Multiple Laser Scanners Research Articles

Diamond coatings on copper surfaces through interface engineering

To address the challenges posed by the significant thermal stress and limited affinity of diamond coatings on copper (Cu) substrates, we developed a method combining femtosecond (fs) laser texturing with the application of a nickel (Ni) interlayer. This technique was utilized for adhesion enhancement of diamond coatings on Cu. By varying the deposition duration and microgrid depth through multiple fs laser scanning passes, it is possible to attain well-adhered diamond coatings on Cu substrates. These coatings demonstrate an outstanding quality factor of 93.4% and an average grain size of 5.5 μm. The enhanced adhesion results from the synergistic reinforcement of the mechanical interlock and anchoring mechanisms facilitated by the textured surface, further bolstered by the presence of the Ni interlayer. Moreover, the shape of the texture significantly influences the deposition outcome. Single-crystal diamonds with an average grain size of 10 μm were achieved on sharp microgrids at a substrate temperature of 550 °C. This work is expected to offer a general approach for deposition of diamond coatings on metallic materials with enhanced adhesion.

Microstructure Tailoring for High Strength Ti-6Al-4V without Alloying Elements through Optimized Preheating and Post-Heating Laser Scanning in Laser Powder Bed Fusion

Ti-6Al-4V with its eclectic array of excellent properties along with the combination of meticulous precision and flexibility offered by the laser powder bed fusion (LPBF) technology makes it a strong proponent in the field of engineering applications. As a substantial amount of research has paved the way to fabricate Ti-6AL-4V more effectively and efficiently, researchers are becoming more adventurous in finding out the optimal techniques to get better yields in terms of mechanical responses. This includes post-processing techniques i.e., heat treatment (HT) or introducing various alloying elements. Nevertheless, these techniques not only make the overall fabrication more expensive and time-consuming but also contradict the simplistic notion of additive manufacturing (AM) by imparting multistage fabrication without a considerable improvement overall. Here, we propose an innovative breakthrough in the field of Ti-6AL-4V fabrication with LPBF by introducing an in-situ approach to tackle the handicap mentioned in contemporary studies. By imparting multiple laser scans prior to and after the melting scan at each layer, a remarkable 37% improvement in yield strength (YS) can be achieved with higher elongation, while also maintaining a high relative density of around 99.99%.

Effects of Laser Scanning Strategy on Bending Behavior and Microstructure of DP980 Steel

Laser bending is a kind of cumulative forming technology and bending efficiency is one of its most important indexes. This study investigates the bending behavior and the microstructure of DP980 steel plates under different laser scanning strategies, using an IPG laser system. Two sets of experiments varied the accumulated line energy density (AED) by altering the laser scanning velocity and number of scans. The results show that, for the single laser scanning process, the bending angle of the plate increases with AED, due to a larger temperature gradient through the thickness direction; however, this relationship is nonlinear. A higher AED led to a sharper initial increase in bending angle, which then plateaued. Under the same AED conditions, the bending angle of the plate undergoing multiple laser scans increases by at least 26% compared to the single one, due to the microstructure changes. It is revealed that the bending efficiency is affected by both the AED and the resultant microstructure evolution in the DP980 steel. Higher AED values and appropriate peak temperatures facilitate better bending behavior due to the formation of uniform martensite and grain refinement. Conversely, excessive peak temperatures can hinder bending due to grain growth.

EBSD investigation of microstructure and microtexture evolution on additively manufactured TiC-Fe based cermets—Influence of multiple laser scanning

Sustainable TiC-Fe-based cermets have been fabricated by adopting an Additive Manufacturing route based on laser powder bed fusion technology (L-PBF). The objective is to produce crack-free cermet components by employing novel multiple laser scanning techniques with variations in laser process parameters. Electron backscatter diffraction analysis (EBSD) was used to study the microstructure and microtexture evolution with variations in laser process parameters. The investigation revealed that adjusting the preheating scan speed (PHS) and melting scan speed (MS) influenced the growth and nucleation of TiC phases. Lowering these speeds resulted in grain coarsening, while higher scan speeds led to grain refinement with larger sub-grain boundaries. Moreover, a high scanning speed increases the degree of dislocation density and internal stress in the fabricated cermet parts. Notably, it is revealed that decreasing the laser scan speed enhanced the proportion of high-angle grain boundaries in the cermet components, signifying an increase in material ductility.

Performance and mechanisms of ultraviolet laser ablation of plain-woven CFRP composites

Plain-woven carbon-fiber-reinforced-polymer (CFRP) composites prove advantageous in designing and manufacturing aeronautic and aerospace structures due to their excellent mechanical properties. Their harsh service environment usually leads to aircraft surface pits, scratches, and other types of defects, which result in internal damages that reduce their strength, influencing their safety and reliability. With laser-controlled ablation, surface damage removal was implemented. However, the multiscale characteristics of plain-woven CFRP (macroscopic plain-woven textiles, mesoscopic fiber clusters, together with microscopic fiber and epoxy resin) lead to complex thermal–mechanical ablation action, prone to secondary surface damages and resin residue. Aiming at the requirement of high-performance removal of the damaged zone, a comprehensive investigation of the influence of laser ablation strategies, including the wavelength, defocus distance, scanning speed, hatch distance, scanning passes, etc., on generating morphologies was conducted. Results identified that the severe anisotropy of plain-woven CFRP gained a wide heat-affected zone (HAZ), which was restrained by adopting an ultraviolet (UV) laser ablation means. A high-quality laser ablation zone without visible resin residue and broken carbon fiber has been presented by one-pass laser ablation when a particular scarfing conditions combination was used. Meanwhile, a depth-controlled surface-forming approach was gained, accompanied by multiple laser scanning. Subsequently, a hybrid laser treatment strategy was provided for characteristic structure generation, and a novel stepwise structure was constructed for verification.

Development of a Procedure for Torsion Measurement Using a Fan-Shaped Distance Meter System.

Maximising the efficiency of wind turbines is crucial for sustainable development of renewable energy. In this context, monitoring and optimising rotor blade performance is becoming increasingly important, especially rotor blade deformation and torsion. We developed an approach for marker-free and contactless measurement of rotor blades during operation. Deformations of rotor blades can be recorded, with focus on torsion measurement. An innovative measuring system, named the fan-shaped distance meter system (FDMS), uses a combination of multiple laser scanners and photogrammetry. The focus of this work is to analyse the suitability of the FDMS for torsion measurement. We designed a torsion simulator to assess the achievable accuracy. Computer simulations and initial laboratory tests have demonstrated precise torsion measurements are possible using this method with an accuracy of 0.3°. Measurements can be carried out during operation of the wind turbine without the need to apply markers or sensors on rotor blades. By precisely recording the deformation and, in particular, torsion of rotor blades, targeted optimisation measures can be obtained in order to maximise performance of wind turbines. This innovative approach to measure the torsion of rotor blades in operation might offer great potential to increase the efficiency and life cycle of wind turbines.

Tailoring the Microstructure of Laser-Additive-Manufactured Titanium Aluminide Alloys via In Situ Alloying and Parameter Variation

Titanium aluminide (TiAl) alloys have emerged as promising materials for high-temperature applications due to their unique combination of high-temperature strength, low density, and excellent oxidation resistance. However, the fabrication of TiAl alloys using conventional methods is challenging due to their high melting points and limited ductility. Selective laser melting (SLM), an additive manufacturing technique, offers a viable solution for producing TiAl alloys with intricate geometries and the potential for tailoring their microstructure. This study investigates the effect of in situ copper alloying and multiple laser scans on the microstructure and mechanical properties of TiAl-based alloys fabricated using SLM. The results demonstrate that copper alloying enhances the formation of the α2-Ti3Al phase, refines the microstructure, and improves the mechanical properties of TiAl alloys. Multiple laser scans allow for the creation of distinct microstructural regions within a single component, enabling the tailoring of properties that are suitable for specific operating conditions. The findings provide valuable insights into the fabrication and optimization of TiAl intermetallic alloys with diverse applications.

Slope stability evolution of a deep‐seated landslide considering a constantly deforming topography

AbstractSlow‐moving deep‐seated landslides are characterised by continuous deformation, constantly changing topography and sliding‐mass geometry. Deformation rates are predominantly controlled by temporal dynamics of pore pressure. Progressing movements typically cause an over‐steepening of a landslide's foot, making these areas more susceptible to secondary slope failures and piggyback slides that, once they occur, change the geometric boundary conditions of a slope. This study presents an integrated topographic monitoring and geomechanical modelling approach, which is suitable for both model‐based replication of the landslide's hydro‐meteorological drivers and assessment of the long‐term effect of topographic changes on the stability behaviour of a large deep‐seated landslide. Parametrised at the Vögelsberg landslide (Tyrol, Austria) the integrated approach quantified considerable mass relocations between 2007 and 2020 at the landslide's foot and assessed respective effects on slope stability. Additionally, scenarios of past and future topographies were reconstructed and projected. Mass relocations of the order of 25 000 m3 were assessed between multiple airborne laser scanning acquisitions covering a period of 13 years. Based on annual uncrewed aerial vehicle laser scanning campaigns, area‐wide 3D displacements were analysed, exceeding a magnitude of 200 cm a−1 at small parts (2.500 m2) on the steeper foot of the active landslide. The main landslide body (0.28 km2) moves considerably slower with movements of 2–10 cm a−1. Besides spatio‐temporally varying hydrological drivers, topographic changes can have a severe impact on slope stability and therefore modify the spatiotemporal activity of the landslide. It is shown that, besides the hydrometeorological drivers, the varying elevation of the landslide's toe is a key parameter determining the long‐term trend of slope stability. With the presented approach the formation and evolution of the Vögelsberg landslide can be understood and explained.

Platelet Membrane Cloaked Nanotubes to Accelerate Thrombolysis by Thrombus Clot-Targeting and Penetration.

Thrombotic diseases have a high rate of mortality and disability, and pose a serious threat to global public health. Currently, most thrombolytic drugs especially protein drugs have a short blood-circulation time, resulting in low thrombolytic efficiency. Therefore, a platelet membrane (Pm) cloaked nanotube (NT-RGD/Pm) biomimetic delivery system with enhanced thrombolytic efficiency is designed. Nanotubes (NT) with an excellent clot-penetration properties are used to load a protein thrombolytic drug urokinase (Uk). Platelet-targeting arginine glycine-aspartic peptide (RGD) is grafted onto the surface of the nanotubes (NT-RGD) prior to cloaking. Multiple particle tracking (MPT) technique and confocal laser scanning microscope (CLSM) analysis are applied and the results show that the nanotubes possess a strong penetration and diffusion capacity in thrombus clots. After the Pm cloaking on NT-RGD/Uk, it shows a thrombus microenvironmental responsive release property and the half-life of Uk is six times longer than that of free Uk. Most importantly, NT-RGD-Uk/Pm exhibits a 60% thrombolytic efficiency in the FeCl3 -induced thrombosis mouse model, and it is able to significantly reduce the bleeding side effects of Uk. This Pm-cloaked nanotube system is an effective and promising platform for the controlled and targeted delivery of drugs for the thrombus treatment.

Laser direct Cu patterning utilizing a commercially available low-cost 3D printer

This study evaluated an inexpensive 3D printer (below 1000 USD) as a cost effective laser direct writing machine. This printer was applied to patterning copper (Cu) electrodes along with characterizing laser modules, such as the power stability of the laser, scan speed, pattern width against laser power, and position precision of the pattern. The laser power, controlled by a pulse width modulation signal, fluctuated by approximately 7 % and decreased by 2.1 % during the measurement period. After multiple laser scanning, the positional stability according to the thickness of the patterned Cu line showed a difference of up to 3.5 μm at the center of the line pattern. Depending on the laser power, line defects appearing at the center of the Cu patterns were observed at the focal length of the laser and disappeared at longer or shorter focal lengths. As the laser power was increased from 6.3 % to 100 %, the width of the patterned Cu lines increased from 22 to 246 μm. This appears to be due to the light scattering of the Cu crystals that form early when the laser is incident. A 143 nm thick 1 cm2 Cu pattern exhibited a resistance of 2.6 × 10−5 Ω·cm. Because this method uses a 3D printer that can control the z-height during laser processing, a Cu pattern-actuated LED on a three-dimensional glass surface was demonstrated using a set of experimental conditions based on the results.

Effect of powder bed preheating on the crack formation and microstructure in ceramic matrix composites fabricated by laser powder-bed fusion process

Ceramic matrix composites like cermets are difficult candidates to be fabricated by additive manufacturing (AM). Green cermets like the TiC-430 L AISI ferritic stainless steel (430 L-FSS) have been fabricated using the AM process like laser powder-bed fusion (LPBF) process or also known as selective laser melting (SLM). Multiple laser scanning was employed as a tool to preheat and melt the powder bed with different laser scanning parameters for each (two laser scans namely pre-heating scan and melting scan) scan to fabricate crack-free cermets. As a part of the preheating scanning (PHS) and melting scans (MS), different laser energy parameters are used to study the microstructure evolution and to study their densification process and mechanical properties. Lowering the preheating and melting scan speed results in prolonged laser exposure and higher temperature in the powder bed and melt pool, which led to the refinement of the microstructure due to higher cooling rate and generation of the cracks in the as-built parts caused by thermal gradient in the melt pool. Scanning electron microscopy and X-ray diffraction were performed to study the microstructure and phase analysis of the fabricated sample. Mechanical properties like density, hardness, fracture toughness, and compression tests were performed and discussed in detail. The results suggest that the laser PHS can effectively eliminate the presence of cracks. On the other hand, increasing the energy density of both PHS and MS results in a coarser microstructure with porosity, which also hampers the fracture toughness of these SLM fabricated cermets.

Characterization and calibration of multiple 2D laser scanners.

This paper presents the comparative evaluation of multiple compact and lightweight 2D laser scanners for their possible backpack based scanning and mapping applications. These scanners include Hokuyo URG-04LX, Slamtec RPLidar A1-M8 and Hokuyo UTM-30LX-EW scanners. Since the technical datasheets provide general information and limited working details, this research presents a thorough study on the performance of each scanner related explicitly to indoor mapping operations. A series of scanning experiments have been performed for the characterization of each scanner using statistical analysis. During the testing, all the scanning data has been recorded using Robot Operating System (ROS) and then computed in offline processing. In initial tests, each scanner’s drift effect on range measurements has been tested and presented in the relevant section of the paper. In continuation, the effect of various scanning distances on measurement accuracy has been evaluated and discussed. Later the impact of various materials typically found in indoor vicinities and their respective properties of color and smoothness have been tested and provided in the paper. Finally, a Kalman Filtering based mathematical formulation has been utilized to calibrate each scanner and to reduce the measuring uncertainties as observed in various tests for each scanner.

The effect of line-by-line laser scanning on the properties of laser-induced graphene

Technology of polyimide (PI) film carbonization by direct laser treatment attracts much attention due to the versatility and ease of obtaining the carbon material, laser-induced graphene (LIG), used in the creation of various sensors and functional devices. In this work LIG film structures are obtained by line-by-line scanning of a cw CO2 laser beam over the surface of the PI film. The synthesized carbon film material is studied by optical and scanning electron microscopy, X-ray photoelectron spectroscopy and Raman spectroscopy. It is shown that the Raman spectra of a single LIG line and a set of overlapping LIG lines significantly differ from each other. It is found that multiple laser scanning of the PI film leads to a marked decrease in the number of defects in the LIG structure as well as to a significant decrease in the specific surface resistance of the synthesized film material. The results obtained can be used in the synthesis of LIG film structures with improved characteristics. Keywords: laser-induced graphene, polyimide film, line-by-line laser scanning.

Влияние построчного лазерного сканирования на свойства лазерно-индуцированного графена

Technology of polyimide (PI) film carbonization by direct laser treatment attracts much attention due to the versatility and ease of obtaining the carbon material, laser-induced graphene (LIG), used in the creation of various sensors and functional devices. In this work LIG film structures are obtained by line-by-line scanning of a continuous CO2 laser beam over the surface of the PI film. The synthesized carbon film material is studied by optical and scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. It is shown that the Raman spectra of a single LIG line and a set of overlapping LIG lines significantly differ from each other. It is found that multiple laser scanning of the PI film leads to a marked decrease in the number of defects in the LIG structure as well as to a significant decrease in the specific surface resistance of the synthesized film material. The results obtained can be used in the synthesis of LIG film structures with improved characteristics.

Correlation of cells with proteins in extracellular polymeric substance matrix of bioaggregates

The bioaggregates for wastewater treatment are made of cells and the extracellular polymeric substances (EPS) secreted by the cells. This study performed multiple fluorescence staining technique and confocal laser scanning microscope (CLSM) observations to probe the spatial distributions of cells, proteins, and α-polysaccharides in the activated sludge flocs and the aerobic granule. The pair correlation analysis revealed that the cells have high affinity to proteins instead of to polysaccharides. Based on the patterns of the pair correlation functions, the sludge floc was shown to be a matrix reinforced by α-polysaccharides with embedded microaggregates of cells and proteins of size of 2–3 cell diameters.

Quantifying Crown Morphology of Mixed Pine-Oak Forests Using Terrestrial Laser Scanning

Mixed forests make up the majority of natural forests, and they are conducive to improving the resilience and resistance of forest ecosystems. Moreover, it is in the crown of the trees where the effect of inter- and intra-specific interaction between them is evident. However, our knowledge of changes in crown morphology caused by density, competition, and mixture of specific species is still limited. Here, we provide insight on stand structural complexity based on the study of four response crown variables (Maximum Crown Width Height, MCWH; Crown Base Height, CBH; Crown Volume, CV; and Crown Projection Area, CPA) derived from multiple terrestrial laser scans. Data were obtained from six permanent plots in Northern Spain comprising of two widespread species across Europe; Scots pine (Pinus sylvestris L.) and sessile oak (Quercus petraea (Matt.) Liebl.). A total of 193 pines and 256 oaks were extracted from the point cloud. Correlation test were conducted (ρ ≥ 0.9) and finally eleven independent variables for each target tree were calculated and categorized into size, density, competition and mixture, which was included as a continuous variable. Linear and non-linear multiple regressions were used to fit models to the four crown variables and the best models were selected according to the lowest AIC Index and biological sense. Our results provide evidence for species plasticity to diverse neighborhoods and show complementarity between pines and oaks in mixtures, where pines have higher MCWH and CBH than oaks but lower CV and CPA, contrary to oaks. The species complementarity in crown variables confirm that mixtures can be used to increase above ground structural diversity.

Nanosecond laser-assisted micro-scribing of a copper film on a dielectric material with laser-induced breakdown spectroscopy based monitoring

Pulsed laser-based material removal is a preferred micro-scribing technique for Copper (Cu) cladded onto an insulating substrate, such as a flame-retardant glass-reinforced epoxy resin (FR4), because of the less thermal diffusion as well as the process flexibility. This paper reports the pulsed laser-assisted micro-scribing of Cu (35 µm) from a dielectric material. The process was monitored by laser-induced breakdown spectroscopy technique (LIBS). For the complete removal of Cu from the substrate material, multiple laser scans were required. The Cu I line intensity in the LIBS spectra was decreasing with an increase in the microchannel depth. During the final laser scan, the FR4 substrate was getting ablated, and in the LIBS spectra, the characteristic emission lines from the substrate elements such as Calcium (Ca), Aluminum (Al), Sodium (Na) and Silicon (Si) were observed. The depth for a single laser pulse was estimated from a theoretical model, including the melt ejection due to the recoil pressure. Approximate microchannel depth was predicted based on the theoretical simulation.

Target-based automated matching of multiple terrestrial laser scans for complex forest scenes

Terrestrial laser scanners are widely used to derive unbiased and non-destructive estimates of the vertical distribution of the plant area index and plant area volume density at plot-level scales, as well as the above-ground biomass, height, and diameter at breast height of individual trees. Multiple scans are often employed to capture and register data so that all of the stems can be detected and their complete forms can be analyzed. Researchers have traditionally preferred target-less strategies to register scans because of their low cost and convenience. However, in complex forest scenes, even state-of-the-art approaches cannot guarantee the success of any pairwise registration. In this study, we present an automated target-based processing approach for the registration of unordered scans in complex forest scenes. In contrast to previous studies, the proposed registration method automatically detects the artificial targets and builds a geometric network to judge their connectivity. A pose graph is then exploited to combine these data with the corresponding pairwise transformation, and then the scans are integrated into a unified coordinate system. This method is more robust and efficient than target-less approaches because it is independent of the characteristics of individual trees and does not require ground information. In an experimental scenario, we use an extremely complex wild bamboo forest scene to evaluate the performance of the proposed approach in terms of robustness, accuracy, and efficiency.

Selective Direct Laser Writing of Pyrolytic Carbon Microelectrodes in Absorber-Modified SU-8.

Pyrolytic carbon microelectrodes (PCMEs) are a promising alternative to their conventional metallic counterparts for various applications. Thus, methods for the simple and inexpensive patterning of PCMEs are highly sought after. Here, we demonstrate the fabrication of PCMEs through the selective pyrolysis of SU-8 photoresist by irradiation with a low-power, 806 nm, continuous wave, semiconductor-diode laser. The SU-8 was modified by adding Pro-Jet 800NP (FujiFilm) in order to ensure absorbance in the 800 nm range. The SU-8 precursor with absorber was successfully converted into pyrolytic carbon upon laser irradiation, which was not possible without an absorber. We demonstrated that the local laser pyrolysis (LLP) process in an inert nitrogen atmosphere with higher laser power and lower scan speed resulted in higher electrical conductance. The maximum conductivity achieved for a laser-pyrolyzed line was 14.2 ± 3.3 S/cm, with a line width and thickness of 28.3 ± 2.9 µm and 6.0 ± 1.0 µm, respectively, while the narrowest conductive line was just 13.5 ± 0.4 µm wide and 4.9 ± 0.5 µm thick. The LLP process seemed to be self-limiting, as multiple repetitive laser scans did not alter the properties of the carbonized lines. The direct laser writing of adjacent lines with an insulating gap down to ≤5 µm was achieved. Finally, multiple lines were seamlessly joined and intersected, enabling the writing of more complex designs with branching electrodes and the porosity of the carbon lines could be controlled by the scan speed.

Voxel-Based Automatic Tree Detection and Parameter Retrieval from Terrestrial Laser Scans for Plot-Wise Forest Inventory

This paper presents a fully automatic method addressing tree mapping and parameter extraction (tree position, stem diameter at breast height, stem curve, and tree height) from terrestrial laser scans in forest inventories. The algorithm is designed to detect trees of various sizes and architectures, produce smooth yet accurate stem curves, and achieve tree height estimates in multi-layered stands, all without employing constraints on the shape of the crown. The algorithm also aims to balance estimation accuracy and computational complexity. The method’s tree detection combines voxel operations and stem surface filtering based on scanning point density. Stem diameters are obtained by creating individual taper models, while tree heights are estimated from the segmentation of tree crowns in the voxel-space. Twenty-four sample plots representing diverse forest structures in the south boreal region of Finland have been assessed from single- and multiple terrestrial laser scans. The mean percentages of completeness in stem detection over all stand complexity categories are 50.9% and 68.5% from single and multiple scans, respectively, while the mean root mean square error (RMSE) of the stem curve estimates ranges from ±1.7 to ±2.3 cm, all of which demonstrates the robustness of the algorithm. Efforts were made to accurately locate tree tops by segmenting individual crowns. Nevertheless, with a mean bias of −2.9 m from single scans and −1.3 m from multiple scans, the algorithm proved conservative in tree height estimates.