Laser Beam Diameter Research Articles

Semi-Analytical Solution for Modelling Moving Heat Sources in a Semi-Infinite Medium with Radiative and Convective Boundary Conditions

The weld quality is highly related to the thermal history of the weld and there have been many trials to monitor the quality using an infrared (IR) sensor. To obtain the real temperature of a surface based on the brightness temperature values measured by an IR camera, the emissivity value must be derived. For an accurate assessment of the emissivity, one must be aware of the melting point isotherm. The temperature profiles only depend on three factors during laser processing, specified as constants the characteristics of the material: laser beam speed (v), laser beam diameter (d), and power (P). Predicting the width of the melted zone reached during the welding process as the parameters vary is a tool for helping a quality laser processing and for determination of true temperature in laser welding using IR camera. This study describes the semi-analytical (SA) solution of the heat conduction equation for a localized moving Gaussian heat source with constant parameters on a semi-infinite medium. The solution, simple and quick to obtain, provides information on the width of the melted zone with an average error < 5 %. The outcome is assessed numerically and contrasted with FEM solutions for a Gaussian source, the latter having undergone experimental validation. With two distinct defocus values, def0 and def-6, and by varying the speed and power settings, two separate types of experiments were run. Thus, the SA solution was obtained and compared after the FEM solution had been obtained with a good approximation (max err 4.3 %, average err 2.7 %). Only in regard to the 1AL test is an error more than 5 % detected; in the other case, the average error is 3.75 %. Two more tests at the defocus values of def-4 and def-8 were conducted to confirm the model's validity as the parameters varied. Overall, the average error between the semi-analytical and the FEM solution is 4.1%. The SA solution may be used to effectively estimate the isotherms related to the melting point of aluminum (770 K). This allows to obtain a tool which helps restoring the real temperature based on the brightness values measured by the IR camera during laser welding. At the same time, this effective tool allows to investigate the importance of different processing parameters in laser manufacturing.

Formation and Characterization of MgSe Alloys by Pulsed Laser Welding Technique

AbstractHerein, MgSe alloys with different compositions are fabricated using laser welding techniques within a couple of minutes in an argon atmosphere. The optimum laser welding parameters, which reveal the correct compositional ratios, are determined by varying arc voltage, pulse width, welding frequency, and laser beam diameter. The structure of the MgSe alloy is monoclinic. Additionally, scanning electron microscopy studies have shown that MgSe alloys are least porous and have a layered structure. The electrical resistance of the welded alloys depends on the Mg content in the samples. Measurements from impedance spectroscopy have shown that the alloys can function as band filters, displaying cutoff frequency values of ≈16 GHz for AC signals propagating at a driving frequency of 1.0 GHz with an amplitude of 0.10 V. The properties of the MgSe alloys make them attractive for use in 5G/6G technology applications as band filters.

Noise analysis of the atomic superheterodyne receiver based on flat-top laser beams.

Since its theoretical sensitivity is limited by quantum noise, radio wave sensing based on Rydberg atoms has the potential to replace its traditional counterparts with higher sensitivity and has developed rapidly in recent years. However, as the most sensitive atomic radio wave sensor, the atomic superheterodyne receiver lacks a detailed noise analysis to pave its way to achieve theoretical sensitivity. In this work, we quantitatively study the noise power spectrum of the atomic receiver versus the number of atoms, where the number of atoms is precisely controlled by changing the diameters of flat-top excitation laser beams. The results show that under the experimental conditions that the diameters of excitation beams are less than or equal to 2 mm and the read-out frequency is larger than 70 kHz, the sensitivity of the atomic receiver is limited only by the quantum noise and, in the other conditions, limited by classical noise. However, the experimental quantum-projection-noise-limited sensitivity this atomic receiver reaches is far from the theoretical sensitivity. This is because all atoms involved in light-atom interaction will contribute to noise, but only a fraction of them participating in the radio wave transition can provide valuable signals. At the same time, the calculation of the theoretical sensitivity considers both the noise and signal are contributed by the same amount of atoms. This work is essential in making the sensitivity of the atomic receiver reach its ultimate limit and is significant in quantum precision measurement.

Developing a Support Vector Regression (SVR) Model for Prediction of Main and Lateral Bending Angles in Laser Tube Bending Process.

The laser tube bending process (LTBP) is a new and powerful manufacturing method for bending tubes more accurately and economically by eliminating the bending die. The irradiated laser beam creates a local plastic deformation area, and the bending of the tube occurs depending on the magnitude of the heat absorbed by the tube and its material characteristics. The main bending angle and lateral bending angle are the output variables of the LTBP. In this study, the output variables are predicted by support vector regression (SVR) modeling, which is an effective methodology in machine learning. The SVR input data is provided by performing 92 experimental tests determined by the design of the experimental techniques. The measurement results are divided into two sub-datasets: 70% for the training dataset, and 30% for the testing dataset. The inputs of the SVR model are process parameters, which can be listed as the laser power, laser beam diameter, scanning speed, irradiation length, irradiation scheme, and the number of irradiations. Two SVR models are developed for the prediction of the output variables separately. The SVR predictor achieved a mean absolute error of 0.021/0.003, a mean absolute percentage error of 1.485/1.849, a root mean square error of 0.039/0.005, and a determination factor of 93.5/90.8% for the main/lateral bending angle. Accordingly, the SVR models prove the possibility of applying SVR to the prediction of the main bending angle and lateral bending angle in LTBP with quite an acceptable accuracy.

Comparing mobile and terrestrial laser scanning for measuring and modelling tree stem taper

Abstract Measuring and modelling the shape of tree stems is a fundamental component of forest inventory systems for both commercial and biological purposes. The change in diameter of the stem along its length (a.k.a. 'taper') is one of the most important and widely used means of predicting tree stem volume. Until recently, the options for obtaining accurate estimates of stem taper and developing stem taper models have been limited to measurements of felled trees or the use of optical dendrometers on standing live trees. Here, we tested both a tripod-mounted terrestrial laser scanner (TLS; a Focus 3D 120 of FARO Technologies, Inc., Lake Mary, FL, USA), and a mobile laser scanner (MLS; the ZEB1 of the GeoSLAM Ltd, Nottingham, UK) to measure tree diameters at various heights along the stem of 20 destructively harvested broadleaf and needleleaf species using the outer hull modelling method, for the purpose of developing individual-tree and species-specific taper models. Laser scanner specifications were a major factor determining stem taper measurement accuracy. The longer-range, low beam divergence TLS could estimate stem diameter to an average of 15.7 m above ground (about 79 per cent of the canopy height), while the shorter-range high beam divergence MLS could estimate an average of 11.5 m above ground (about 45 per cent of the canopy height). Stem taper error increased with respect to height above ground, with the TLS providing more consistent and reliable diameter measurements (root mean square error (RMSE) = 1.93 cm; 9.57 per cent) compared with the MLS (RMSE = 2.59 cm; 12.84 per cent), but both methods were nearly unbiased. We attribute ~60 per cent of the uncertainty in stem measurements to laser beam diameter and point density, showing positive and negative correlations, respectively. MLS was unable to converge on the two tested taper models but was found to be an efficient means of easily sampling diameters at breast height (DBH) and reconstructing stem maps in simple forest stands with trees greater than ~10 cm DBH. TLS provided precision stem diameter measurements that allowed for the creation of similar taper models for three out of the four study species. Future work should focus on evaluating MLS systems with improved specifications (e.g. beam divergence and range), since these instruments will likely lead to dramatic improvements in reliable estimates of forest inventory parameters, in line with the current TLS technology.

Microstructure evolution and vacuum tribological properties of surface nitriding layer on a TiZrAlV alloy fabricated by laser nitriding

The evolution mechanisms of phase, microstructure and vacuum tribological properties for Ti–20Zr-6.5Al–4V under different laser beam diameters have been investigated by using laser surface nitriding (LSN). Results indicate that all the LSN samples are mainly composed of α phase and Ti(Zr)N phase, besides, Ti(Zr)N0.3 phase can also be obtained, which is based on a change in the ratio of liquefied nTi(Zr)/nN. With the laser beam diameter decreasing from 3 to 1 mm, the thickness and density of nitride layer increase significantly, which contribute to the increased energy input density. EPMA results indicate that the nitrides mainly exist in the form of Ti(Zr)xNy, and the distribution transformation of Al and V elements has also been analyzed. As the laser beam diameter decreases, the coefficient of friction decreases, and the sample with 1 mm laser beam diameter display the lowest coefficient of friction (∼0.333). Also, the wear volume and wear rate of the LSN sample with 1 mm laser beam diameter are the smallest, which are both reduced by about 40% compared with the original sample. After analysis, the wear pattern of the LSN samples can be confirmed as the composite of adhesive wear and abrasive wear. Nitride dendrites can form a support skeleton between the wear surface and friction pair, which can significantly reduce the wear of LSN sample surface. The results of this work prove the feasibility of improving the surface wear resistance of Ti–20Zr-6.5Al–4V by LSN.

Experimental evaluation of cut quality and temperature field in fiber laser cutting of AZ31B magnesium alloy using response surface methodology

Fiber laser cutting of AZ31B magnesium alloy was studied to assess the effect of laser cutting process parameters on the resultant cutting temperature near the cut kerf and the resultant cut quality. To systematically analyze the effect of parameters on the temperature variation and cutting edge surface roughness during the cutting process of the AZ31B magnesium alloy, the Response Surface Methodology (RSM) was utilized to fit a quadratic polynomial model through the experiments. The influence of three main factors including speed of cutting, power of laser and nozzle distance on the major responses of temperature near the cut kerf, average surface roughness of the cutting edge and the cut kerf quality was then evaluated.Changes in the cutting speed had no serious impact on the quality of the cut kerf.Laser power levels from 800 to 1000 W were suitable for laser cutting of magnesium alloy sheets. The results showed thatvariations in the nozzle distance and laser emitted power had a remarkable effect on the temperature variation around the cut kerf width. Changing the nozzle distance and thereby creating different laser beam diameter had a more significant influence on the temperature variation rate (about 15 %), in comparison to the laser power. The nozzle distance had a huge effect on the cutting edge surface roughness due to the significant variation of laser beam energy density and beam diameter and hence, the cut kerf dimensional changes.The optimal cutting condition was obtained at the minimum roughness according to the investigated parameters levels, which included the cutting speed of 6 m/min, the power level of 1000 W and the nozzle distance of 0.8 mm. The SEM images from the top surface of the cut kerf implied the existence of oxidation in the magnesium alloy kerf edges.

Keyhole-in-keyhole formation by adding a coaxially superimposed single-mode laser beam in disk laser deep penetration welding

Laser deep penetration welding is characterized by the formation of a vapor capillary (keyhole) and a high overall absorption (coupling rate) of the laser radiation in comparison to heat conduction welding. Due to multiple reflexions within the highly dynamic keyhole, the absorption mechanisms are very complex. The questions, how a laser beam interacts with the existing keyhole, and, if shadowing effects occur, are a matter of concern for several researchers. In this study, the hypothesis that the beam of a laser source can be transmitted to a significant extent through an existing keyhole and acts predominantly at the keyhole bottom was investigated. Experiments were carried out on mild steel and technical pure aluminum, using a specially designed optical system, which allows to coaxially combine two laser beams and to adjust their settings like the energy and the focal plane individually. A combination of a disk laser with a focal diameter of 390 µm and a single-mode fiber laser with a focal diameter of 30 µm was used. Weld depths and seam shapes were analyzed in cross and longitudinal sections. Based on the results, it is shown that the much smaller focal diameter of the single-mode laser beam acted at the bottom of the keyhole and caused a kind of “keyhole-in-keyhole formation” in the form of a local maximum in weld depth whose expression depended on the focal plane of the single-mode laser beam.

Argon laser trabeculoplasty for congenital ectropion uveae: Case report and review of the literature.

A 18-year-old woman with unilateral glaucoma secondary to congenital ectropion uveae (CEU) in the right eye, without other systemic and ocular associations. Intraocular pressure (IOP) was uncontrolled under topical therapy. The visual field (VF) was within normal limits; retinal nerve fiber layer (RNFL) thickness, as evaluated by Optical Coherence Tomography (OCT), was reduced. The patient refused surgical intervention. After evaluation of the iridocorneal angle, ALT was performed as follows: 95 spots were applied for the 270 ° of visible trabecular meshwork using a laser beam diameter of 50 μm, an exposure time of 0.1 s and a power of 750 mw). Mean IOP in the right eye, as evaluated by diurnal tonometric curve, was 10 mmHg, 16 mmHg and 20 mmHg respectively one month, four months and eight months after ALT, with no additional topical therapy, and 18 mmHg twelve months after ALT with topical therapy. CEU is a rare, non-progressive anomaly characterized by the proliferation of iris pigment epithelium on anterior surface of iris; glaucoma, in this disorder, is often poorly controlled with medical therapy alone. In a phase of initial glaucomatous damage and with a not particularly high IOP, as in this case, ALT could be an alternative therapeutic option at least in the short-term, when surgery is not feasible immediately. In fact, given its limited effectiveness over time, ALT can be used as a temporary control measure of IOP, pending surgery to become feasible.

Measurement of Spot Diameter and Divergence of Laser Beam by Shadow Method Using Generalized Parameters

Measurement of Spot Diameter and Divergence of Laser Beam by Shadow Method Using Generalized Parameters

Electrically tunable conducting oxide metasurfaces for high power applications

Abstract Active metasurfaces designed to operate at optical frequencies are flat optical elements that can dynamic, subwavelength-scale wavefront control of reflected or transmitted light. The practical and fundamental power-handling limits of active metasurfaces at high pulse energies and high average powers determine the potential applications for these emerging photonic components. Here, we investigate thermal performance limits of reflective gate-tunable conducting oxide metasurfaces illuminated with high power density laser beams, for both continuous wave (CW) and pulsed laser illumination. Our gate-tunable metasurfaces use indium tin oxide (ITO) as an active material, which undergoes an epsilon-near-zero (ENZ) transition under applied electrical bias. We experimentally show that under CW illumination, there is no significant change in the electrically tunable metasurface optical response for high irradiances ranging from 1.6 kW/cm2 to 9.1 kW/cm2 when the illuminating laser beam diameter is 7 μm. Even under an applied bias, when over 60% of the incoming light is absorbed in a 1 nm–thick charge accumulation layer within ITO, the local temperature rise in the metasurface is modest, supporting its robustness for high-power applications. Additionally, we theoretically show that in the ENZ regime, the metasurface reflectance can be increased by a factor of 10 by replacing the active ITO layer with cadmium oxide (CdO). Thus conducting oxide metasurfaces can tolerate the power densities needed in higher power applications, including free space optical communications, to light detection and ranging (LiDAR), as well as laser-based additive manufacturing.

Finite element analysis of deformation behaviour of circular sheet during laser forming process

Laser forming of sheet metal involves inducing a bending process through the application of thermal stress using a defocused laser source. In laser forming the formation of bowl-shaped shapes requires the input of various laser process parameters. In this study, we investigate the thermo-mechanical deformation behaviour of a circular plate subjected to laser irradiation scanning. To analyse this phenomenon, we employ the Finite Element Method (FEM) with the aid of the software ABAQUS 6.10. The moving laser heat source is modelled as Gaussian heat flux, and DFLUX subroutine is written in FORTRAN. The work piece material AH36 is considered. The Finite Element Method (FEM) proposed model is verified against experimental results. Additionally, a parametric study has been conducted to assess the impact of laser process parameters on the temperature distribution of AH 36 material. The temperature distribution is noted to rise with an increase in laser power. However, as the scanning speed and laser beam diameter of the circular laser heat source increase, both temperature and bend angle exhibit a continuous decrease. Further, it is found the plastic strain is measured along the laser irradiation path, therefore the averaged material properties are not altered of the dome shaped obtained by laser forming. Based on the parametric studies, the optimum laser process parameters are also determined to get the dome shaped of the circular sheet.

Experimental study on laser propagation characteristics in local air turbulence disturbed by coherent acoustic waves

The existence of atmospheric turbulence seriously restricts the application of laser technology. However, the acoustic wave will affect the air density during the propagation process, change the original structure of the air turbulence, and then affect the propagation of the laser in the air turbulence. To study the effect of disturbance of atmospheric turbulence by acoustic waves on laser propagation, the propagation characteristics of lasers in local atmospheric turbulence under coherent acoustic wave perturbation are investigated experimentally. First, a coherent acoustic wave generator and a closed local air turbulence simulation device are designed. The propagation experiments of laser in a closed local air turbulence environment disturbed by coherent acoustic waves are carried out. It is found that the coherent acoustic wave will interfere with the wave reflected from the inner wall of the closed local air turbulence simulation device, and the sound pressure forms a regular standing wave intensity distribution pattern. Moreover, the variations of laser beam drift fluctuation variance, scintillation index, and beam diameter with coherent acoustic wave frequency, power, and sound source array position are studied. The results show that the original structure of air turbulence will be changed in the process of coherent acoustic wave propagation, which will affect the beam drift fluctuation variance, scintillation index, and beam diameter changes of laser propagation in air turbulence. The beam drift fluctuation variance, scintillation index, and beam diameter change regularly with the change of the frequency and power of the sound source. Changes of the fluctuations with frequency are relatively gentle, whereas changes with power are severe. This paper explores the influence of coherent acoustic waves disturbing air turbulence on laser propagation characteristics, and the research results provide a basis for improving or disturbing laser propagation performance in atmospheric turbulent environments.

Realising high aspect ratio 10 nm feature size in laser materials processing in air at 800 nm wavelength in the far-field by creating a high purity longitudinal light field at focus

In semiconductor and data storage device manufacturing, it is desirable to produce feature sizes less than 30 nm with a high depth-to-width aspect ratio on the target material rapidly at a low cost. However, optical diffraction limits the smallest focused laser beam diameter to around half of the laser wavelength (λ/2). The existing approach to achieving nanoscale fabrication is mainly based on costly extreme ultraviolet (EUV) technology operating within the diffraction limit. In this paper, a new method is shown to achieve materials processing resolution down to 10 nm (λ/80) at an infrared laser wavelength of around 800 nm in the far-field, in air, well beyond the optical diffraction limit. A high-quality longitudinal field with a purity of 94.7% is generated to realise this super-resolution. Both experiments and theoretical modelling have been carried out to verify and understand the findings. The ablation craters induced on polished silicon, copper, and sapphire are compared for different types of light fields. Holes of 10–30 nm in diameter are produced on sapphire with a depth-to-width aspect ratio of over 16 and a zero taper with a single pulse at 100–120 nJ pulse energy. Such high aspect ratio sub-50 nm holes produced with single pulse laser irradiation are rarely seen in laser processing, indicating a new material removal mechanism with the longitudinal field. The working distance (lens to target) is around 170 µm, thus the material processing is in the far field. Tapered nano-holes can also be produced by adjusting the lens to the target distance.

Reflection Coefficient Estimation of Femtosecond Laser Surface Processing Using Support Vector Regression

An image analysis-based Reflection Coefficient (RC) estimation method of femtosecond laser surface processing for the blackening of X-ray imaging sensor shell is proposed. The Support Vector Regression (SVR) is used for RC computation and both an offline and an online steps are considered in this method. Regarding offline step, the typical laser process parameters are set to perform surface processing and Scanning Electron Microscope (SEM) images are recorded. Then a series of image features are computed and both the computed image features and typical laser parameters are used to train SVR: the training dataset includes the laser line space, laser beam diameter, natural logarithm of laser power divided by laser frequency, and image features of Gray-Level Co-occurrence Matrix (GLCM); the supervising data are laser ablation diameters. As for online step, when SEM image data are recorded after laser processing, the trained SVR is used to predict laser ablation diameter and then the RC can be computed by laser ablation model. Many experiment results have verified the effectiveness of our proposed method, and the RC estimation accuracy can be better than 90.0%.

Analysis of optimal detection range performance of LiDAR systems applying coaxial optics

In this study, the optimal detection range performance of a LiDAR system employing coaxial optics is analyzed. On analyzing laser beam diameter, beam divergence angle, light-receiving area, and receiving light intensity, the optimal detection range was exhibited when the collimator focal length was 6.5 mm, the laser-beam divergence angle was 1.23 mrad, and the hole of the receiving mirror was 1.4 mm. Furthermore, the maximum deviation of the optical scan angles with respect to the mechanical angles of the polygon mirror and the MEMS mirror were analyzed as -0.99° and +4.54° in the x-axis and y-axis directions, respectively.

Investigating the laser metal deposition of Inconel 718 superalloy using the numerical and experimental methods

In this research, a volume of fluid (VOF) model was developed to investigate the effect of laser deposition parameters on the geometry of molten pool and deposited layer in the Inconel 718 superalloy. For this purpose, the process parameters of laser power, laser beam diameter and scanning speed were considered to estimate the geometric characteristics of the molten pool and deposited layer. In the following, the laser deposition process of Inconel 718 superalloy was carried out experimentally to validate the results of simulation. It was observed that an increase in the laser power from 100 to 400 W resulted in an improvement in the length, width and depth of molten pool, while an increase in the values of laser beam diameter (from 1 to 2 mm) and scanning speed (from 2 to 10 mm s−1) was associated with a reduction in the length, width and depth of molten pool. From the results of both simulation and experiments, a reduction was observed in the wetting angle of deposited layer when the values of laser power and scanning speed increased up to 400 W and 10 mm s−1 respectively, while the increase of feeding rate from 48 to 62 mgr s−1 indicated an improvement in the wetting angle. It was also observed that the maximum penetration depth was obtained in the rear part of molten pool due to Marangoni convection currents that pushed the melt toward the end of molten pool. The comparison of the experimental results and those predicted by the VOF model indicated that the model is capable of predicting the shape of deposition layer with sensible error.

Monte-Carlo method based simulations for photothermal mucosa coagulation with accurate depth limits

The mucosa layer, the innermost layer of the gastrointestinal (GI) system, is of great importance in carcinogenesis since most cancerous tissues occur as superficial lesions. Although various treatment strategies exist, the main difficulty in eradicating lesions is unintentional damage to healthy tissues with the uncontrolled depth of treatment. This study proposes a computer modeling approach for simulating depth-resolved photothermal (laser) mucosal coagulation therapy. Computer modeling mimics the thermal dynamics of mucosal tissue to characterize the total heat energy required for successful superficial coagulation, which can be controlled by the scan rate, scan time, output power, and beam diameter of the applied laser. It consists of three steps: 1) Monte Carlo simulation to generate a laser energy distribution profile. 2) Heat transfer simulation to calculate the resulting tissue temperature. 3) Thermal damage estimation based on the calculated dead cell ratio. This computer modeling was performed for a laser wavelength of 1500 nm. Transient temperature profiles and a corresponding thermal damage map were generated as functions of laser scanning speed, power, and beam diameter. The guide map estimates that mucosal coagulation can be achieved with the accurate depth limits at 1500 nm laser wavelength, 1 mm beam diameter, 0.33-0.43 W/cm2 irradiation range, and 1-3 mm/s scanning speeds. This computing approach may hold promise in determining optimal therapy parameters for depth-resolved adequate coagulation in a single session with further development.

Recent Advances in Single-Cell Metabolomics Based on Mass Spectrometry

Recent Advances in Single-Cell Metabolomics Based on Mass Spectrometry

Effect of Laser Beam Diameter on the Microstructure and Hardness of 17-4 PH Stainless Steel Additively Manufactured by Direct Energy Deposition

Effect of Laser Beam Diameter on the Microstructure and Hardness of 17-4 PH Stainless Steel Additively Manufactured by Direct Energy Deposition