wafers can be remarkably reduced while maintaining the low contact resistance. The best of the PERC solar cell fabricated by the modified LFC process exhibited an efficiency of 19.5% while the conventional LFC‐PERC cell showed 18.6%. The efficiency gains of the modified LFC‐PERC cells was largely contributed by the enhanced open circuit voltage (Voc) and fill factor (FF).
关键词： contact resistance,crystalline silicon solar cells,PERC cell,pulsed laser,laser‐fried contact,implied Voc
更新于2025-09-19 17:13:59
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Development of a novel system for in-situ repair of aeroengine airfoil via pulsed laser ablation
摘要： A novel system for performing in-situ micro-machining of aero-engines for repair applications is proposed in this paper. Using Pulsed Laser Ablation (PLA) as material removal technique, surface cracks caused by foreign objects colliding with airfoils are removed by performing a layer-by-layer micro-machining in the area surrounding the damaged zone. Compared to conventional repair performed by micro-grinding, our invasive PLA system demonstrates a similar level of performance, evaluated from the point of view of fatigue strength in the high cycle (> 107) regime. The follow-up fractographic and metallurgical analysis, indicated that although some micro-structural characteristics are different between the repair methods, the incurred surface damage is limited in magnitude to a thin surface layer (< 30 μm) and the influence on fatigue life is comparable. In the last section, a novel prototype system is presented which allows performing the PLA repair in-situ by use of a miniaturized laser scanning head coupled with a flexible mechanical deployment arm. The system has been successfully tested inside a Roll-Royce Trent jet engine; effectively this proves the possibility of performing in-situ laser micro-machining inside complex mechanical systems such as aero-engines, without the need for complex/expensive disassembly.
关键词： Miniaturized laser system,In-situ micro-machining,Pulsed laser ablation,Aeroengines
更新于2025-09-19 17:13:59
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Enhanced visible-light-photoconversion efficiency of TiO2 nanotubes decorated by pulsed laser deposited CoNi nanoparticles
摘要： The pulsed laser deposition (PLD) technique has been used to decorate TiO2 nanotubes (NTs) with cobalt-nickel (CoNi) nanoparticles (NPs). The TiO2 NTs were produced beforehand through the controlled anodic oxidation of titanium substrates. The effect of the nature of the PLD background gas (Vacuum, O2 and He) on the microstructure, composition and chemical bondings of the CoNi-NPs deposited onto the TiO2-NTs has been investigated. We found that the PLD CoNi-NPs have a core/shell (oxide/metal) structure when deposited under vacuum, while they are fully oxidized when deposited under O2. On the other hand, by varying the CoNi-NPs loading of the TiO2-NTs (through the increase of the number of laser ablation pulses (NLP)), we have systematically studied their photocatalytic effect by means of cyclic-voltammetry (CV) measurements under both AM1.5 simulated solar light and filtered visible light. We show that depositing CoNi-NPs on the substrate under vacuum and He increases the photo-electrochemical conversion effectiveness (PCE) by 600% (at NLP = 10,000) in the visible light domain, while their overall PCE degrades with NLP under solar illumination. In contrast, the fully oxidized CoNi-NPs (deposited under O2) are found to be the most effective catalyst under sunlight with an overall increase of more than 50% of the PCE at the optimum loading around NLP ~1000. Such catalytic enhancement is believed to result from both an enhanced light absorption by CoO (of which bandgap is of ~2.4 eV) and the formation of a heterojunction between NiO/CoO nanoparticles and TiO2 nanotubes.
关键词： TiO2 nanotubes,Pulsed laser deposition,Cobalt/nickel nanoparticles,Photo-electrochemistry,Water-splitting
更新于2025-09-19 17:13:59
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Research on optimum slowly-rising driver for electro-optic Q-switched laser
摘要： Electro-optic Q-switch drivers that based on pulse transformer method have been widely used in laser engineering because of the advantages of concise circuits, low supply voltage, low lost, etc., but the long rise time and short pulse duration of the high voltage (HV) pulses have a considerable effect on the Q-switched laser outputs. In this paper, we experimentally investigated the dependence of Q-switched laser outputs on the rise rate of slowly-rising HV pulses in a flash pumped Nd:YAG laser with variable cavity lengths. LiNbO3 Q-switches with various dimensions were used. Based on the experiment results, the optimum slowly-rising HV pulses for any EO Q-switched laser were derived, the only requirement is that voltage near dynamic quarter-wave voltage during the emission of laser pulses. Additionally, the optimum outputs were found to be consistent with the results obtained by using a rapid-switching driver with a rise time of 7 ns. The optimum range of applied voltage was determined to be 0.88 – 1.12 times dynamic quarter-wave voltage.
关键词： Electro-optic Q-switching,Lithium niobate crystal,Slow rise time,Q-switch driver,Pulsed laser
更新于2025-09-19 17:13:59
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Preparation and deposition of Pr-Fe-B permanent magnet powder using pulsed laser
摘要： We have already prepared a thin permanent magnet with the thickness of sub millimeter by obtaining magnet powders using a PLD (Pulsed Laser Deposition) method. In the study, the PLD followed by a flash annealing enabled us to deposit isotropic Pr-Fe-B magnet powders with coercivity (Hcj) > 1000 kA/m on a stainless thin shaft applicable to a miniaturized motor. Observation on the surface of Pr-Fe-B magnets and evaluation on mechanical behavior was carried out. Since the surface of a Pr-Fe-B magnet was coated by a Pr oxide through an annealing process, their magnetic properties didn’t degrade after one year. We also confirmed that the Pr-Fe-B magnet has possibility to be applied to a micro magnetization process. It was clarified that the powder technology using the PLD is useful to propose a thin magnet applicable to a next generation small motor.
关键词： stainless shaft,coating,Pr-Fe-B permanent magnet powder,PLD (Pulsed Laser Deposition)
更新于2025-09-19 17:13:59