Laser Beam Irradiation Research Articles

ショットライニングとレーザ照射によるアルミニウム合金の表面改質

The surface modification of aluminum alloy by shot lining and laser irradiation was investigated to form a hard Fe-Al intermetallic compound having excellent corrosion resistance. A centrifugal-type peening machine with an electrical heater was employed. The shot medium was high-carbon cast steel. The substrate was a commercial aluminum alloy. The sheet was commercially available pure aluminum, and the powder was an electrolytic iron. The shot lining process was carried out at 573 K in air using a peening machine. The top surface of the lined workpiece was melted by laser beam irradiation. The intermetallic Fe-Al layer was formed on the irradiated surface. The lined substrates exhibited a harder layer of aluminum-rich intermetallic in the irradiated part. The present method could be used for the formation of functional films on aluminum alloy.

Two-Beam Ultrafast Laser Scribing of Graphene Patterns with 90-nm Subdiffraction Feature Size

The fabrication of high-resolution laser-scribed graphene devices is crucial to achieving large surface areas and thus performance breakthroughs. However, since the investigation mainly focuses on the laser-induced reduction of graphene oxide, the single-beam scribing provides a tremendous challenge to realizing subdiffraction features of graphene patterns. Here, we present an innovative 2-beam laser scribing pathway for the fabrication of subdiffraction graphene patterns. First, an oxidation reaction of highly reduced graphene oxide can be controllably driven by irradiation of a 532-nm femtosecond laser beam. Based on the oxidation mechanism, a 2-beam laser scribing was performed on graphene oxide thin films, in which a doughnut-shaped 375-nm beam reduces graphene oxide and a spherical 532-nm ultrafast beam induces the oxidation of laser-reduced graphene oxide. The spherical beam turns the highly reduced graphene oxide (reduced by the doughnut-shaped beam) to an oxidized state, splitting the laser-scribed graphene oxide line into 2 subdiffraction featured segments and thus forming a laser-scribed graphene/oxidized laser-scribed graphene/laser-scribed graphene line. Through the adjustment of the oxidation beam power, the minimum linewidth of laser-scribed graphene was measured to be 90 nm. Next, we fabricated patterned supercapacitor electrodes containing parallel laser-scribed graphene lines with subdiffraction widths and spacings. An outstanding gravimetric capacitance of 308 F/g, which is substantially higher than those of reported graphene-based supercapacitors, has been delivered. The results offer a broadly accessible strategy for the fabrication of high-performance graphene-based devices including high-capacity energy storage, high-resolution holograms, high-sensitivity sensors, triboelectric nanogenerators with high power densities, and artificial intelligence devices with high neuron densities.

Modeling optical emission from a highly multi-mode step-index fiber via ray tracing and the limitations.

Geometric optics is widely applied for diverse optical simulations. In this work, we introduce an incoherent ray model to describe the laser beam radiation emitted from a highly multi-mode step-index fiber, which is frequently applied for industrial laser material processing. First the mathematical validation and the limitation of this model are demonstrated. Then we determine the ray density and the angular spectrum according to measured intensity profiles along the caustic. Furthermore, based on the determined information, we demonstrate the simulation and measurement of the laser beam shaped by an axicon telescope. Not only the reconstruction itself, but also the simulation with free form optics present significant agreements to the measurements. The reasonable modeling of a laser source via geometric optics enables the precise determination of laser radiation and propagation properties with refractive beam shaping technologies.

Unconventional Approaches to Light-Promoted Dynamic Surface Morphing on Polymer Films

Abstract Recent progress in research of light-promoted surface morphing on polymer materials is reviewed. Photoinduced mass transport motions in azobenzene polymers leading to surface relief gratings (widely called SRGs) formation are well-known and extensively discussed. Among many efforts, this article focuses on unconventional approaches, most of which are seemingly less highlighted. The first part introduces investigations using azobenzene polymers; introducing supramolecular approaches with tunable and removable azobenzene units, self-structuring of surface morphology upon single laser beam irradiation, photo-triggered migration via Marangoni flow, SRG formation and other functions of polymer brushes etc. The second part overviews the mass transport motions driven by other photoreaction classes such as photopolymerization, photocrosslinking, and photoisomerization of non-azobenzene components. The final part describes new dynamic surface morphing processes observed in fingerprint texture of liquid crystals and liquid crystal polymer networks, which can be applied to reversible friction control and self-cleaning. These uncommon attempts at photo-assisted dynamic morphing extend the possibilities of microfabrication on polymer films and are expected to find new opportunities to create new surface functions in soft materials.

Laser synthesis of a weakly agglomerated aluminium oxide nanopowder doped with terbium and ytterbium

This paper describes a method of femtosecond laser synthesis of nanoparticles of powdered aluminum oxide doped with terbium and ytterbium was developed. The formation of a plasma torch of nanoparticles of a powdery material is carried out as a result of ablation under the influence of a sharply focused beam of femtosecond laser radiation with an intensity of 108- 1010W/m2. The radiation source is the TETA-10 laser system. SEM images of the obtained nanopowders are presented. Spherical nanoparticles of narrow particle size distribution in the range from 5 to 15 nm was synthesized with the ability to control the size of nanoparticles by purposefully changing the parameters and characteristics of pulsed radiation in the treatment area. The design of a specialized high-voltage electrostatic precipitator up to 25 kV for capturing ablated nanoparticles in an electron cloud of increased concentration was developed.

Fabrication of Release Agent Supply Die with Porous Structure Using Metal-Based Additive Manufacturing

In powder bed fusion (PBF), a type of metal-based additive manufacturing (AM) process, metal powders are deposited on a substrate and melted through selective laser-beam irradiation. Among AM processes, PBF yields excellent dimensional accuracy, and the built parts can be applied to molding dies and topology-optimized parts. Furthermore, PBF can be used to build porous structures. In this study, a highly functional die casting method was established using PBF, which involved a release agent supplied through the porous structure to the surface of the proposed die. The arrangement of the porous structure made it possible to apply the release agent to the deep groove, which is not possible using a spray as in conventional supply methods. The laser-irradiated area was visualized to confirm pore formation, and the building conditions of the porous structure suitable to supply the release agent were investigated. The resulting die casting characteristics were evaluated. Considering the obtained results, guidelines to build dies or molds for die casting with porous structures are recommended. The amount of release agent could be controlled at each position of the die casting die, and the melted Al alloy did not penetrate the porous structure. In addition, the obtained Al alloy casting did not exhibit any castability defects. Moreover, suitable control of the supply of the release agent enabled enhancement of the die casting characteristics.

Modification of Tin (Sn) metal surfaces by surface plasmon polariton excitation

We report on the modification of tin (Sn) film surfaces under a laser beam irradiation that triggers surface plasmon polariton (SPP) excitations. The observed surface features in the form of small raised grains, with well-defined rooting, look similar to tin whisker nodules. We attribute the appearance of those features to the field-induced nucleation caused by the SPP related strong electric field. Possible implications of our findings include accelerated-life testing for tin whisker growth related reliability as well as applications to nanoparticle nucleation.

Fast Welding of Silver Nanowires for Flexible Transparent Conductive Film by Spatial Light Modulated Femtosecond Laser

Silver nanowires (AgNWs) conductors with fine flexibility and high conductivity have been considered to have a promising perspective in the area of flexible transparent electrode. However, many challenges still exist in improving the conductivity of AgNWs films, such as high temperature and time‐consuming. Herein, an efficient and rapid method to weld AgNWs by spatial light modulated femtosecond (fs) laser is proposed. The Gaussian laser beam is modulated into a line‐shaped laser beam with the length of 773 μm. Compared with traditional spherical lens focus irradiation welding, the welding efficiency can be improved up to tens of times. The mechanism of fs laser welding is mainly to use high‐energy laser beam irradiation to generate local field enhancement which causes local high temperature at the nanowire junction. After laser welding, the sheet resistance of AgNWs films can be reduced to 14.7 Ω sq−1 at the transmittance of 89.5% without substrate damage. The welded AgNWs films exhibit excellent electrical conductivity even after 10 000 bending cycles. Moreover, the welded AgNWs films are used to make a flexible transparent heater, showing superior sheet resistance uniformity.

Experimental Investigation of the Effects of Irradiating Schemes in Laser Tube Bending Process

The laser tube bending process (LTBP) process is a thermal non-contact process for bending tubes with less springback and less thinning of the tube. In this paper, the laser tube bending process will be studied experimentally. The length of irradiation and irradiation scheme are two main affecting process parameters in the LTBP process. For this purpose, different samples according to two main irradiation schemes (Circular irradiating scheme (CIS) and axial irradiating scheme (AIS)) and different lengths of laser beam irradiation (from 4.7 to 28.2 mm) are fabricated. The main bending angle of laser-bent tube, lateral bending angle, ovality, and thickness variations is measured experimentally, and the effects of the irradiating scheme and the length of irradiation are investigated. An 18 mm diameter, 1 mm thick mild steel tube was bent with 1100 Watts laser beam. The results show that for both irradiating schemes, by increasing the irradiating length of the main and lateral bending angle, the ovality and thickness variation ratio of the bent tube are increased. In addition, for a similar irradiating length, the main bending angle with AIS is considerably higher than CIS. The lateral bending angle by AIS is much less than the lateral bending angle with CIS. The results demonstrate that the ovality percentage and the thickness variation ratio for the laser-bent tube obtained by CIS are much more than the values associated with by AIS laser-bent tube.

Conformable metal oxide platelets – A smart surface armor for green tribology

The reduction of friction and wear is a crucial performance criterion for most technical processes. This is particularly true for the ubiquitous case of oil lubricated machinery made from steel components. Here we introduce a facile laser treatment that significantly enhances the tribological performance of bearing steel 100Cr6, a material widely used for the manufacture of ball and roller bearings. By applying repeated nanosecond-pulses of focussed laser-beam irradiation under ambient air, a surface-protective tribo-layer is generated by a method that exploits self-organization for the formation of conformable metal oxide platelets consisting of vertically aligned transition metal oxides nanorods on the steel substrate. These submicron-sized metal oxide platelets protect the surfaces similar to scale armor and the tribological performance of the bearing steel 100Cr6 was significantly enhanced. Based on laboratory tests using a rotational pin-on-disk tribometer under oil lubricated conditions, close to zero wear with simultaneous reduction of friction by 54% was achieved. Even under the harsh conditions in the pin-on-disk tribometer these metal oxide platelets turn out to be remarkably robust against detachment and crumbling for lasting millions of cycles at a slip rate of 100%. The origin of this resilience is based on a special substructure of the platelets that, counter-intuitively for ceramic material, enables shape adaptations to surface deformations emergent upon high mechanical stress.

Thermal stress cleavage of a single-crystal round sapphire bar by carbon dioxide laser

This study is the first attempt of applying thermal stress cleavage to a single-crystal round sapphire bar having a morphologically continuous circumference surface. Previously, thermal stress cleavage was only applied to brittle material substrates or wafers owing to the crack propagation behaviour induced by thermal stress distribution. To overcome this issue, a V-shaped groove was prepared on the circumference as an initial point for crack propagation, and a continuous-wave carbon dioxide (CO2) laser was used as the heat source. The thermal stress behaviour was simulated via finite element analysis, and the effect of the initial crack morphology on the thermal stress behaviour was evaluated. In addition, the crack propagation was monitored using an acoustic emission sensor, and the separation mechanism of the round sapphire bar was investigated. Results indicated that the thermal stress cleavage using the CO2 laser beam allowed the complete separation of the round sapphire bar with the V-shaped groove without any final edge remaining. The crack propagation behaviour was determined from the relationship between the thermal stress distribution and morphology change during crack propagation. The fabricated sharp V-shaped groove improved the quality of the cleaved surface, and the high aspect ratio of the groove enabled a high-quality cleavage. The initial crack propagation immediately after the start of laser beam irradiation was affected by the tip of the V-shaped groove, and the crack propagation direction could be controlled through the tip morphology of the V-shaped groove.

Behavior of rat bone marrow stem cells on titanium surfaces modified by laser-beam and deposition of calcium phosphate

ObjectivesThe aim of this study was to evaluate the behavior of rat bone marrow stem cells seeded on a Ti-15Mo alloy surface modified by laser-beam irradiation followed by calcium phosphate deposition.Materials and methodsA total of four groups were evaluated: polished commercially pure titanium (cpTi): Ti-P; laser irradiation + calcium phosphate deposition on cpTi: Ti-LCP; polished Ti-15Mo alloy: Ti15Mo-P; and laser irradiation + calcium phosphate deposition on Ti-15Mo alloy: Ti15Mo-LCP. Before and after laser irradiation and calcium phosphate deposition on the surfaces, physicochemical and morphological analyses were performed: Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDX). The wettability of the samples was evaluated by contact angle measurement. In addition, the behavior of osteoblast-like cells to these surfaces was evaluated for cell morphology, adhesion, proliferation and viability, evaluation of alkaline phosphatase formation and gene expression of osteogenesis markers.ResultsSurfaces wet-abrade with grit paper (P) showed oriented groves, while the laser irradiation and calcium phosphate deposition (LCP) produced porosity on both cpTi and Ti15Mo alloy groups with deposits of hydroxyapatite (HA) crystals (SEM). EDX showed no contamination after surface modification in both metal samples. A complete wetting was observed for both LCP groups, whereas P surfaces exhibited high degree of hydrophobicity. There was a statistical difference in the intragroup comparison of proliferation and viability (p < 0.05). The ALP activity showed higher values in the Ti15Mo alloy at 10 days of culture. The gene expression of bone related molecules did not present significant differences at 7 and 14 days among different metals and surface treatments.ConclusionTi15-Mo seems to be an alternative alloy to cpTi for dental implants. Surface treatment by laser irradiation followed by phosphate deposition seems to positively interact with bone cells.Clinical relevanceTi-15Mo alloy surface modified by laser-beam irradiation followed by calcium phosphate deposition may improve and accelerate the osseointegration process of dental implants.

Molecular reorientation behavior of oligothiophene-doped polymer-stabilized liquid crystals irradiated with collimated laser beam

The irradiation of oligothiophene-doped liquid crystals (LCs) with a linearly polarized laser beam induces homeotropic-to-planar director reorientation. However, such molecular reorientation was explored only with a focused laser beam, which requires a lens and consequently limits their application. We report photoinduced molecular reorientation behavior of oligothiophene-doped LCs by irradiation with a collimated laser beam. We prepared the homeotropic aligned oligothiophene-doped LC and irradiated the sample with collimated and focused laser beams. As a result, the irradiation with a collimated beam induced molecular reorientation of LCs and its threshold intensity became lower than that of focused laser beam irradiation.

Explosions, Powerful Shock Waves, and Extreme States of Matter

Extreme states arise when a substance is exposed to powerful shock, detonation and electric explosive waves, concentrated laser radiation, electron and ion beams, during powerful chemical and nuclear explosions, hypersonic motion of bodies in dense planetary atmospheres, high-speed impact, and in many other situations characterized by extremely high pressures and temperatures. The study of matter under extreme conditions is one of the most urgent and intensively developing fundamental scientific disciplines, located at the intersection of plasma physics, nonlinear optics, condensed state, nuclear, atomic and molecular physics, and relativistic and magnetic hydrodynamics. In our country, research in the field of physics of high energy density and extreme states of matter is dynamically developing thanks to the active cooperation of the Russian Academy of Sciences and the Rosatom State Atomic Energy Corporation.

A comparing study of defect generation in IN738LC superalloy fabricated by laser powder bed fusion: Continuous-wave mode versus pulsed-wave mode

Inconel 738 LC samples were fabricated using laser powder bed fusion under continuous-wave and pulsed-wave modes. Microstructure, surface quality and mechanical properties were compared to evaluate the printing quality between these 2 laser beam modes. The results show that the application of pulsed wave could effectively eliminate cracking in the as-fabricated sample, despite 0.046% porosity generated. Further microstructure analysis revealed that the refinement of grains by the pulsed-wave laser beam was the main contributor in eliminating the cracks. And this refinement was ascribed to the higher cooling rate under the discontinuous radiation of laser beam proofed by the numerical simulation. And the pore formation was related to Rayleigh instability and residual bubbles in the sample under the pulsed-wave mode, while pores were less detrimental to the mechanical properties than cracks. Therefore, the part under the pulsed-wave mode exhibited superior mechanical performance compared to that under the continuous-wave mode.

Nanosecond and sub-nanosecond laser-assisted microscribing of Cu thin films in a salt solution

Pulsed laser-based material removal is a preferred technique for microscribing of copper (Cu) film coated on polymers, as the pulse width limits the heat diffusion. However, experimental studies have shown that microscribing of Cu in air results in recast/redeposit formation and oxidation. Although the water medium can reduce these effects to a certain extent, the material removal rate is lesser for Cu. This article reports the influence of laser pulse duration on a hybrid method to enhance the pulsed laser-assisted microscribing of a copper thin film in the presence of an environmentally friendly sodium chloride salt solution (NaCl). The focused laser beam irradiation of Cu film results in ablation with a temperature of the zone well above the boiling point of Cu, which in turn, can assist in accelerating the chemical reaction. In this hybrid scribing technique, along with laser-based material removal, laser-activated chemical etching also helps in removing the material selectively. A sub-nanosecond laser with a pulse width of 500 ps (picosecond [ps] laser) and a nanosecond laser with a pulse width of 6 ns (nanosecond [ns] laser), with a wavelength of 532 nm, are used to understand the influence of laser pulse duration on this hybrid material removal mechanism. Hybrid microscribing with the ps- and ns lasers in salt solution resulted in an increase in the channel depth by ≈5 µm and ≈9 µm, respectively, compared to the channel depth obtained in deionized water. The theoretical model shows that during the ns laser ablation, the cooling rate is slower, resulting in a high temperature in the ablation zone for a longer duration and improved material removal.

Simulated and experimental analysis of laser beam energy profiles to improve efficiency in wire-fed laser deposition

Laser cladding is a well-established technique, with the majority of prior numerical modelling work focused on delivery and melt pool behaviour of powder-based processes. This research presents new investigations into optimised laser beam shaping for the unique characteristics of wire-based processes, where direct substrate heating, as well as heat transfer between the wire and substrate, is important. The value of this subject is the improved deposition rates and dense metallic structures that can be achieved by wire-based deposition processes compared to powder-based material delivery. The within-wire temperature distribution (AISI 316 stainless steel), the heat transfer and direct heating of the substrate (mild steel) are modelled via heat transfer simulations, with three laser beam irradiance distributions. This analysis identified the removal of localised high-temperature regions typically associated to standard Gaussian distributions, and the improved substrate heating that a uniform square beam profile can provide. Experiments using pre-placed wire and a 1.2 kW CO2 laser were analysed using cross-sectional optical microscopy to provide model validation and evidence of improved wire-substrate wetting, while maintaining favourable austenitic metallurgy in the clad material. A key finding of this work is a reduction, from 480 to 190 W/mm2, in the required irradiance for effective melt pool formation when changing from a Gaussian distribution to a uniform square distribution. This also provided a 50% reduction in total energy. The potential improvements to energy efficiency, cost reductions and sustainability improvements are recognised and discussed.

Investigation on millijoule femtosecond laser spiral drilling of micro-deep holes in thermal barrier coated alloys

Ultra-short laser drilling of micro-holes with high quality and high processing efficiency in the aviation industry is urgently needed. This study reported the fabrication of micro-deep holes on thermal barrier coated alloys through millijoule femtosecond laser beam irradiation. The self-focusing effect (Kerr effect induced by the intense beam itself) and waveguide effect (reflections induced by the sidewall) on beam propagation behavior inside the micro-deep hole were investigated. The experimental results showed the number of spiral orbits required for through holes has little change within a certain defocus range. Combined with the simulation analyses, it reveals that self-focusing can reinforce the laser intensity in the deep of micro-holes, preventing the beam energy attenuation as the depth of hole increases. Additionally, the guidance and reflection of the sidewall will also make the beam self-converge and enhance its intensity. The enhancement of the laser intensity in the hole cavity can help shorten the processing time. Furthermore, as the aperture increases, the self-focusing still has the noteworthy effect on the intensity enhancement inside the cavity, while the waveguide effect of the sidewall on the intensity enhancement will be weakened. The section profile of holes was analyzed, delamination-free was achieved, and no recast layer was found.

Numerical Simulation and Verification of Laser-Polishing Free Surface of S136D Die Steel

As a novel polishing technology, polishing by laser beam radiation can be used to improve the sample surface finish without causing material losses. In order to study the effect of laser polishing on the surface morphology of S136D die steel, an L16(44) orthogonal experiment was designed to describe the variation trend of surface roughness with energy density. The two-dimensional transient model of laser polishing was established to simulate the evolution process of material surface morphology during laser polishing by combining numerical simulation with the experiment. The model uses a moving laser heat source to study the effects of capillary pressure and thermocapillary pressure in the laser polishing process. The experimental results show that the minimum roughness can be reduced to 0.764 μm, and the error between the actual molten pool depth and the simulated molten pool depth is 5.3%.

Using Toulmin’s Argument Pattern Approach to Identify Infodemics in the Covid-19 Pandemic Era

The emergence of various web pages and social media platforms that exist in today’s digital information era makes it easy for us to access various sources of information and makes us flooded with information. This condition has the potential to result in the loss of our mental health. This is known by the World Health Organization (WHO) as an infodemic which is an excessive amount of information, both true and false, which makes it very difficult for people to find reliable news about the coronavirus, and has increased the spread of fake news, conspiracy theories, worldwide panic and confusion. WHO and all the governments of each country in the world have also carried out various efforts to break the chain of spreading fake news. But the spread of fake news around the world is faster than there is any control over it. Therefore, we need an awareness of each individual in order to equip themselves with the knowledge and skills in identifying fake news. Physics as a branch of science discipline cannot be separated from this fake news. One example of fake news about physics related to Covid-19 is the statement that the thermo gun used to measure body temperature is dangerous to human health because of its laser beam radiation. One alternative way that can be used to evaluate the truth of the news is by assessing the strength of the news argumentation. Toulmin’s argument pattern has been widely applied to analyze the quality of an argument, which can be applied in evaluating the truth of a received news content. This paper aims to provide an alternative in identifying the “infodemic” in the Covid-19 Pandemic era in evaluating the correctness of information by applying the Toulmin Argument Pattern. This argumentation pattern distinguishes three fundamental components and three additional components of a coherent argumentative discourse. The main framework of this pattern in analyzing arguments consists of three main components: claim, data, and warrant. Where data provides the basis for determining claims, warrant acts as a logical reasoning bridge that connects data and claims. Three additional components can be added to construct a more complex pattern for analyzing arguments: backings, qualifiers, and rebuttals. Where backing is the part that provides additional evidence to strengthen the warrant, Qualifiers indicate the strength provided by the warrant in relating data to claims, while rebuttals indicate circumstances where the warrant in this condition is no longer valid so that the claim can be rejected.