Small Spot Diameter Research Articles

Determination of anthracnose (Colletotrichum gloeosporioides) resistance group in shallot (Allium cepa var. aggregatum)

Shallot anthracnose, caused by Colletotrichum gloeosporioides, is a devastating disease in a tropical country with high humidity and rainfall. Chemical control of anthracnose is neither economical nor eco-friendly, and genetic resistance is considered an efficient management method. This study aimed to determine the resistance groups of several shallot varieties and predict resistance heritability characteristics. In this study, a total of 13 Indonesian shallot varieties were evaluated for anthracnose resistance and separated into two groups, resistance and susceptible, based on K-means clustering developed by using disease resistance/susceptibility characteristics such as incubation period, disease incidence, disease severity, and spot diameter. The results indicate that the Agrihorti, Maja Cipanas, Batu Ijo, and Rubaru varieties were identified as resistant groups based on lower disease severity and incidence, smaller spot diameter, and longer incubation period. Maja Cipanas and Rubaru were more consistent in all variables, which is recommended as a source of genetic resistance genotypes. On the other hand, the Biru Lancor, Bima Brebes, Srikayang, Violetta, Slupu Merah, Pancasona, Sakato, Katumi, and Kuning varieties were identified as susceptible groups based on high disease severity and incidence, large spot diameter, and short incubation period.
 Keywords: susceptibility characteristics, genetic resistance, k-means clustering, disease severity

Bessel beam generated LIPSS on NiTi wires

Ultrashort laser pulses are used to generate Laser-Induced Periodic Surface Structures (LIPSS). To apply LIPSS on small confined areas, the laser source must be focused to a small spot diameter. Contrary to commonly used high numerical aperture objectives, we present a Bessel beam-based approach to produce LIPSS covered lines with a width of 4 to 10 µm. Therefore, an 800 nm Ti:Sa-laser with a pulse duration of 110 fs and a repetition rate of 5000 Hz was used. The setup convinces with an extended depth of focus. Thus, high reproducibility of the process was proven, while no focus control and no specific requirements for the surface quality are needed. The applicability of this method is demonstrated by structuring the shell surface of nickel–titanium wires.

Crystal growth control of Ni-based alloys by modulation of the melt pool morphology in DED

In additive manufacturing especially in directed energy deposition, it is hard to control crystal growth pattern due to the high temperature gradient in AM. Essentially, the crystal grows epitaxially from the substrate and columnar crystals with strong texture are exhibited in AM components. Here, small spot diameter was used for DED-L of Ni-based alloys and various crystal growth patterns were obtained by changing power density. Samples processed under low power density were shown to exhibit wide and shallow spindle-like melt pool, along with apparently hierarchical planar-columnar-equiaxed microstructure. While samples prepared under relatively high power density were shown to exhibit narrower and deeper melt pool with two sharp turning points, exhibiting inclined columnar grains and several discontinuous central axial columnar crystals. When highest power density and small spot diameter were applied, crystal growth with weak texture was achieved. Under this deep and narrow melt pool, the crystal growth can be separated into four regions: nearly-equiaxed grains with random grain orientations; horizontally symmetrically grown crystal grains; axial columnar in the center; columnar grains grew approximately vertical to the boundary of melt pool. Correlations were investigated between melt pool shape, solidification parameters and microstructure. The transformation of melt pool morphology was mainly attributed to the change of power density. Solidification parameters were shown to be different under different melt pool morphology. Diverse crystal growth patterns were achieved under different melt pool morphology controlled by power density, showing the feasibility of site-specific of microstructure control in DED-L according to the required mechanical properties.

Micro selective laser melting of SS316L: Single Tracks, Defects, microstructures and Thermal/Mechanical properties

With the rapid development of physical science, medical, automotive, biotechnology, energy, communication and optical fields, the demand for micro manufacturing technology is increasing. Micro selective laser melting (MSLM) is advantageous in forming precision and micro manufacturing parts because of its small spot diameter, fine powder and small layer thickness. In this paper, the surface morphology and geometric characteristics of the single tracks were studied and analyzed. The optimization of process parameters by orthogonal tests on the density, surface roughness, microstructure, microhardness and tensile strength were studied and analyzed. Besides, the effect of heat treatment on the organization of the alloy was studied, and tensile experiment and fracture morphology observations were carried out. It is shown that the laser power and scanning speed have a significant effect on the continuity of single tracks forming, and the width of the molten pool is (55 ± 5)μm. A process windows for “Scanning speed-Hatch spacing” was determined, which was divided into four zones: discontinuous, continuous butunstable, continuous stable, excessive melting and unstable. The orthogonal experiment was used to obtain the optimal process parameters. The density of the part was 99.79 ± 0.1%, the surface roughness Ra of the X-Y plane was 2.53 ± 0.3μm, and the Vickers hardness was 209 ± 2.4 HV. After heat treatment, residual stress relief and dissolution of segregation compounds resulted in grain refinement, uniform organization and better mechanical properties. After SRAT + ST, the tensile strength was 499 ± 4.3 MPa, the elongation was 50 ± 1.88%, and the hardness was176 ± 2.0 HV. The tensile fracture dimples are uniformly distributed in size and show equiaxial dimples morphology.

Laser-based powder bed fusion additive manufacturing of pure copper

In this article, the laser-based powder bed fusion (L-PBF) processing behavior of pure copper powder is evaluated by employing a conventional infrared fiber laser with a wavelength of 1080 nm, a small focal spot diameter of 37.5 µm, and power levels up to 500 W. It is shown that bulk solid copper parts with near full density (ρ Archimedes = 99.3 ± 0.2%, ρ Optical = 99.8 ± 0.1%) can be produced using a laser power of 500 W for the chosen combination of powder particle size, L-PBF settings, and pure copper baseplate. Moreover, at 500 W, parts with a relative density exceeding 99% are manufactured within a volumetric energy density window of 230–310 J/mm3, while laser power levels below 500 W did not produce parts with a relative density above 99%. An analytical model is used to elucidate the L-PBF processing behavior, wherein both conduction and keyhole regimes corresponding to the employed L-PBF settings are identified. The analytical model-based results predict that the bulk solid copper parts with near full density are produced in a keyhole regime prior to the onset of keyhole-induced porosity, which is in accordance with the porosity types observed in the parts. The L-PBF fabricated copper parts exhibit an electrical conductivity of 94 ± 1% compared to the international annealed copper standard (IACS) and demonstrate a tensile strength of 211 ± 4 MPa, a yield strength of 122 ± 1 MPa, and an elongation at break of 43 ± 3% in the as-built condition.

Experiments with Femtosecond Laser on Monocrystalline Silicon

Abstract Experiments were performed with femtosecond laser on monocrystalline silicon for different application fields. The small focal spot diameter, the ultra-short pulse length, and the high energy density opens new ways in material processing; the treated material will have smaller heat affected zone (HAZ), and allow more precise, higher quality material processing. Micropillars and LIPSS structures were prepared on monocrystalline silicon in our study.

Improvement in the Analytical Capabilities of LA-ICP-MS for High Spatial Resolution U-Pb Dating of Zircon Using Mixed-Gas Plasma

In this work, a novel method for high spatial resolution U-Pb dating of zircon by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) at 10–16 μm spot diameter has been proposed. This was achieved by introducing 2% (v/v) water-ethanol vapours into ICP in combination with the shielded torch system to increase the sensitivity and suppress the isotopic fractionation effect. Precise and accurate concordant U-Pb ages for Plešovice, GJ-1, and 91500 zircons were obtained using the proposed method, and the results agreed well with the isotope dilution-thermal ionization mass spectrometry (ID-TIMS) and LA-ICP-MS within 2σ, except for the ages obtained using dry plasma at 10 μm spot diameter. Additionally, the effects of plasma condition (dry plasma or 2% (v/v) ethanol plasma) and spot size (10, 16, 24, or 32 μm) on precision (RSD), accuracy (RE), and uncertainty (2σ) of the 206Pb/238U ages have been studied. The results indicated that increasing the spot diameter and introducing 2% (v/v) water-ethanol vapours into ICP significantly improved the precision, accuracy, and uncertainty for small spot diameters (10 and 16 μm), while it exhibited little influence for intermediate spot diameters (24 and 32 μm). Furthermore, the effects of spot size and plasma condition on the precision, accuracy, and uncertainty strongly depended on the sensitivity of analytes.

Processing of Keyhole Depth Measurement Data during Laser Beam Micro Welding

Analysing the quality of weld seams is still a challenging task. An optical inspection of the surface is giving limited information about the shape and depth of the weld seam. An application for laser beam welding with high demands regarding the weld depth consistency is the electrical contacting of battery cells. The batteries themselves have a limited terminal or case thickness that must not be penetrated during the welding process to avoid leakage or damage to the cell. That leads to a minimum weld depth to ensure the electrical functionality, and a maximum weld depth indicated by the case thickness. In such applications, a destructive analysis is not suitable which leads to the demand for a non-destructive measurement during the process. Using a coaxial, interferometric measurement setup, the keyhole depth during the deep penetration welding is measureable. For a keyhole with a depth of a couple of millimetres, such a system is commercially available. In micro scale, however, these systems are facing several challenges such as scanning systems, small spot diameters of a few tens of micrometres and narrow keyholes. This study contains an investigation of an interferometric measurement of the keyhole depth and the suitability for laser micro welding. Therefore, the data processing of the achieved measurements is investigated, and the results are compared with the depth measurement of metallographic analysed samples. Stainless steel is used to investigate the behaviour and the stability of developed data processing strategy and the resulting depth values.

Effect of pulsed laser parameters on deformation inhomogeneity in laser shock incremental forming of pure copper foil

The dependence of deformation inhomogeneity on the pulsed laser parameters in laser shock incremental forming (LSIF) of pure copper foil was studied based on finite element simulation. The formed depth, angle, profile and limiting fluctuation value were adopted to evaluate the forming deviation of parts. The digital microscope was employed to examine the bottom surface morphology of formed parts. The effect of pulsed laser energy, spot diameter and overlapping rate on the deformation inhomogeneity in LSIF was investigated. It is revealed that there are variances in the shape and dimension of formed parts along both the shock and travelling directions owing to the local loading history of LSIF. The formed depth and angle are different in various positions of formed parts along the shock direction, while the formed profile presents a periodic variation along the travelling direction. The appropriate enhancement of laser energy can improve the deformation inhomogeneity along both the shock and travelling directions. The deformation profiles along the shock and travelling directions depend on the adopted spot diameter. The rebound effect may occur while too small spot diameter is employed, resulting in the degradation of forming accuracy. The overlapping rate has a major impact on the surface morphology of formed parts. As the overlapping rate increases to 80%, the limiting fluctuation values along the travelling direction become large due to the distortion at the free end. Under the given process conditions, the laser energy of 1100 mJ, the spot diameter of 2.5 mm and the overlapping rate of 60% are recommended to achieve straight-line channels with high forming quality.

Enhancing Hardness and Wear Performance of Laser Additive Manufactured Ti6Al4V Alloy Through Achieving Ultrafine Microstructure.

Refining microstructure is an important issue for laser additive manufacturing (LAM) of titanium alloy. In the present work, the microstructures of LAM-fabricated Ti6Al4V alloy were refined using a low energy density with the combination of a small spot diameter, a low laser power, and a high scanning speed. The microstructure, hardness, wear performance, and molten pool thermal behavior of LAM-fabricated Ti6Al4V coatings were studied. The results show that the grain sizes of both prior β and α phases are strongly dependent on the cooling rate of the molten pool. The fine prior β grains and submicron-scale acicular α phases were obtained under a low energy density of 75 J mm−2 due to the high cooling rate of the molten pool. In addition, the as-fabricated Ti6Al4V sample with submicron-scale acicular α phase showed a very high hardness of 7.43 GPa, a high elastic modulus of 133.6 GPa, and a low coefficient of friction of 0.48. This work provides a good method for improving the microstructure and mechanical performance of LAM-fabricated Ti6Al4V alloy.

Experimental analysis of zero-gap laser welding of zinccoated steels in a lap joint configuration

Automotive manufacturing requires high productive manufacturing technologies to ensure a high-volume efficient production. Joining metal sheets in an overlap joint configuration of zinc-coated steel is an important task for body-in-white production. This paper describes the influence of different spot sizes regarding process stability in laser beam welding. Therefore, welds were performed in an overlap joint configuration with fully penetrated welds. Relevant material combinations for automotive industry were investigated. A broad-based parameter study and the analysis of interaction between spot- and keyhole diameter state a higher process stability. Welds with a smaller spot diameter lead to a sufficient increase of joint quality by using a zero gap overlap configuration. It is shown that the amount of joint instabilities such as pores, pinholes, spatter and further defects can be minimized by using smaller spot diameters. This can be explained by different keyhole regimes. Moreover, the change of isothermal interaction in the interlayer zone caused by the adjusted spot diameter leads to high-quality joints.

Laser welding of laser-structured copper connectors for battery applications and power electronics

The electrification of the automobile industry leads to an increasing demand for high-performance energy storage systems. The more complex the battery pack, the more complex the electronic components will become. Very high currents have to be transported in a short time and very fast electrical switching processes have to be made possible. These requirements have an effect on the required quality of the electrical connection. Furthermore, a joining process is required that offers short cycle times and a high degree of automation. Laser micro welding with fibre lasers (1070 nm) meets the requirements placed on joining technology. Due to the high beam quality, very small spot diameters and thus very high intensities can be achieved. Copper materials of high purity are used to achieve the high conductivity of the electrical connection. This material, in turn, poses a great challenge to the welding process, since the reflectance for the beam sources mentioned is above 95%.This paper presents a way of significantly reducing the reflectance for copper connectors and thus making the joining process more efficient. For this purpose, the copper connectors are first pre-processed with an ultrashort pulse laser process, which significantly increases the surface area. In a second step, bead-on-plate welds are carried out on the structured surfaces and the absorption coefficient is determined during the welding process with the aid of a double integrating sphere assembly in comparison to a bare copper sample.

Simulation of laser-driven cratering experiments on aluminum

After a brief description of the physical principles involved in the cratering process, the authors present a specific methodology to simulate laser-driven cratering experiments performed with a long pulse duration (100 ns) and a small focal spot diameter (220μm). This methodology can be divided into two steps. First, the 2D-axisymmetrical pressure field generated by the laser on the target is determined from laser parameters. Second, this pressure is applied on the surface of the target in a Eulerian simulation. In order to validate this methodology, the authors simulate a laser shot on a thin aluminum target whose rear surface velocity is recorded by a VISAR (Velocity Interferometer System for Any Reflector). Once validated, they use the methodology to simulate laser-driven cratering experiments on semi-infinite aluminum targets. Numerical results are compared to experimental measurements of the craters. Although slight differences are pointed out and discussed, the proposed methodology is well adapted to simulate craterization laser shots.

Electrical resistivity of pure copper processed by medium-powered laser powder bed fusion additive manufacturing for use in electromagnetic applications

Pure copper is an excellent thermal and electrical conductor, however, attempts to process it with additive manufacturing (AM) technologies have seen various levels of success. While electron beam melting (EBM) has successfully processed pure copper to high densities, laser powder bed fusion (LPBF) has had difficulties achieving the same results without the use of very high power lasers. This requirement has hampered the exploration of using LPBF with pure copper as most machines are equipped with lasers that have low to medium laser power densities. In this work, experiments were conducted to process pure copper with a 200 W LPBF machine with a small laser spot diameter resulting in an above average laser power density in order to maximise density and achieve low electrical resistivity. The effects of initial build orientation and post heat treatment were also investigated to explore their influence on electrical resistivity. It was found that despite issues with high porosity, heat treated specimens had a lower electrical resistivity than other common AM materials such as the aluminium alloy AlSi10Mg. By conducting these tests, it was found that despite having approximately double the resistivity of commercially pure copper, the resistivity was sufficiently low enough to demonstrate the potential to use AM to process copper suitable for electrical applications.

Two-dimensional axisymmetric opto-thermal phosphor modeling based on fluorescent radiative transfer equation

Remote phosphor plate excited by the light-emitting diode (LED) or laser diode (LD) has been widely applied in solid-state lighting. The light propagation properties within the phosphor have been analytically characterized based on the one-dimensional assumption. However, this may be not feasible in some cases, e.g., the excitation spot diameter is comparable to the plate thickness or the incident irradiance is not uniform along the horizontal direction. In this work, we extend the one-dimensional model to a two-dimensional axisymmetric opto-thermal model based on the fluorescent radiative transfer equations (FRTEs) for the cylindrical phosphor plate excited by a collimated beam with a small spot diameter and Gaussian irradiance distribution. The radiances of the blue and yellow lights are iteratively calculated by solving FRTEs in the cylindrical coordinate system using the discontinuous spectral element method. By inputting the obtained heat generation density from FRTEs, we calculate the three-dimensional temperature distribution by solving the heat diffusion equation (HDE). In addition, the opto-thermal interaction between FRTEs and HDE is achieved by introducing the temperature-dependent phosphor quantum efficiency. Using the model, we evaluate the optical, thermal and opto-thermal interacted performances of the phosphor. Finally, the model is validated by comparing the measured output optical power and surface temperature distribution with the calculated results.

Diffusing, Side-Firing, and Radial Delivery Laser Balloon Catheters for Creating Subsurface Thermal Lesions in Tissue.

Infrared lasers have been used in combination with applied cooling methods to preserve superficial skin layers during cosmetic surgery. Similarly, combined laser irradiation and tissue cooling may also allow development of minimally invasive laser therapies beyond dermatology. This study compares diffusing, side-firing, and radial delivery laser balloon catheter designs for creation of subsurface lesions in tissue, ex vivo, using a near-IR laser and applied contact cooling. An Ytterbium fiber laser with 1075 nm wavelength delivered energy through custom built 18 Fr (6-mm-OD) balloon catheters incorporating either 10-mm-long diffusing fiber tip, 90 degree side-firing fiber, or radial delivery cone mirror, through a central lumen. A chilled solution was flowed through a separate lumen into 9-mm-diameter balloon to keep probe cooled at 7°C. Porcine liver tissue samples were used as preliminary tissue model for immediate observation of thermal lesion creation. The diffusing fiber produced subsurface thermal lesions measuring 49.3 ± 10.0 mm2 and preserved 0.8 ± 0.1 mm of surface tissue. The side-firing fiber produced subsurface thermal lesions of 2.4 ± 0.9 mm2 diameter and preserved 0.5 ± 0.1 mm of surface tissue. The radial delivery probe assembly failed to produce subsurface thermal lesions, presumably due to the small effective spot diameter at the tissue surface, which limited optical penetration depth. Optimal laser power and irradiation time measured 15 W and 100 s for diffusing fiber and 1.4 W and 20 s, for side-firing fiber, respectively. Diffusing and side-firing laser balloon catheter designs provided subsurface thermal lesions in tissue. However, the divergent laser beam in both designs limited the ability to preserve a thicker layer of tissue surface. Further optimization of laser and cooling parameters may be necessary to preserve thicker surface tissue layers.

Simple method for manufacturing and optical characterization of tapered optical fibres

AbstractPhotonic devices often use light delivered by a single-mode telecommunication fibre. However, as the diameter of the core of the optical fibre is of 10 microns, and the transverse dimensions of the photonic waveguides are usually micrometer or less, there is an issue of incompatibility. The problem may be solved by application of tapered optical fibres. For efficient light coupling, the taper should be prepared so as to create a beam of long focal length and small spot diameter in the focus. The article describes the design, fabrication and characterization of tapered optical fibres prepared with a fibre-optic fusion splicer. We modelled the tapers with FDTD method, for estimation of the influence of the tapered length and angle on the spot diameter and the focal length of an outgoing beam. We fabricated tapers from a standard single mode fibre by the Ericsson 995 PMfi- bre-optic fusion splicer. We planned the splicing technology so as to get the needed features of the beam. We planned a multistep fusion process, with optimized fusion current and fusion time. The experimental measurements of best tapered optical fibres were carried out by the knife-edge method.

Accuracy of Three-Dimensional Shape Measurement Using a Triangulation Method Sensor with Optical Skid

On-machine measurement is used in ultra-processing machining, but it is seldom used in precision machining. For on-machine measurement, it is necessary that the sensor not be easily affected by the moving error or environment vibration in the field of precision machining. A triangulation method sensor with the optical skid method made using a new design concept is proposed to remove the moving error and vibration. The optical skid method used two laser spots with different sizes: the small spot diameter is the stylus and the large spot diameter is the skid [1]. The difference between these two signals reflects the surface shape. The developed sensor comprises an optical source and two optical receiving systems. Each optical receiving system has an imaging lens and a detector. Instead of two laser spots of different sizes, two detectors with different sizes of receiving area serve as the optical skid. Results confirmed the possibility of reducing the influence of the vibration using the developed sensor. In on-machine measurements, measurement of the surface profile with long wavelength is often necessary. If the spot diameter of the skid is not much larger than the surface profile wavelength, then the smoothing effect of the skid is reduced. Therefore, the amplitude of the measured profile by the skid sensor is smaller than actual amplitude of the workpiece. This paper presents a method of reconstructing the surface profile from the measurement results and the obtained effects of the reconstruction method from simulations and experiments.

Development of laser beam welding for the lip seal configuration

A vacuum seal using the lip sealing technique is emerging as the most likely choice for fusion devices, to comply with the requirement of maintainability. The welding technology considered for lip sealing is laser welding, due to the attributes of small spot diameter, low concentrated heat input, high precision and penetration. To establish the process, an experiment has been conducted on a sample size of 150mm×50mm having thickness of 2mm, material AISI304L to assess the dependence of beam parameters like, laser power, speed and focusing distance on penetration and quality of weld joint. Further, the assessment of the effect of welding set-up variables like air-gap between plates, plate misalignment, and laser beam misalignment on the weld quality is also required. This paper presents the results of this experimental study and also the plan for developing a large (∼10m) size laser welded seal, that simulates, appropriately, the configuration required in large dimension fusion devices.

In-Well Pumped Blue GaN-Based Vertical-External-Cavity Surface-Emitting Lasers

We describe the properties of in-well pumped blue InGaN/GaN vertical-external-cavity surface-emitting lasers. The laser hetero-structures were deposited on bulk GaN substrates by using metal–organic vapor phase epitaxy near atmospheric pressure. The active zones are comprised of up to 20 InGaN quantum wells distributed in a resonant periodic gain configuration. High-reflectivity dielectric distributed Bragg-reflectors were used as mirrors. Lasing was achieved at a wavelength of about 440–445 nm by exclusively exciting the quantum wells with the 384 nm emission line of a dye/N2 laser. The laser threshold was about 240 kW/cm2. The small pump spot diameter of about 20 µm and the usage of dielectric mirrors result in a rather high thermal resistance, which was experimentally determined by using an all optical measurement technique based on the temperature-dependent change of the refractive index of the device.