Showing papers in "Journal of Laser Applications in 2014"
TL;DR: In this article, the effects of preheating during selective laser melting (SLM) of aluminum components were investigated and an appropriate pre-heating temperature at which distortion practically no longer occurs was determined.
Abstract: The additive manufacturing process selective laser melting (SLM) can be used to directly produce functional components made out of metal. During the construction process, however, thermally induced residual stress occurs due to the layered build-up and the local input of energy by means of a focused laser beam, which can lead to distortion of the component or sections of the component itself. Normally, distortion is prevented due to supporting structures between the component and the substrate plate. It is not always possible, however, to provide all the areas of a component with supporting structures or to remove them later, depending on how complex the geometry or how accessible the structures are. When the substrate plate is heated during the construction process, the distortion can be reduced or eliminated entirely. Nonetheless, a systematic investigation of the extent to which preheating influences distortion of aluminum components has not yet been conducted. This works aims at systematically investigating the effects of preheating during SLM of aluminum components and determining an appropriate preheating temperature at which distortion practically no longer occurs. A significant reduction in distortion compared to the distortion without preheating can be seen beginning at a preheating temperature of 150 °C. At a preheating temperature of 250 °C, distortion can no longer be detected within the scope of the measuring accuracy independent of the twin cantilever test geometry investigated. In addition to reducing distortion, the preheating avoids the stress-related cracks in the component, which can lead to tearing of the parts of the test geometry. With 90 HV 0.1 at a preheating temperature of 250 °C, the hardness is greater than the required minimum hardness according to DIN EN 1706 of die-cast parts from the material AlSi10Mg. From these results, it can be concluded that a preheating temperature of 250 °C is suitable for reliably manufacturing components made out of the material AlSi10Mg using SLM free of defects and for preventing distortion completely.
284 citations
TL;DR: In this article, a complete modeling of heat and fluid flow applied to laser welding regimes is proposed, which can be easily usable in industrial R&D environments using only a graphical user interface of a finite element commercial code.
Abstract: A complete modeling of heat and fluid flow applied to laser welding regimes is proposed. This model has been developed using only a graphical user interface of a finite element commercial code and can be easily usable in industrial R&D environments. The model takes into account the three phases of the matter: the vaporized metal, the liquid phase, and the solid base. The liquid/vapor interface is tracked using the Level-Set method. To model the energy deposition, a new approach is proposed which consists of treating laser under its wave form by solving Maxwell's equations. All these physics are coupled and solved simultaneously in Comsol Multyphysics®. The simulations show keyhole oscillations and the formation of porosity. A comparison of melt pool shapes evolution calculated from the simulations and experimental macrographs shows good correlation. Finally, the results of a three-dimensional simulation of a laser welding process are presented. The well-known phenomenon of humping is clearly shown by the model.
104 citations
TL;DR: In this article, reinforcement, undercut, and root drop-through during laser hybrid arc welding of steel were studied in dependence of gap width, welding speed, and wire feeding rate.
Abstract: Reinforcement, undercut, and root drop-through during laser hybrid arc welding of steel were studied in dependence of gap width, welding speed, and wire feeding rate. Generalized trends were obtained through design of experiments. Most of the trends could be explained by a mass balance while some parameter impacts relied on more complex mechanisms. In particular, different levels of complexity of parameter dependencies were distinguished, ranging from monotonous behaviour to maxima and to changing signs of the trends. The findings are of high practical relevance to optimize the process with respect to the weld quality. Moreover, the potential and limits of the design of experiments method, of a mass balance, and of the matrix flow chart method are discussed.
29 citations
TL;DR: In this article, different fundamental investigation methods to determine the optical and thermal material characteristics like the thermal diffusivity, thermal conductivity, or the influence of different heating rates on the melting behavior are presented.
Abstract: By selective laser sintering (SLS), polymer powders are molten layer by layer to build conventional prototypes or parts in small series with geometrical freedom that cannot be achieved by other manufacturing technologies. The SLS process is mainly defined by the beam–matter interaction between powder material, laser radiation and different material characteristics by itself. However the determination of these different material characteristics is problematic because powder material imposes certain requirements that cannot sufficiently be provided by conventional measurement methods. Hence new fundamental investigation methods to determine the optical and thermal material characteristics like the thermal diffusivity, thermal conductivity, or the influence of different heating rates on the melting behavior are presented in this paper. The different analysis methods altogether improve the process of understanding to allow recommendations for the future process controlling.
29 citations
TL;DR: In this paper, a method to fabricate periodic silicon antireflection surface structures using direct four-beam laser interference lithography (LIL) was presented, which can convert conical spikes structure into an array of holes.
Abstract: Silicon surface structures with excellent antireflection property arouse wide interest. Chemical and physical methods such as femtosecond, nanosecond, and picosecond laser processing, wet-chemical etching, electrochemical etching, and reactive ion etching have been developed to fabricate them. However, the methods can only produce a quasi-ordered array of sharp conical microspikes on silicon surface. In this paper, we present a method to fabricate periodic silicon antireflection surface structures using direct four-beam laser interference lithography (LIL). With 1 atm ambient atmosphere of SF6 and the laser fluence of the four beams irradiated on the silicon surface at 0.64 J cm−2, the periodical conical spikes were generated. Changing the polarization directions of the opposite incident beam pairs in a four-beam LIL system could convert conical spikes structure into an array of holes. Antireflection in a wide spectral range was measured by a spectrophotometer from ultraviolet to near-infrared. The average reflectance of this periodic black silicon surface is less than 3.5%.
26 citations
TL;DR: In this article, the absorptivity of a laser beam interacting at grazing incidence with the processing front during laser welding, cutting, or drilling depends on the metal to be processed and on the laser wavelength.
Abstract: The absorptivity of a laser beam interacting at grazing incidence with the processing front during laser welding, cutting, or drilling depends on the metal to be processed and on the laser wavelength. The absorptivity on a smooth processing front is homogeneously governed by the angle-dependent operating range of the corresponding Fresnel-curve. In contrast, a wavy processing front strongly modulates the absorptivity across the surface. The calculated absorptivity modulation is presented for five different metals and four laser wavelengths. A discussion based on the respective optical constants and Fresnel-curves leads to a categorization of the absorption behavior, mainly dividing into low and high electrical conductivity metals as well as into short and 10.6 μm long laser wavelength. Six categories are distinguished. In particular, highly conductive metals remain highly reflective for short laser wavelength, even for a wavy processing front. Exceptions of higher overall absorptance are Cu for 532 nm and Al for 808 or 532 nm.
22 citations
TL;DR: In this paper, an elongated keyhole can be created by surface tension effects in the melt which can generate a self-sustaining geometry at the rear of the melt pool.
Abstract: During laser keyhole welding of thin plates, the melt pool is relatively wide compared to the plate thickness. Under certain conditions, an elongated keyhole can be created and a permanent hole is sometimes left in the weld seam. The generation of such holes is determined by surface tension effects in the melt which can generate a self-sustaining geometry at the rear of the melt pool. The geometry of the shape is known as a catenoid and has clear geometrical limits.
20 citations
TL;DR: In this article, the effect of thermal properties on the power density value necessary to achieve melting and vaporization in three different materials, including aluminum, mild steel, and stainless steel, was investigated.
Abstract: Aluminum, mild steel, and stainless steel have very dissimilar thermal properties. This study focuses on the effect of power density on the laser welding conduction mode limit in these three materials. The objective is to evaluate how these different materials will behave in conduction mode and in keyhole mode and also to understand how the thermal properties of the materials will influence the transition between the different welding modes. A comparison between the penetration depth and the melted area for the different materials under the same conditions was also made. The experimental results show that thermal properties conductivity, melting temperature, vaporization temperature, and thermal diffusivity have an important role in the transition between the welding modes. An analytical model was developed in order to study the effect of thermal properties on the power density value necessary to achieve melting and vaporization in these materials. Also all three materials showed a transition mode between the conduction mode and the keyhole mode. Aluminum had higher penetration efficiency in conduction mode and in the transition mode. However, in the keyhole mode, all three materials had very similar penetration efficiency.
19 citations
TL;DR: In this article, a comprehensive overview of the reported research with respect to laser assisted CVD for the growth of carbon nanotubes is given, with a focus on structural quality and properties, such as length, position and alignment.
Abstract: Laser-assisted chemical vapor deposition (LACVD) is an attractive maskless process for growing locally carbon nanotubes at selected places on substrates that may contain temperature-sensitive components. This review gives a comprehensive overview of the reported research with respect to laser assisted CVD for the growth of carbon nanotubes. The advantages and disadvantages of local growth using laser sources are discussed, with a focus on structural quality and properties, such as length, position and alignment, and process control. The paper is divided into two parts. The first part deals with the influence that the main parameters for nanotube growth—gas, catalyst and thermal energy—have on the growth of carbon nanotubes by laser-assisted synthesis. The second part deals with the attempts and successes to control different aspects of local nanotube growth using a laser-assisted growth method.
19 citations
TL;DR: In this paper, a modified trim cut method with low level of invasion into the process is developed for visualization of laser cutting process, which consists in high speed filming via transparent plate which slides with respect to the metal to allow visual access and simultaneously serves as the second missing wall.
Abstract: Modified trim cut method with low level of invasion into the process is developed for visualization of laser cutting process. The method consists in high speed filming via transparent plate which slides with respect to the metal to allow visual access and simultaneously serves as the second missing wall of the kerf. The method is suitable for visualization in conditions equivalent to industrial cutting process in a wide range of plate thicknesses. High speed recordings are done for cutting of mild steel with oxygen and stainless steel with nitrogen. The effect of radiation wave length on the surface quality is studied by comparison of CO2 and fiber laser processing. The obtained results suggest that in case of oxygen assisted cutting, the combustion effects dominate on the surface quality and the effect of the radiation wavelength is moderate. In contrast, inert-gas-assisted cutting visualization reveals very high sensitivity to hydrodynamics of the melt flow which is strongly dependent on the radiation wavelength.
18 citations
TL;DR: In this paper, a digital micromirror device is used as an intensity spatial light modulator, in conjunction with a femtosecond laser, for programmable image-projection-based laser ablation of polycrystalline diamond.
Abstract: A digital micromirror device is used as an intensity spatial light modulator, in conjunction with a femtosecond laser, for programmable image-projection-based laser ablation of polycrystalline diamond. Results show the machining of complex structures on the diamond surface, where individual structures have submicron features, covering a total area of 10 × 10 μm and fabricated using ten laser pulses. This dynamic image-based machining technique may offer speed advantages over serial-writing procedures, whilst still producing wavelength-scale feature sizes.
TL;DR: In this paper, the characteristics of laser-induced periodic surface structures are investigated after laser irradiation with a pulse duration (10 ps) under a certain laser fluence (0.27 J/cm2) and pulse number (N = 50-2000).
Abstract: The characteristics of laser-induced periodic surface structures are investigated after laser irradiation with a pulse duration (10 ps) under a certain laser fluence (0.27 J/cm2) and pulse number (N = 50–2000). In the experiments, at the lowest number of pulses, ultrafine ripples are observed with sub-200-nm spatial periods and an orientation parallel to laser polarization direction. With the increasing pulse number, a chain of events that has been observed consists of ultrafine ripples followed by a transformation towards regular ripples with an orientation perpendicular to laser polarization direction and holes finally breaking regular ripples. Although the generation of ultrafine and regular ripples upon laser irradiation is a universal phenomenon, the origin behind the transition is discussed here to help understand the exact physical mechanism and their occurrence with their dependence on the irradiation parameters.
TL;DR: In this paper, the geometrical conditions of the melt flow can be tailored to suppress undercut when using the arc leading setup, which can be seen that the keyhole and its position affects the melting flow, making the distance between the laser and the arc an important parameter.
Abstract: In welding, high welding speeds are usually limited by an increase in undercut. This study shows that the geometrical conditions of the melt flow can be tailored to suppress undercut when using the arc leading setup. By applying high speed imaging, it can be seen that the keyhole and its position affects the melt flow, making the distance between the laser and the arc an important parameter. Undercut formation usually occurs due to a narrowing or necking of the melt flow behind the gouge that can be prevented if the melt flow is changed by optimizing the laser/arc positioning.
TL;DR: In this article, a hybrid process for joining high material thicknesses was proposed, which combines a laser beam and two gas metal arc (GMA) welding torches in one setup.
Abstract: Hybrid processes have been established for the joining of thick plates. The presented approach enables single side welding of thick metal plates by combining a laser beam and two gas metal arc (GMA) welding torches in one setup. By using this hybrid process for joining high material thicknesses, manufacturing time can be significantly reduced in comparison to conventional multilayer arc welding processes. Additionally, new joint designs can be used to reduce filler metal consumption. In order to benefit from these economic advantages, and to make use of brilliant high power lasers in pipeline manufacturing, this hybrid process needs to run robustly for common gap and tolerance ranges. The process time, compared to conventional methods, will be significantly decreased, due to the use of disk lasers with a maximum output power of 16 kW combined with two high power GMA subprocesses. For process development, American Petroleum Institute (API) 5L X70 pipeline steel plates with a thickness of 23 mm have already been joined in a flat position using a single weld pass. Based on these parameter studies, the process limitations have been determined with regard to energy input, gap bridgeability, vertical edge offset, and a lateral offset of the energy sources from the weld joint. The robustness of the hybrid process developed has been demonstrated in experiments representative of the pipeline application.
TL;DR: In this paper, the dependence of photoluminescence (PL) spectra on annealing temperature and laser irradiation energy has been investigated, and the results from Hall measurements and the variation of visible emission indicated that both NN and LIR had the same influence on controlling the concentration and some native defects in ZnO thin films.
Abstract: Zinc oxide (ZnO) thin films were deposited on a sapphire (001) by pulsed laser deposition technique at room temperature. The profound changes of ZnO thin films had been observed. The large surface morphology difference of ZnO thin films between annealing and laser irradiation was found. Meanwhile, the dependence of photoluminescence (PL) spectra on annealing temperature and laser irradiation energy had been investigated. As the annealing temperature and laser irradiation energy increased, the PL intensity of visible luminescence decreased. In contrast, the intensity of ultraviolet (UV) emission increased largely with the increasing laser energy. However, annealing treatment had no effect on the UV emission behavior. The results from Hall measurements and the variation of visible emission indicated annealing and laser irradiation had the same influence on controlling the concentration and some native defects in ZnO thin films. Besides, the thermal and photochemical effects of KrF excimer led to an enormous accumulation of zinc interstitial, and the carrier concentration increased up to six orders of magnitude. Furthermore, the origins of UV and visible emissions were discussed.
TL;DR: In this article, a two-dimensional thermal model of nanosecond pulsed laser ablation is developed to describe the physical processes, the plasma absorption, the crater profile, and the temperature distribution on a gold target and below the surface.
Abstract: A two-dimensional thermal model of nanosecond pulsed laser ablation is developed to describe the physical processes, the plasma absorption, the crater profile, and the temperature distribution on a gold target and below the surface. The surface temperature and the plasma plume are coupled to the target through the Knudsen layer at the target–vapor interface. The simulation results of crater shape have been compared with the experimental outcomes obtained by a pulsed Nd:YAG laser having 1064 nm wavelength, 235 ns duration, 70 μm spot size on the target, and pulse energy of 2.5 mJ leading to the intensity less than 109 W/cm2. According to the model results the material removal process continues for a long time after the end of pulse irradiation, about 1200 ns after the beginning of the laser pulse irradiance. This model is valid when the phase explosion does not occur; it means that the target surface temperature is less than the critical value.
TL;DR: In this article, the laser weldability for tailor-welded blanks (TWBs) made of dissimilar hot-stamping steels was examined and the mechanical and metallurgical characteristics of the welds were then analyzed.
Abstract: In this research, the laser weldability for tailor-welded blanks (TWBs) made of dissimilar hot-stamping steels was examined. Usibor and Ductibor from ArcelorMittal were combined, since they are steels that possess a high-strength and high-energy absorption, respectively. Additionally, combination of Usibor and SPRC440 was investigated for comparison. After laser butt welding, the specimens were heat-treated at high temperatures, and the subsequent quenching conditions were similar to those in the hot-stamping process. The mechanical and metallurgical characteristics of the welds were then analyzed. The TWBs with Usibor and Ductibor exhibited a high degree of elongation after hot-stamping but those with Usibor and SPRC440 showed a relatively low elongation. The AlSi coating on the base metal was included in the fusion zone, and it led to ferrite formation. However, in the static and high-speed tensile tests, the AlSi coating did not affect the tensile strength of the TWBs, and all tensile specimens were fractured at the base metal of Ductibor.
TL;DR: In this article, hot cracks were found in a preferred geometrical window, namely, in the middle of the narrow deep region of the weld which was generated by the laser beam.
Abstract: Hot cracks were frequently found in double sided laser-arc hybrid welding thick section (20 mm) low carbon steel. Other research has usually investigated the metallurgical resolidification mechanisms of the welded metal alloy, but here possible relationships between the hot cracks and geometrical aspects of their surrounding weld and heat-affected zone cross sections were studied. The motivation behind this research was to identify guidelines for laser-arc hybrid welding to avoid hot cracks. Weld cross sections were used to analyze hot cracking because they are rather easy to prepare and straightforward to alter through the process parameters. In this study, hot cracks were found in a preferred geometrical window, namely, in the middle of the narrow deep region of the weld which was generated by the laser beam. From the cross section analysis, a first indicator was that a more inclined, converging shape of the lower part of the weld cross section can avoid hot cracks, associated with different energy input and resolidification front geometry. Significant reduction of the welding speed has avoided hot cracks, being a second indicator.
TL;DR: In this article, a new method of synthesis Ag/Au core/shell nanostructure with ultraviolet (UV) excimer laser was studied, and it was found Ag/AU core and shell nanostructures with spherical shell could be prepared by UV excimer Laser which was confirmed by high resolution transmission electron microscopy.
Abstract: A new method of synthesis Ag/Au core/shell nanostructure with ultraviolet (UV) excimer laser was studied. It was found Ag/Au core/shell nanostructures with spherical shell could be prepared by UV excimer laser which is obviously confirmed by high resolution transmission electron microscopy. The surface plasma resonance of this nanostructure can be tuned by controlling thickness of the Au shell. Simulation based on Mie theory was in agreement with the result of the experiments. Moreover, it is indicated the Ag/Au core/shell nanostructure has excellent activity in surface-enhanced Raman scattering. This Ag/Au core/shell nanostructure may be applied to high sensitive trace detection in the future.
TL;DR: In this article, a multibeam diffraction pattern using an adaptive optics is studied for laser cutting of thin metal sheets, together with liquid crystal on silicon spatial light modulator (SLM).
Abstract: Laser cutting with multibeam diffraction pattern using an adaptive optics is studied. Infrared (IR) continuous single-mode fiber laser with maximum power of 200 W is applied to laser cutting of thin metal sheets, together with liquid crystal on silicon spatial light modulator (SLM). SLM can be used as the adaptive diffractive optical element, which can modify intensity profile of the laser beam almost arbitrary. In studies single Gaussian laser beam was divided into multiple spots. It was found out that with this way it is possible to enhance the cutting quality and also decrease pressure of the needed assist gas. Multibeam configuration enabled to laser cut burr free with 50% less protection gas pressure compared to single beam laser cutting with conventional optics.
TL;DR: In this paper, a high average power passively Q-switched, laser diode side-pumped green laser at 532nm was reported by using Nd:YAG/Cr4+: YAG/YAG composite crystal for the first time.
Abstract: In this paper, a high average power passively Q-switched, laser diode side-pumped green laser at 532 nm was reported by using Nd:YAG/Cr4+:YAG/YAG composite crystal for the first time. The performances of the average power, pulse width, and pulse repetition rate on pump power were measured. Under the pump power of 187.5 W, the Q-switched green laser was obtained with the average power of 27.2 W, pulse width of 210 ns, and the repetition rate of 21.2 kHz. The single-pulse energy was 1.28 mJ and peak power was higher than 6.1 kW.
TL;DR: In this article, the authors summarized the state-of-the-art fabrication process of nPRMMCs by laser cladding via both ex-situ route and in-in situ route.
Abstract: The nanoparticulate reinforced metal matrix composites (nPRMMCs) can further improve the ductility and fracture toughness of conventional microscale PRMMCs. The uniform dispersion of nanosized hard particles in the matrix is vital due to their strong tendency to agglomerate. This paper summarizes the state-of-the-art fabrication process of nPRMMCs by laser cladding via both ex-situ route and in-situ route. Concerns have been focused on the uniform dispersion of nanoparticles and their interface bonding with the matrix. The current challenges and future developments are discussed. This summarization will be helpful for the further research on the fabrication and applications of nPRMMCs.
TL;DR: In this article, the effect of the scanned beam on the cladding process itself has been studied very thoroughly so far, and the results showed that both of these factors significantly influence the process stability and the outcome of the claddings process.
Abstract: Scanning optics is an effective way to manipulate a laser beam for laser cladding. The numerical adjustment of the scanner gives a great deal of flexibility to the cladding process. However, the effect of the scanned beam on the cladding process itself has not been studied very thoroughly so far. This study concentrates on explaining how the scanning frequency and power density of the laser beam affect the stability of the cladding process. The results showed that both of these factors significantly influence the process stability and the outcome of the cladding process. If the local specific energy input was over 2.46 J/mm2, the process was noticed to be unstable. This limit was cross when scanning frequency was under 40 Hz. Power density's limit value for stable process was found to be 191 kW/cm2 and higher power densities than this was found to produce unstable process. If the cladding process was found to be unstable, dilution increased significantly and process started to resemble more laser alloying.
TL;DR: In this article, the microstructure in the intermediate layer of a laser-welded Cu-Al lap joint was examined metallographically, and fracture surface analysis was also performed using scanning electron microscopy with energy dispersive spectroscopy.
Abstract: The microstructure in the intermediate layer of a laser-welded Cu–Al lap joint was examined metallographically. Tensile shear test was performed, and fracture surface analysis was also performed using scanning electron microscopy with energy dispersive spectroscopy. Results showed that there were several different zones with diverse characteristics of morphology and composition in the intermediate layer of the weld joint. Banded and cellular structures were observed in the hypereutectic zone; a lamellar structure was found in the eutectic zone which was the narrowest zone with the finest microstructure; a dendritic structure was obtained in the hypoeutectic zone with the coarsest microstructure and widest zone. The joint faulted in the dendritic hypoeutectic zone, under a combination of brittle and shear mode in the fracture surface. The maximum shear load of the Cu–Al joint decreased with increasing primary dendrite arm spacing and the growth of secondary dendrite in the hypoeutectic zone, which was induced by increasing laser power.
TL;DR: In this paper, the laser power was selected as the PID output parameter adjusted by the heat radiation signal to control the build-up shape of the weld pool during the LMD process.
Abstract: LMD (Laser Metal Deposition) is a technique used to repair damaged components and directly form three dimensional structures. From the aspect of productivity, improvement of the shape accuracy of the deposit is required to reduce machining process after LMD. Objective of this work is to control the build-up shape by adjusting the weld pool size. Configurations of deposits made with various LMD process conditions were measured in cross section. In addition, the signal intensity of heat radiation, plume emissions and laser reflections from the weld pool was monitored by photodiodes intergrated in laser processing head during LMD process. The results showed a strong correlation between weld pool size and signal intensity of heat radiation. Adaptive shape control system, which consists of in process monitoring system and PID (Proportional-Integral-Derivative) controller using that correlation, was developed to control build-up shape. Due to the liner relationship with weld pool size, laser power was selected as the PID output parameter adjusted by the heat radiation signal. Since the target value of the heat radiation signal can be changed flexibly during the LMD process in our PID control system, deposit shape is successfully controlled as required with sufficient profile accuracy of the build-up layers.
TL;DR: In this paper, the authors have generated Mn ferrite nanoparticles by Nd:YAG (1064 nm) laser irradiation in distilled water, and the results show that the chemical composition and magnetic properties of nanoparticles are nearly similar to bulk sample.
Abstract: In this work, the authors have generated Mn ferrite nanoparticles by Nd:YAG (1064 nm) laser irradiation in distilled water. Then, they have investigated shape and size of nanoparticles by transmission electron microscopy and atomic force microscope. Chemical composition of nanoparticle was characterized using dispersive x-ray energy, and the magnetic properties of them were studied by magnetic force microscopy. A spinel structure in nanoparticles similar to the bulk sample was shown by selected area electron diffraction. The results show that the chemical composition and magnetic properties of nanoparticles are nearly similar to bulk sample.
TL;DR: In this paper, the effect of variation of excimer laser fluences on the surface structuring of titanium (Ti) targets has been investigated, and the KrF excimer was employed for this purpose.
Abstract: The effect of variation of excimer laser fluences on the surface structuring of titanium (Ti) targets has been investigated. The KrF excimer laser (λ = 248 nm, t = 20 ns, repetition rate 20 Hz) has been employed for this purpose. The targets were irradiated for various laser fluences ranging from 0.86 J cm−2 to 1.27 J cm−2 under vacuum condition. Various diagnostic techniques like scanning electron microscope (SEM), atomic force microscope (AFM), and X-ray diffraction (XRD) have been utilized to investigate the surface topography and structural changes of laser ablated targets. SEM analysis reveals the formation of laser-induced periodic surface structures (LIPSS) at the central ablated region. The periodicity of LIPSS increases from 5 μm to 88 μm with the increase of fluence from 0.86 J cm−2 to 1.27 J cm−2. The formation of grains is observed at the peripheral ablated region for all laser fluences. Reduction in grain size from 7.7 μm to 3.8 μm is observed with increasing fluence from minimum to maximum value. AFM analysis exhibits the growth of several numbers of bumps and protrusions on irradiated targets. The height of bumps is reduced from 100 nm to 40 nm with increasing fluence. XRD analysis shows that no new phases were formed under vacuum condition for all fluence values. However, an alteration in the peak intensity, crystallinity, and d-spacing for various diffraction planes of Ti has been observed after irradiation.
TL;DR: In this article, the dependence of the pattern linewidth on variation in the processing parameters, like the laser patterning velocity or power of the femtosecond laser oscillator, is presented.
Abstract: In this work, the authors report on investigations of two-photon lithography of positive photoresist. The dependency of the pattern linewidth on variation in the processing parameters, like the laser patterning velocity or power of the femtosecond laser oscillator, is presented. The influence of the scan velocity between 0.38 and 1.90 mm/s on the resolution is discussed for a layer thickness of 3.5 μm. By using a commercial positive photoresist, an aspect ratio of 5 has been realized for grid structures and the qualities of the produced structures are discussed.
TL;DR: According to the results of the study, statistically significant differences were determined between the control group and the other groups in the removal of the smear layer from the root canals (p < 0.05).
Abstract: The aim of this study is to analyze the efficiency of different laser systems and irrigating solutions on the removal of superficial debris and smear layer created during instrumentation in root canals. Seventy two extracted human maxillary canine teeth were sectioned and the root canals were prepared. The specimens were divided randomly into equal six groups as follows: 5.25% NaOCl in group 1 (control group), 15% ethylenediaminetetraacetic acid (EDTA) for 1 min followed by 5.25% NaOCl in group 2, 25% citric acid for 1 min followed by 5.25% NaOCl in group 3 were applied into the root canals. In the other groups treated with only laser, diode laser (2 W, 10 Hz) in group 4, Er:YAG laser (1 W, 10 Hz) in group 5, and Nd:YAG laser (1 W, 10 Hz) in group 6 were applied to the root canals. Photomicrographs were taken from the coronal, middle, and apical thirds of specimens by using scanning electron microscope. Statistical analyses were performed with Kruskal–Wallis and Mann–Whitney U tests (p = 0.05). On account of superficial debris, statistically significant differences were presented between the groups. According to the results of the study, statistically significant differences were determined between the control group and the other groups in the removal of the smear layer from the root canals (p < 0.05). Superficial debris was effectively removed by Er:YAG and diode laser. Combinations of EDTA + NaOCl and citric acid + NaOCl removed most effectively the smear layer.
TL;DR: In this article, it is shown that it is possible to reduce undercut at the weld cap and smooth out the weld root profile by defocussing the welding laser and using it to remelt the welded surfaces.
Abstract: Laser welding, arc welding, and laser-arc hybrid welding can all result in undercut and varying penetration. In some cases, it is technically and commercially viable to reduce undercut at the weld cap and smooth out the weld root profile by defocussing the welding laser and using it to remelt the welded surfaces.