Modulation Of Laser Beam Research Articles

Acoustic process monitoring during the laser beam welding of stainless-steel foils using an adjustable ring mode laser beam source

Electrification of the mobility sector is vital to meet the targets for reducing greenhouse gas emissions. Besides battery-based mobility solutions, polymer electrolyte membrane fuel cells (PEMFCs) are a promising technology for electrifying drive trains, especially in heavy-duty applications, such as maritime or logistics. Bipolar plates, a key component of PEMFCs, can consist of two stainless-steel foils that must be welded to be gas-tight. In order to join the two metal foils, laser beam welding is the state-of-the-art technology. Current challenges include process instabilities at higher welding speeds, such as the humping effect, which can cause weld seam imperfections. Therefore, applying sensors for laser beam welding is a promising approach to monitor the welding process. AISI 316L foils were welded within the scope of this work with various process parameters using an adjustable ring mode laser beam source. Additionally, an optical microphone was used as a process monitoring system. By applying different parameter settings and due to the introduction of artificial faults, weld seam defects, such as a burn-through or a gap, were induced. After utilizing a noise reduction algorithm for the acoustic signals, numerous features in the time and frequency domains were extracted, with which multiple machine learning algorithms were trained and compared concerning their performance. A light gradient boosting machine was identified as a suitable machine learning model for weld seam classification. Finally, hyperparameter tuning was conducted, which resulted in a cross-validation accuracy of 94.78%, depending on the quality categories considered.

Laser-Induced Graphene for Advanced Sensing: Comprehensive Review of Applications.

Laser-induced graphene (LIG) and Laser-scribed graphene (LSG) are both advanced materials with significant potential in various applications, particularly in the field of sustainable sensors. The practical uses of LIG (LSG), which include gas detection, biological process monitoring, strain assessment, and environmental variable tracking, are thoroughly examined in this review paper. Its tunable characteristics distinguish LIG (LSG), which is developed from accurate laser beam modulation on polymeric substrates, and they are essential in advancing sensing technologies in many applications. The recent advances in LIG (LSG) applications include energy storage, biosensing, and electronics by steadily advancing efficiency and versatility. The remarkable flexibility of LIG (LSG) and its transformative potential in regard to sensor manufacturing and utilization are highlighted in this manuscript. Moreover, it thoroughly examines the various fabrication methods used in LIG (LSG) production, highlighting precision and adaptability. This review navigates the difficulties that are encountered in regard to implementing LIG sensors and looks ahead to future developments that will propel the industry forward. This paper provides a comprehensive summary of the latest research in LIG (LSG) and elucidates this innovative material's advanced and sustainable elements.

Synthesis and study of nonlinear optical properties of an enaminone derived from dibenzoylmethane and N,N-diethylaminoaniline

The compound, (Z)-3-((4-(diethylamino)phenyl)amino)-1,3-diphenylprop-2-en-1-one, is synthesized by the reaction of dibenzoylmethane and 4-N,N-diethylaniline. The relative stabilities of the possible tautomers of the molecule are studied via the DFT B3LYP-D3BJ, CAM-B3LYP, M062X, and ωB97XD functionals in conjunction with the 6-311++G(d,p) basis set. The results showed that the enaminone tautomer with the intramolecularly hydrogen bonded chelated ring is the most stable. This is further confirmed by the Car–Parrinello MD calculations in the gas phase as well as the NCI analysis. The electronic spectrum is calculated by the TD DFT B3LYP/c-pVDZ level in ethanol, and the hole–electron analysis is carried out for the interpretation of the bands, which revealed that the longest one at 430 nm is of charge transfer origin while the others are of local transition origin. Atoms-in-molecules calculations in several media and levels of theory predicted that the ρBCP at the hydrogen bond in the gas phase to be 0.03791–0.04255 e/a0 3 which is a characteristic of a medium strong hydrogen bond. Researchers investigated the enaminone’s nonlinear optical (NLO) characteristics when it was exposed to a low power (<1 Watt), single fundamental transverse mode laser beam at 473 nm. By using diffraction patterns (DPs) and Z-scan methods, we calculated the nonlinear refractive index (NLRI) of the enaminone up to 4.597 × 10−11 m2 W−1 using DPs. The resulting DPs are numerically investigated using the Fraunhofer (F.) approximation and the Fresnel-Kirchhoff (F.K.) diffraction integral, showing excellent agreement with experimental findings. We successfully explored all-optical switching (AOS) in enaminone using two laser beams.

Impact of altering phase modulation and geometrical shape of laser beam via a phase-only spatial light modulator on laser-induced fluorescence

This study investigates the impact of modulating and shaping a laser beam via a phase-only spatial light modulator (SLM) on the intensity of the laser-induced fluorescence (LIF) signal. Different phase modulations ranging from 0 to 2π are applied to the SLM window to evaluate the effect of the modulated beam on the emitted LIF signal from extra virgin olive oil EVOO samples. The laser beam is also shaped into circular and square geometries with varying diameters to determine the optimum size for maximizing the LIF signal strength. The results reveal that the highest LIF signal intensity could be obtained after modulating the incident laser beam with phase shifts of 0 and 2π, with an improvement factor of approximately 3 for Avanti olive oil and 1.42 for Al Jouf olive oil. Furthermore, laser beam shaping into a circular aperture with a radius of 2.45 mm or a square aperture with a side length of 2.45 mm yields the highest LIF signal improvement, with enhancement factors of approximately 2.9 for Avanti olive oil and 1.42 for Al Jouf olive oil. This work demonstrates the potential of SLM-based beam shaping techniques to optimize LIF measurements by tailoring the wavefront characteristics of the excitation laser source.

Research on the intensity profiles of high-order Laguerre-Gaussian mode laser beams

Here we analyzed the intensity profile properties of the Laguerre-Gaussian (LG) mode laser beams, to facilitate the intracavity intensity modulation for high-order LG mode laser output. The commonly used definitions of ring-like beam size are discussed, including the second moment of light intensity, power in the bucket, and the peak intensity radius of the ring-like beam. The differences between these methods underscore the importance of selecting appropriate beam size definitions when estimating the mode order, which is particularly worthy of attention when employing certain mode-selection techniques, such as using a defect spot, an aperture, or inducing spherical aberration (SA), to achieve high-order mode outputs. In the experiment, high-order mode LG0,±m output were obtained by utilizing the SA of a short-focal lens in the cavity of an end-pumped Nd:YVO4 laser at 1064 nm. The highest angular indices m reached 355, which is the highest order of LG mode output obtained directly from a laser cavity. The experimental relationship between the mode-order and cavity parameters matched well with the theoretical results, validating the analysis of the intensity profile properties.

Effects of Beam Mode on Hole Properties in Laser Processing

The laser beam mode affects the power density distribution on the irradiated target, directly influencing the product quality in laser processing, especially the hole quality in laser drilling. The Gaussian beam shape, Mexican-Hat beam shape, Double-Hump beam shape, and Top-Hat beam shape are four typical laser beam modes used as a laser heat source and introduced into our proficient laser-drilling model, which involves complex physical phenomena such as heat and mass transfer, solid/liquid/gas phase changes, and two-phase flow. Simulations were conducted on an aluminum target, and the accuracy was verified using experimental data. The results of the simulations for the fundamental understanding of this laser–material interaction are presented in this paper; in particular, the hole shape, including the depth–diameter ratio and the angle of the cone, as well as spatter phenomena and, thus, the formed recast layer, are compared and analyzed in detail in this paper. This study can provide a reference for the optimization of the laser-drilling process, especially the selection of laser beam mode.

Porosity suppression and mechanical property improvement of wire-arc directed energy deposited TiCp/Al-Cu alloys joint by oscillating pulsed wave laser beam welding

Hybrid manufacturing technology combining wire-arc directed energy deposition (WA-DED) and laser beam welding (LBW) presents a promising avenue for efficiently manufacturing large-size aluminum alloy components. The high tendency of porosity defects, particle decomposition, and fusion zone softening are outstanding challenges in the LBW welding of additively manufactured particle-reinforced aluminum alloys. Herein, a WA-DED-processed Al-6.3Cu alloy embedded with 0.6 wt% TiC particles was employed as weldment. Four different laser beam modes, including continuous wave (CW), pulsed wave (PW), oscillating continuous wave (OCW), and oscillating pulsed wave (OPW), were used to join TiCp/Al-6.3Cu alloy. The effects of different laser modes on the porosity defects, microstructure evolution, and mechanical properties of WA-DED particle-containing aluminum alloy joints were studied comparatively. Multi-scale characterization results showed that the enhanced molten pool flow via laser beam modulation effectively suppressed porosity defects and facilitated the uniform particle distribution. The OPW mode provides an optimal effect on porosity inhibition and weld microstructure refinement compared to the pulsed or oscillating modulation modes. The heat-treated LBW joint via OPW mode achieved excellent comprehensive mechanical properties, whose elongation and ultimate tensile strength reached 9.5% and 449 MPa, respectively. This enhanced performance can be attributed to the decreased porosity, refined weld microstructure, and high-density nano-precipitation. This study provides fundamental guidance for the welding of high-strength Al-Cu alloy fabricated by additive manufacturing.

Curcumin analogue: Synthesis, DFT and nonlinear optical studies

The synthesis of a new curcumin analogue dye via 3-chloro-2,4-pentanedion condensing with an aromatic aldehyde is considered. Following that, the synthesized compound is diagnosed utilizing spectroscopic methods, including FTIR, mass, 1H NMR, and 13CNMR. The curcumin analogue geometric optimization and theoretical studies are conducted on thermodynamic properties using DFT. The B3LYP techniques, which are hybrid functional with a 6–311+G(d) as the basis set, are adopted to compute the HOMO, LUMO, and Mullikan atom charges of the studied compound. The curcumin analogue dye nonlinear optical (NLO) properties are examined under excitation with a 473 nm, low power, cw and TEM00 mode laser beam. The index of nonlinear refraction (INLR) and coefficient of nonlinear absorption (CNLA) are estimated using diffraction patterns for the former and Z-scan for the latter. The INLR reaches a value as high as 6.86×10−11 m2/W, while the CNLA reaches 2.23×10−3 cm/W. All-optical switching (AOS) is tested in the novel curcumin analogue dye using two methods: static AOS and dynamic AOS.

High-reliability infrared broadband thin-film polarizing beam splitter with ZnSe compensation layers.

Thin-film polarizing beam splitters (PBSs) fulfill a pivotal role in laser beam splitting, modulation, shaping and isolation. In this study, a high-reliability infrared broadband thin-film PBS was developed. To correct for tensile stress in Ge/YbF3 multilayer coatings, ZnSe compensation layers were incorporated in the multilayer design. The effects of different symmetrical periods on the spectral properties of the infrared PBS were systematically discussed. The infrared PBS operated at 45° and in the long-wave infrared (LWIR) band. Using the percent of optical extrema monitoring (POEM) strategy combined with the high-temperature optical constants (HTOC) of Ge film, the infrared PBS was precisely fabricated on ZnSe substrates. Subsequently, the spectral performance and film reliability of the infrared PBS were carefully characterized. Specifically, the transmittance of p-polarization surpassed 96%, while the extinction ratio exceeded 100:1 within the 10.6 ± 0.15 µm band. The infrared PBS demonstrated commendable environmental reliability, in addition to exhibiting excellent spectral characteristics.

Describing the effect of local gas flow on keyhole and melt flow dynamics utilizing high-speed synchrotron X-ray imaging and numerical simulation

Laser beam welding with partial gas shielding using local gas flows has been shown to be very effective in reducing spatter, especially when welding high-alloy steels at high processing speeds (≥ 8 m/min). This paper examines the gas flow induced mechanical effect on keyhole geometry and correlating melt flow by means of a computational fluid dynamics analysis. Therefore, keyhole mode laser beam welding of AISI304 was modeled by using the volume of fluid method in FLOW-3D. The mechanical effect of the partial shielding was implemented by considering the gas flow induced dynamic pressure. By varying flow rates, a widening, and a reduction in fluctuation amplitude of the keyhole rear wall was detected. Furthermore, the melt flow dynamics were characterized by less flow velocity and melt movement. The results were validated by a visual comparison with high-speed synchrotron X-ray imaging, showing a high degree of agreement in modeling accuracy of the keyhole dynamics.

Fast spatial laser beam modulation for improved process control in Laser Powder Bed Fusion

We report on the implementation of a high frequency beam oscillation (wobbling) strategy for improving process control during laser powder bed fusion of single weld tracks on Inconel 625. Oscillation frequencies ranging from ~ 600 Hz to 7000 Hz, and different oscillation trajectories (circular, parallel or perpendicular to the direction of scanning) were explored. Highspeed imaging was used to elucidate the dynamics of the melt pool induced by the wobble beams, along with in situ absorptivity measurements to substantiate our hypothesis that the dynamic nature of wobble beams reduces absorptive losses due to laser-vapor interactions and results in improved coupling at the melt pool. Operando X-ray radiography was carried out to visualize sub-surface melt flow dynamics, correlate to spatter mechanisms and optimize the window for improving process stability. Our observations indicate that wobble beams increase the aspect ratio of the melt pool by up to 4×, depending on the oscillation frequency and energy input. Highspeed imaging and X-ray radiography reveal an optimized process parameter window for reducing spatter, improving absorptivity and creating a stable melt pool at high (several kHz) oscillation frequencies.

Review on Recent Laser Welding Trend in Electric Powered Vehicle Production

In this study, we summarize the state-of-the-art laser welding used for welding copper and aluminum alloys, which are key materials for electrified powertrain components. Extensive research on laser beam modulation, power control, beam control, and process monitoring to improve welding reliability and to solve the challenges of dissimilar welds are reviewed and summarized. Furthermore, various techniques for real-time behavior of the weld pool and weld quality monitoring are presented. Along with various techniques to improve spatter and weld pool instability during welding, we have also included research results on process monitoring using artificial intelligence and deep learning techniques. Moreover, computer simulation helps understand various welding phenomena. The research results on improving the quality of welded products through laser beam dynamic control are also included.

Effect of partial and global shielding on surface-driven phenomena in keyhole mode laser beam welding

Partial shielding by means of local gas supply has proven to be very effective in reducing spatter. Besides the effect of gas-induced dynamic pressure, the shielding of oxygen is also highly relevant for melt pool dynamics and spatter formation due to the growth of oxides and the influence on surface tension. Therefore, this paper addresses the effect of local supplied argon on oxide growth and seam topography during keyhole mode laser beam welding of high-alloy steel AISI 304. To determine the shielding quality, the results are compared to laser beam welding in a global argon atmosphere. The topography of the upper weld seams was analyzed by scanning electron microscopy (SEM). An X-ray microanalysis (EDX) in line scan modus was performed to determine and to locate the elements which are covering the specimen surface. The chemical state of the found elements was quantified by X-ray photoelectron spectroscopy (XPS). In a last step, high-speed synchrotron X-ray imaging was performed to separate the effect of the gas-induced pressure and the gas-induced shielding on keyhole geometry. The results show that a local supply of argon contributes to a significant difference in oxide growth, affecting melt pool convection and weld seam geometry. It was further shown that the effect of gas flows at low flow rates is primarily because of oxygen shielding, as no significant difference in keyhole geometry was found by high-speed synchrotron X-ray imaging.

Reflection and refraction of higher-order Hermite-Gaussian beams: a vector wave analysis.

Hermite-Gaussian beams, as a typical kind of higher-order mode laser beams, have attracted intensive attention because of their interesting properties and potential applications. In this paper, a full vector wave analysis of the higher-order Hermite-Gaussian beams upon reflection and refraction is reported. The explicit analytical expressions for the electric and magnetic field components of the reflected and refracted Hermite-Gaussian beams are derived with the aid of angular spectrum representation and vector potential in the Lorenz gauge. Based on the derived analytical expressions, local field distributions of higher-order Hermite-Gaussian beams reflection and refraction at a plane interface between air and BK7 glass are displayed and analyzed.

Tailoring the weld microstructure to prevent solidification cracking in remote laser welding of AA6005 aluminium alloys using adjustable ringmode beam

Solidification cracking is a prevalent defect in welding aluminium alloys which can be effectively mitigated by employing grain refinement strategies. This paper investigates the feasibility of tailoring the weld zone grain structure of 6xxx series aluminium alloys using an adjustable ring mode (ARM) laser beam to reduce the centreline cracking susceptibility. An in-process monitoring approach, comprising a high-speed camera and an ad-hoc Digital Image Correlation, was adopted to examine the strain development during laser welding on a self-restraint test rig. Results revealed that transverse strain in the weld centre exhibits a parabola-like relationship with the core/ring power ratio, with the minimum strain determined at the power ratio of ∼1.5, regardless of the total power employed. The microstructural analysis demonstrated that increasing the core/ring power ratio can lead to the refinement of columnar and equiaxed grains. Furthermore, the formation of secondary equiaxed grains is promoted when the power ratio increases, and this is proved to be related to the characteristic of the ARM laser by the like-for-like comparison. Overall, a fine-tuned power ratio of 1.5 is determined in the studied material and welding configuration for achieving a centreline crack free weld, benefiting from the improved microstructure and reduced thermal strain.

Thermal and Nonlinear Optical Properties of Sudan III.

We report the experimental and theoretical study of the diffraction patterns (DPs) and thermal properties of Sudan III. DPs are used in the calculation of the Sudan III nonlinear refractive index (NLRI), . As high as = 7.69 ×10-6 cm2/W is obtained. The study of the Sudan III thermal conductivity, TC, shows the reduction of the TC against the increase of the Sudan III temperature. The property, all-optical switching (AOS), is studied in details, both static and dynamic ones, using two, cw, visible, single mode laser beams of wavelengths 473 and 635 nm.

Generation of terahertz radiation by a Hermite–Gaussian laser beam inside magnetoplasma with a density ramp

In the present scheme of work, the Hermite–Gaussian (HG) laser beam dynamics has been investigated under the influence of an upward density ramp inside magnetized plasma, where both relativistic and ponderomotive nonlinearities are operative. One can achieve self-focusing of laser beam due to the change in the medium's dielectric function, which comes into operation due to the expulsion of plasma electrons from the high intensity to the low-intensity region by ponderomotive force and their motion at relativistic speeds. The dynamics of the laser beam and terahertz generation have been investigated by using the moment theory approach. It has been observed from the present analysis that the dynamics of the laser beam and the production of terahertz radiations strongly depends upon the HG laser beam and plasma parameters. In addition to this, the effect of density ramp and magnetic field has also been investigated on the efficiency of terahertz generation. It has been observed that higher-order modes of the HG laser beam play a dominant role in the production of terahertz radiations.

Two laser beam modulation of microstructure and residual stress field in cold sprayed Al alloy for recovering fatigue performance

The cold spray (CS) process has been demonstrated to be an attractive additive manufacturing technology for the development of freeforms and coatings from temperature-sensitive materials. However, owing to the lower bonding strength and inhomogeneous residual stress field distribution, the fatigue performance of CS deposition cannot satisfy the requirements of numerous engineering conditions. This study proposes a novel and promising approach to recover the fatigue performance of CS-repaired Al alloy components using two laser beam modulations. In the treatment, a millisecond laser is used during the CS process to heat the impact location in situ, by which the bonding mode is transformed from mechanical bonding to metallurgical bonding, and massive Al2O3 reinforcements of nano/micro size are formed in the coating. Thus, the bonding strength is significantly improved. Next, another nanosecond laser is used as a post-treatment to act on the area except the repaired region of the sample, which optimised the residual stress distribution around the repaired zone by the mechanical effects of the laser-induced ultra-high shock waves. Through the combination of these two lasers, the fatigue performance of CS-repaired Al alloy samples is successfully restored to its original condition. This study demonstrates that this compound process of CS technology and laser processing presents a wide range of possibilities for further development of advanced repair technology.

All-fiber cascaded combiners for high-power adjustable-ring mode laser beam with a flattop central beam

An all-fiber structure that obtains an adjustable-ring mode (ARM) beam with a uniformly distributed central beam is put forward for the first time based on the beam combining technology. This structure is all-fiber cascaded combiners consisting of a 3 × 1 combiner and a (6 + 1) × 1 combiner in series. A multi-mode fiber with core diameter of 50 µm acts as the connective fiber, transmitting the combined laser of the first 3 × 1 combiner into the center guide core of the output fiber by the well-designed (6 + 1) × 1 combiner. Through the independent transmission of the center and ring beams, an 8.8 kW uniformly distributed central output laser with a transmission efficiency of 96.2 % and M2 of 5.24 is obtained by the cascaded combiners. The feasibility of ARM laser beam with a 10 kW-level flattop central beam provides a new approach for high-power laser welding.

A novel azo compound derived from ethyl-4-amino benzoate: synthesis, nonlinear optical properties and DFT investigations

A novel azo dye compound, Ethyl (E)-4-((5-hydroxy-3,4-bis(hydroxyl methyl)-6-methyl. pyridin-2-yl)diazenyl)benzoate (EAB), have been synthesized by the coupling reaction and characterized by FT-IR, 1H-and 13C-NMR, Mass, and UV–visible spectroscopies. The nonlinear optical (NLO) properties of the EAB compound via the finding of the nonlinear refractive index (NRI) using continuous wave (cw), low power 473 nm, TEM00 mode laser beam have been studied via the diffraction patterns (DPs) and the Z-scan. Effect of power input of the laser beam, types of beam wavefront and temporal variation of the DPs are discussed. The all-optical switching (AOS) using two laser beams is proved to occur in this compound.