Laser-assisted Process Research Articles

Growth of hydrophilic graphene oxide layers using continuous laser ablation

Graphene oxide has attracted considerable interest due to its several different structural and electronic properties. In the present work, the feasibility of producing cost-efficient few layers graphene oxide (FLGO) by continuous-wave laser-assisted (CLA) process via heating of a graphite target is achieved. The growth of FLGO layers is tuned by varying the illumination power of the laser. In particular, it is shown that the CLA approach could be efficiently utilized to produce graphene oxide features. Micro Raman spectroscopy is used as a potent technique to confirm the formation of the FLGO layers. The D-band refers to structural disorders or defects present in the FLGO. In order to dwell into the wetting properties of these intriguing layers, water contact angle (WCA) measurements are carried out on pristine graphite and FLGO samples. It is found that the WCA properties of FLGO and graphite are in contrast with each other. The pristine graphite and water show an angle of 89°, while, FLGO, shows super-hydrophilic features. This may be attributed to the structural modification of graphite due to laser irradiation as the oxygen atoms changing their electronegativity renders GO super-hydrophilic in nature.

Site-selective synthesis of onion like carbon from nanodiamond thin film via laser-assisted photothermal process

Onion like carbon (OLC) has attracted much attention due to its promising electrochemical properties which originate from its multi sp2 carbon shells that form a spherical nanostructure with uniform size distribution. When utilized as active electrode material in electrochemical cells, it induces fast ionic diffusion and transport rates and can be used in ultrahigh powered supercapacitors. Despite the substantial promise, OLC is typically synthesized by thermal treatment of nanodiamonds (NDs) in a harsh environment (e.g., up to 1800 °C in a high vacuum), which is not feasible for direct synthesis from various substrates. Here, we propose a facile laser-induced site-selective synthesis method of OLC from ND thin film formed by a solution-based process. Spin coating of ultra-dispersed ND ink with uniform size distribution allows preparation of ND thin films of varying thickness on glass and metal substrates. Pulsed laser irradiation in a vacuum transforms the NDs into OLC in an arbitrary area, which is verified by Raman and transmission electron microscopy (TEM) analysis. The laser-synthesized OLC was employed as an active electrode in supercapacitors and demonstrated fast charge and discharge rates, hence exhibiting comparable performance to that of OLC obtained by furnace annealing. We believe that our results open an avenue to explore various electrochemical applications of OLC with designed patterns.

Formation of a Calcium Phosphate Layer with Immobilized Cobalt Chromite Nanoparticles on Cobalt−Chromium Alloy by a Laser-Assisted Biomimetic Process

The biocompatibility and osteoconductivity of metallic biomaterials can be achieved by calcium phosphate (CaP) coating. We recently developed a laser-assisted biomimetic (LAB) process for rapid and area-specific CaP coating on several materials. In the present study, the LAB process was applied to cobalt–chromium (Co−Cr) alloy, a metallic biomaterial widely used in orthopedic and dental applications. The LAB process was conducted by irradiation of unfocused pulsed laser light onto the substrate immersed in supersaturated CaP solution. The LAB-processed substrate formed CaP on the irradiated surface within only 5 min and was coated with a micron-thick CaP layer within 30 min by the effects of laser-induced surface modification and heating. Ultrastructural analysis with transmission electron microscopy revealed that the resultant CaP layer was integrated with the underlying substrate through two intermediate layers, an upper chromium oxide layer and a lower Co-rich (Cr-deficient) alloy layer. The CaP layer was loaded with a large number of cobalt chromite (CoCr2O4) nanoparticles. The results obtained offer new insights into the mechanism of CaP coating in the LAB process and future applications of LAB-processed Co−Cr alloys.

High-Speed Direct Writing of MoSe2 by Maskless and Gas-Free Laser-Assisted Selenization Process

Transition metal dichalcogenides (TMDCs) have shown exceptional optoelectronic properties that can potentially substitute conventional silicon-based devices and be utilized in sensors and energy de...

Fabrication of Chalcogenide Glass Based Hexagonal Gapless Microlens Arrays via Combining Femtosecond Laser Assist Chemical Etching and Precision Glass Molding Processes.

Chalcogenide glasses (ChGs) are emerging as critical infrared (IR)-enabled materials in advanced IR optical systems by the wealth of their transparency in the key wide infrared (IR) transmission window. However, fabrication of ChG-based integrated micro-optical components in an efficient and economical way remains a huge challenge. In this paper, a 3D close-packed hexagonal microlens array (MLA) possessing over 6000 convex hexagonal micro-lenslets with the size of tens of micrometers within a footprint of 10 mm × 10 mm on a Ge20Sb15Se65 ChG surface was successfully fabricated via a precise thermal-mechanical molding process. The master mold of ChG MLA was firstly fabricated by a femtosecond laser-assisted chemical etching process and then transferred on to the surface of the ChG via a precision thermo-mechanical molding process, which resulted in a convex MLA. The morphology, imaging and focusing performances of the as-prepared ChG MLA were investigated and demonstrated the advancement of the method. Meanwhile, the IR transmittance and x-ray diffraction image of the ChG MLAs were measured to verify the structural and compositional stability of the ChG under the given molding conditions. The combined results proved a new route to mass production of miniaturized gapless ChG MLAs for advanced infrared micro-optics.

A fully coupled local and global optical-thermal model for continuous adjacent laser-assisted tape winding process of type-IV pressure vessels

A numerical process simulation framework is introduced in this paper to describe and predict the process temperature evolution during the laser-assisted tape winding (LATW) process of a type-IV pressure vessel made of glass-reinforced high-density polyethylene (G/HDPE). A local optical-thermal model is fully coupled with a global thermal model for the simulation of continuous adjacent hoop winding cases. The predicted tape and substrate temperatures are compared with the experimental data to validate the process model’s effectiveness. The inline temperature was measured by an infrared thermographic camera during the continuous winding. The continuous process temperature of the substrate is affected significantly due to the previously wound layers including the pressure vessel, and a gradual increase of the temperature of the roller and the air inside the liner. A considerable temperature increase calculated as 80-120°C takes place for the substrate during winding of two consecutive layers of (G/HDPE) prepreg tape at the liner ends. The influence of pressure vessel size on the tape and substrate temperatures is investigated for different liner radii using the validated process model. The peak substrate temperature is found to increase approximately 45°C by reducing the radius of the pressure vessel from 272 mm to 68 mm while maintaining all other process conditions constant.

Micro-milling of 65 vol% SiCp/Al composites with a novel laser-assisted hybrid process

Micro-machining of high-volume fraction SiC particles reinforced aluminum matrix (SiCp/Al) composites is characterized by high specific cutting forces, rapid tool wear, and deteriorated surface integrity. This study presents an innovative approach of laser-induced oxidation assisted micro-milling (LOMM) to improve micro-machinability of 65 vol% SiCp/Al composites. An easy-to-remove metamorphic layer, which is composed of an oxide layer and a sub-layer, is produced when the material is treated by a nanosecond laser in an oxygen-rich environment. The oxidation mechanism of the SiCp/Al composites is investigated. Under the average laser power of 8 W, scanning speed of 1 mm/s, track displacement of 10 μm and an oxygen-rich environment, the thicknesses of the oxide layer and sub-layer are 187.3 μm and 32.5 μm, respectively. The microstructure reveals that the oxide layer is porous, which causes generation of an extremely low cutting force of 0.3 N during its removal, thus, improving the machinability. Cavities and pits are distributed on the sub-layer. The material removal mechanisms in micro-milling of SiCp/Al composites include brittle fracture of the SiC reinforcements and ductile removal of the aluminum matrix. Small cavities and fissures are formed on the machined surface. The performance of the LOMM in respect of cutting forces and machined surface quality is compared with that of conventional micro-milling. The normal and thrust forces observed in LOMM are much lower than those in conventional micro-milling. The machined surface roughness (Sa) in LOMM is 147 nm, which is far superior than 471 nm of that in conventional micro-milling. The comparative study validates the practicability and high effectiveness of the proposed hybrid process.

Square-Wave Long-Period Fiber Grating Fabricated With Double-Sided Laser-Assisted Wet Etching Technology

This study presents a square-wave double-sided long-period fiber grating sensor that was fabricated using pattern inscription by laser-assisted etching with a KrF 248-nm excimer and an aqueous solution of acid. We investigated the relationship between grating depth and the etching rate of the excimer laser-irradiated fused silica. The novelty of this sensor lies in the square-wave period grating structure created by a different etching rate on the surface of the optical fiber during the laser-assisted wet etching process and the designed period of two metal masks. We also conducted experiments that demonstrated the sensitivity of the square-wave double-sided long-period fiber grating sensor to temperature. The results showed that the average resonant wavelength/temperature ratio of the sensor was 0.054 nm/°C, while the transmission loss/temperature ratio was 0.038 dB/°C.

Role of impinging powder particles on melt pool hydrodynamics, thermal behaviour and microstructure in laser-assisted DED process: A particle-scale DEM – CFD – CA approach

High speed imaging of molten pool free-surface hydrodynamics in laser-assisted directed energy deposition process clearly revealed a highly oscillatory and dynamic melt flow due to impinging powder particles. Surprisingly, most of the reported computational work exclude the injection of powder particles and rather adopt a homogeneous mass and energy addition approach, and therefore provides less accurate predictions. In this work, we develop a coupled multi-physics particle-scale approach utilizing the discrete element method for particle trajectory prediction, the computational fluid dynamics for free-surface thermo-fluidic modelling and the cellular automata method for grain growth evolution. In the model, the governing physical phenomena, such as laser-powder interaction, in-flight particle heating, phase change (melting, vaporization and solidification), free-surface evolution, molten pool hydrodynamics and impinging particles-melt interaction have been considered. Experiments for the deposition of Inconel-625 on an Inconel-625 substrate are carried out, and the model predictions are validated with the experimental measurements. For the first time, the predicted thermo-fluidic simulation results reveal highly oscillatory, chaotic and random melt flow attributed to the impinging powder particles. During the deposition, it is found that the role of the Marangoni convection is less significant as compared to the momentum imparted by the impinging powder particles in the melt pool. Using the simulated thermal undercooling data, cellular automata-based grain growth simulation predicts elongated columnar dendrites in the melt pool that grows epitaxially from the melt pool interface and stretches towards the centre. Using the Kurz-Fisher model, the effect of local thermodynamic solidification conditions on the size of dendritic microstructure is also described. The predicted melt pool geometry, temperature field and grain structure compare well with the experimental measurements.

Laser-assisted processing of aluminum alloy for the fabrication of superhydrophobic coatings withstanding multiple degradation factors

The development of durable multifunctional coatings for materials operating in open atmospheric conditions is one of the key problems in materials science. For such coatings, the resistance to various destructive environmental factors determines the durability and efficiency of their use. In this work, using the laser processing method, a series of superhydrophobic coatings was created and the optimal processing conditions for aluminum alloys used for aircraft components were adjusted. As a result of the studies, the problems of increasing the rate of manufacturing the superhydrophobic coatings without loss of the required functional properties were solved and the properties of the obtained coatings were studied under a variety of long-term destructive factors characteristic of open atmospheric conditions. The analysis proved the possibility of significantly accelerating the manufacturing of coatings on aluminum alloys, characterized by high mechanical and chemical resistance, which increases the value of these coatings for the aviation industry.

Application of grey correlation-based EDAS method for parametric optimization of non-traditional machining processes

Higher dimensional accuracy along with better surface finish of various advanced engineering materials has turned out to be the prime desideratum for the present day manufacturing industries. To achieve this, non-traditional machining (NTM) processes have become quite popular because of their ability to produce intricate shape geometries on diverse difficult-to-machine materials. To allow these processes to operate at their fullest capability, it is often recommended to set their different input parameters at the optimal levels. Thus, in this paper, a new technique combining grey correlation method and evaluation based on distance from average solution is applied for simultaneous optimization of three NTM processes, i.e. photochemical machining process, laser-assisted jet electrochemical machining process and abrasive water jet drilling process. The derived optimal parametric combinations outperform those as identified by the other popular multi-objective optimization techniques with respect to the considered response values. The results of analysis of variance also identify the most influencing parameters for the said NTM processes. Finally, the developed surface plots would help the process engineers in investigating the effects of different NTM process parameters on the corresponding grey appraisal scores.

Laser Functionalization of Carbon Membranes for Effective Immobilization of Antimicrobial Silver Nanoparticles

Abstract Microbial contamination and biofilm formation are serious challenges in water filtration applications. Recently, carbon nanocomposite membranes with modified silver nanoparticles (AgNPs) have attracted much attention as compelling water purification membranes that can deactivate pathogenic bacteria and prevent biofilm formation. However, the effective attachment of AgNPs onto such carbon-based surfaces has proven difficult to accomplish via inexpensive and rapid fabrication processes. In this study, we introduce a simple laser-assisted process that enables rapid surface functionalization and immobilization of AgNPs onto carbon cloth membrane surfaces comprised of woven carbon micro fibers. The laser functionalization provides a unique modification in surface morphology of the fibers by creating nanotextures as well as inducing changes in surface chemistry, all of which increase the physical and chemical bonding of AgNPs onto the surface of carbon fibers. Elemental and surface morphology analysis via XRD, SEM, and EDX reveal a uniform coating and strong attachment of AgNPs onto the laser functionalized carbon surface, even after vigorous mechanical agitations and probe sonication. The analysis showed the samples prepared by the laser functionalization prior to AgNPs coating provided exceptional antibacterial activity and ability to completely eradicate the bacteria within 4 h and resist biofilm formation against pathogenic bacterial strains of Escherichia coli. The developed technology provides new opportunities to develop a scalable, fast, and cost-effective preparation method for producing carbon-based materials/membranes with high antimicrobial activities which can be applied for water purification and other environmental applications.

Effects of calcium-phosphate, laser and adhesive on dentin permeability and bond strength

ObjectivesThe present study examined a technique for reducing dentin permeability through the application of a calcium phosphate (CaP)-based desensitiser with a laser-assisted process and evaluated adhesive-dentin bond strength. Methods: Thirty dentin discs were divided into two groups according to whether the selected desensitiser (TeethMate; Kuraray Noritake) was used prior to dentin bonding. Each group was subdivided into three subgroups (n = 5): A- Adhesive (Single Bond Universal, 3M ESPE), AL- Adhesive + Laser (Nd:YAG 60 mJ) and LAL- Laser + Adhesive + Laser. Dentin permeability values (%) were recorded before and after desensitiser application. Resin composites were placed over the bonded specimens; the latter were aged prior to microtensile bond strength evaluation. Gelatinolytic activity within the hybrid layers was examined with in-situ zymography using confocal laser scanning microscopy. Data were analysed with ANOVA and Tukey test (α = 0.05). ResultsSignificant differences in dentin permeability were identified for all groups (p = 0.00). Both laser treatment (p = 0.182) and desensitiser application (p = 0.687) did not significantly improve dentin bond strength. Ultrastructure of the resin-dentin interface identified presence of calcium phosphate within dentinal tubules. Laser treatment did not affect hybrid layer ultrastructure. Both treatment modalities (intratubular CaP occlusion and laser) had no influence on gelatinolytic activity within hybrid layers. ConclusionAlthough intratubular CaP occlusion and laser treatment were effective in reducing dentin permeability, they did not affect bond strength, interfacial ultrastructure and gelatinolytic activity within hybrid layers. Clinical relevanceTreatment of etched dentin with Nd:YAG Laser at 60 mJ does not adversely affect collagen ultrastructure and gelatinolytic activity within the hybrid layer. The application of a calcium phosphate-based desensitiser to etch dentin does not affect dentin bond strength.

Fuzzy decision-making in laser-assisted joining of polymer-metal hybrid structures

A fuzzy decision-making approach was developed to optimize laser-assisted joining process of polymer-metal hybrid structures. A systematic approach based on Design of Experiment was adopted to identify and explain the effect of each process parameter, i.e. laser energy and laser power, on the response variables, i.e. maximum operating temperature and shear strength. Then, a combined fuzzy-genetic algorithm model was developed to find the best input parameters’ combination capable to satisfy the requirement of the best processing performances, in terms of appropriate range of operating temperature and highest shear strength. The use of genetic algorithms involved the choice of the best nominal regression model and the optimisation of the fuzzy numbers. This enabled to account most of the experimental data in combination with the smallest uncertainty level. Experimental results showed the success of the joining process ensuring sufficient adhesion of the hybrid structure over time, with shear strength of almost 29 MPa by using a laser power of 150 W and energy of 2 kJ. Moreover, the fuzzy process maps enable the selection of the process parameters with the aim of achieving desired process output along with the lowest uncertainty level. In addition, it also provides the amount of uncertainty of the model. The results indicated that a low laser energy level of 2250 J and a laser power in the range 120–140 W would provide the optimal solution in terms of operating temperature (i.e. between 343 and 520 °C), shear strength (i.e. greater than 26 MPa) and uncertainty level (i.e. membership level greater than 0.9).

Laser-assisted embedding of all-glass optical fiber sensors into bulk ceramics for high-temperature applications

We develop a laser-assisted sensor embedding process to embed all-glass optical fiber sensors into bulk ceramics for high-temperature applications. A specially designed two-step microchannel was fabricated on an Al2O3 substrate for sensor embedment using a picosecond (ps) laser. An optical fiber Intrinsic Fabry-Perot Interferometer (IFPI) sensor was embedded at the bottom of the microchannel and covered by Al2O3 slurry which was subsequently sintered by a CO2 laser. The sensor spectrum was in-situ monitored during the laser sintering process to ensure the survival of the sensor and optimize the laser sintering parameters. By testing in furnace through high temperature, the embedded optical fiber shows improved stability after CO2 laser sealing, resulting in the linear temperature response of the embedded optical fiber IFPI sensor. To improve the embedded IFPI sensor for thermal strain measurement, a dummy fiber was co-embedded with the sensing fiber to improve the mechanical bonding between the sensing fiber and the ceramic substrate so that the thermal strain of the ceramic substrate can apply on the sensing fiber. The response sensitivity, measurement repeatability and high-temperature long-term stability of the embedded optical fiber IFPI sensor were evaluated in this work.

The enhancement of excitonic emission crossing Saha equilibrium in trap passivated CH3NH3PbBr3 perovskite

Metal-halide semiconductor perovskites have received great attention for the development of stable and efficient light emitting diodes and lasers, since they combine high charge carrier mobility and light emission spectral-purity with low-cost fabrication methods. Nevertheless, the role of excitons, free carries and trap states in perovskite light emission properties is still unclear due to their interdependence. In this paper we selectively manage trapping and light emission mechanisms by a reversible laser-assisted trap-passivation process performed on a CH3NH3PbBr3 perovskite layer, coupled to the inner modes of a high-quality micro-cavity, which only affects the radiative recombination. We show that photoluminescence is dominated by exciton radiative decay process and that trap states passivation increases the exciton gemination rate by reducing coulombic scattering of free electrons due to the ionized impurities. This picture provides a more general description than the model based on trap states-free Saha thermodynamic equilibrium between photo-generated species.

Experimental investigation on CO2 laser-assisted micro-slot milling characteristics of borosilicate glass

Demands for micro-machining on glass have been increasing in various industries due to the unique properties of glass, such as transparency or biocompatibility. However, micro-channel fabrication on glass with high precision has been challenging due to its brittle characteristics. This research presents the CO2 laser-assisted micro-milling process and investigates the machining characteristics experimentally. Micro-channels without cracks were fabricated using micro-end mill and CO2 laser irradiation as an assisting heat source. Compared to the process without laser heating in the same matching conditions, the average surface roughness was reduced by 96%, and cutting force was reduced by 28% and 66% for the feed and thrust direction, respectively. Continuous and sheared chips were observed with laser heating, indicating the process is in ductile-regime machining. Through the investigation of machining parameters, it was found that micro-channels with low average surface roughness can be achieved at the proper laser power when the workpiece is heated up to the strain point at tool position, at low feed rate, and at high axial depth of cut, as long as the tool withstands the cutting forces. Consequently, it can be concluded that it is possible to increase the material removal rate in micro-milling of borosilicate glass with high quality by using the CO2 laser, which was found to be an effective and suitable heating method.

Springback control in laser-assisted bending manufacturing process by using a fuzzy uncertain model

This study wants to propose a fuzzy model able to describe the inherent uncertainties related to a laser-assisted bending process and it is aimed at controlling of the springback phenomena, for a different set of laser process parameters. The process maps obtained are used to select the operational parameters in order to obtain the desired process output, providing as additional information how much the uncertainty of the model and the process varies by changing those operational parameters. The fuzzy model has also been used to assess the optimal parameters in order to satisfy the requirement of the least-cost.

Structural Analysis of Calcium Phosphate-Based Submicrospheres with Internally-Crystallized Iron Oxide Nanoparticles Fabricated by a Laser-Assisted Precipitation Process.

Calcium phosphate (CaP)-based submicrospheres containing magnetic iron oxide (IO) nanoparticles (IO–CaP submicrospheres) have potential for various biomedical applications. We recently achieved facile one-pot fabrication of IO–CaP submicrospheres using a laser-assisted precipitation process in which weak pulsed laser irradiation was applied to a labile CaP reaction mixture supplemented with ferrous ions under adequate pH. In this study, we performed cross-sectional transmission electron microscopy (TEM) analysis of the resulting IO–CaP submicrospheres. The cross-sectional TEM analysis revealed that the IO–CaP submicrospheres were heterogeneous in their internal nanostructures and could be categorized into two types, namely types A and B. The type A submicrospheres contained single nano-sized IO nanoparticles homogeneously dispersed throughout the CaP-based matrix. The type B submicrospheres contained larger IO nanoparticles with an irregular or spherical shape, which were mostly a few tens of nanometers in size along with one or two submicron-sized domains. These findings provide new insight into the formation mechanism of IO–CaP submicrospheres in this fabrication technique as well as future applications of the resulting IO–CaP submicrospheres.

Resonant photoproduction of high-energy electron-positron pairs in the field of a nucleus and a weak electromagnetic wave

The resonant photoproduction of ultrarelativistic electron-positron pairs (PPP) in a nuclear field and a weak laser field is theoretically studied. Under resonance conditions, the intermediate virtual electron (positron) in the laser field becomes a real particle. As a result, the initial process of the second order in the fine structure constant in the laser field effectively reduces into two successive processes of the first order: single-photon production of electron-positron pair in a laser field (laser-stimulated Breit-Wheeler process) and laser-assisted process of electron (positron) scattering on a nucleus. Resonant kinematics of PPP is studied in details. It is shown that for the considered laser intensities resonance is possible only for the initial photon energies greater than the characteristic threshold energy. At the same time, the ultrarelativistic electron and positron propagate in a narrow cone along the direction of the initial photon momentum. The resonant energy of the positron (electron) can has two values for each radiation angle which varies from zero to some maximum value determined by the energy of the initial photon and the threshold energy. Resonant differential cross section of the studied process was obtained. It is shown that the resonant differential cross section of the PPP can significantly exceed the corresponding cross section of the PPP without an external field. The project calculations may be experimentally verified by the scientific facilities of pulsed laser radiation (SLAC, FAIR, XFEL, ELI, XCELS)