Conventional Laser Research Articles

Evaluation of H-/D- Density Using Langmuir Probe Measurement in a Cs Seeded Negative Ion Source

An electron reduction model is reintroduced for Langmuir probe plasma density profile measurement. The model is compared with conventional laser photo-detachment measurements and can predict negative ion density in the 2-3 x 1017m−3 range using correlation factors for hydrogen and deuterium cases. The calibration and correction procedure is demonstrated for application to ion sources.

Turnkey locking of quantum-dot lasers directly grown on Si

Ultralow-noise laser sources are crucial for a variety of applications, including microwave synthesizers, optical gyroscopes and the manipulation of quantum systems. Silicon photonics has emerged as a promising solution for high-coherence applications due to its ability to reduce the system size, weight, power consumption and cost. Semiconductor lasers based on self-injection locking have achieved fibre laser coherence, but typically require a high-quality-factor external cavity to suppress coherence collapse through frequency-selective feedback. Lasers based on external-cavity locking are a low-cost and turnkey operation option, but their coherence is generally inferior to self-injection locking lasers. In this work, we demonstrate quantum-dot lasers grown directly on Si that achieve self-injection-locking laser coherence under turnkey external-cavity locking. The high-performance quantum-dot laser offers a scalable and low-cost heteroepitaxial integration platform. Moreover, the chaos-free nature of the quantum-dot laser enables a 16 Hz Lorentzian linewidth under external-cavity locking using a low-quality-factor external cavity, and improves the frequency noise by an additional order of magnitude compared with conventional quantum-well lasers.

Crackless high-aspect-ratio processing of a silica glass with a temporally shaped ultrafast laser.

In this Letter, we propose a crackless high-aspect-ratio processing method based on a temporally shaped ultrafast laser. The laser pulse is temporally split into two sub pulses: one with smaller energy is used to excite electrons but without ablation so that the applied pressure to the sample is weak, and the other one is used to heat the electrons and achieve material removal after it is temporally stretched by a chirped volume Bragg grating (CVBG). Compared with the conventional ultrafast laser processing, the crack generation is almost suppressed by using this proposed method. The hole depth increases more than 3.3 times, and the aspect ratio is improved at least 2.2 times. Moreover, processing dynamics and parameter dependence are further experimentally studied. It shows that the processing highly depends on the density of electrons excited by the first pulse (P1) and the energy of the second pulse (P2). This novel, to the best of our knowledge, method provides a new route for the precise processing of wide-bandgap materials.

Microstructural and electrochemical behaviour of severely surface-deformed 316L steel manufactured by conventional and selective laser melting routes

This study thoroughly examines the influence of conventional and selective laser melting (SLM) routes and surface mechanical attrition treatment (SMAT) on the microstructural and electrochemical properties of 316L steel. Compared to wrought specimens, the SLM specimens exhibit significantly smaller grains (∼41 vs. ∼83 µm) and higher dislocation density (∼7.2 × 1013 vs. ∼3.7 × 1012 m−2). Both specimens show nearly doubled surface hardness after SMAT, with the SLM surface displaying a ∼30 nm grain size and minimal α’ phase. The microstructure significantly influences passivation and corrosion behaviour. The SLM specimens exhibit superior electrochemical characteristics to wrought counterparts in SMATed (0.00299 mmpy) and non-SMATed (0.00771 mmpy) conditions. SMAT effectively eliminates surface porosity, enhancing the passivation and corrosion resistance of SLM steel.

Design optimization of Yb-doped fiber lasers for operation in radiation environments

AbstractRadiation hardening should be considered for various active fiber systems operated in adverse environments to reduce their sensitivity to complex ionizing radiations. And, architecture optimization through numerical simulation provides an efficient choice. Here, introducing radiation effects into the conventional fiber laser model, a radiation model concerning the design optimization of low- and moderate-power Yb-doped fiber lasers is developed. And, experiments at different radiation levels up to 750 Gy are carried out for validation, demonstrating the ability of this model to correctly simulate the performance of the Yb-doped fiber laser in harsh environments. Then, with this model, impacts of active fiber length, pump scheme, and pump allocation on the output characteristics of Yb-doped fiber lasers are analyzed numerically. And, optimization of Yb-doped fiber lasers are conducted through architecture design. Simulations show that a proper design with relatively short active fiber and dynamic pump allocation can remarkably improve the radiation tolerance of Yb-doped fiber lasers.

Six-month results of 577 nm subthreshold micropulse laser therapy in non-center involving diabetic macular edema

BackgroundThis study aimed to evaluate the efficacy of 577 nm subthreshold micropulse laser (SML) therapy in patients with non-center involving diabetic macular edema (DME). MethodsTwenty-two eyes of 18 patients diagnosed with non-center involving DME were included in this prospective, observational study. The patient's baseline best corrected visual acuity (BCVA), maximum retinal thickness (MRT), central macular thickness (CMT), and the area of macular exudates were determined and re-evaluated at 1, 3, and 6 months after laser treatment. ResultsThere was no statistically significant change in BCVA at the 1st, 3rd and 6th months compared to the baseline in the follow-up (p = 0.067, p = 0.270, p = 0.027 according to Bonferroni correction p < 0,01). 1st, 3rd, and 6th month MRT was statistically significantly lower than baseline (p = 0,009, p = 0,006, p = 0,007). No statistically significant change was detected in CMT at the 1st, 3rd and 6th months compared to the baseline in the follow-up (p = 0.384, p = 0.794, p = 0.363). No statistically significant change in the area of macular exudates was detected at the 1st, 3rd, and 6th months compared to the baseline (p = 0.904, p = 0.444, p = 0.277). ConclusionsThis study observed a significant decrease in extrafoveal retinal thickness in patients with DME. There was no progression to central macular involvement, an increase in the area of exudates, and a decrease in BCVA in any patient. SML may be an effective alternative to conventional argon laser in non-center involving DME.

The Pre-Heating Effect for Porosity Control during the Laser Welding of Galvanized Steel Sheets

Recently, for the high performance of automobiles, the application ratio of zinc-coated steel sheets with excellent corrosion resistance has been increasing. However, it is difficult to achieve sound welds, as porosities form from zinc during welding. In this study, a laser welding process, with the addition of a pretreatment step to conventional laser welding, was devised to improve weld quality by eliminating pores caused by zinc in the welds. Laser welding was performed on the overlapping joint of hot-dip galvanized steel sheets (SGARC 340, Hyundai Steel., Suncheon-Si, Jeollanam-do, Republic of Korea), with a thickness of 1.2 mm in the upper sheet and 0.9 mm in the lower sheet, and the welding characteristics were investigated by varying the laser power and focal position. Compared to conventional laser welding, the three-step laser stitch welding process significantly reduced the degree of spatter generation and welding defects. Additionally, it increased the tensile–shear load by approximately 37%. Moreover, the reduction in the zinc component of the three-step laser stitch welds was confirmed through SEM-EDS analysis. These findings contribute valuable information for securing high-quality welding joints and effectively addressing zinc-coated steel sheet welding quality issues in the automotive and industrial sectors.

Deep Learning Neural Network (DNN) Coupled Laser Induced Breakdown Spectroscopy for Quantitative Analysis of Copper Alloys

Conventional Laser Induced Breakdown Spectroscopy (LIBS) quantitative analysis, employing both calibration and calibration-free techniques, is challenged by spectral overlapping, self-absorption, and spectral broadening effects, leading to decreased accuracy. Recently, integration of machine learning (ML) algorithms with LIBS has been increasingly employed to tackle these challenges. This article explores the augmentation of LIBS with deep learning neural networks (DNN) to enhance accuracy of quantitative analysis of multi-elemental copper alloys. Sufficient training data was acquired by simulating optical emission spectra for bronze (Cu-Sn) and admiralty brass (Cu-Zn-Sn) alloys under standard laser produced plasmas conditions, encompassing different alloy concentrations, electron temperatures, and densities. We designed a regularized DNN structure, fine-tuned using a validation dataset to optimize quantitative results. The model’s accuracy was assessed with test dataset. The quantitative results demonstrated reduced loss as training spectra increased from 500 to 5000 for both alloys. The decline in mean squared error, from 2.793×10−3 to 4.283×10−5 for bronze and from 3.245×10−2 to 5.598×10−4 for admiralty brass alloys, as training data increased from 500 to 5000, underscores the proposed DNN model’s potential for metallurgical alloy quantification.

An improved laser flash method for thermal conductivity measurement of molten salts

Thermal conductivity measurement of high-temperature heat transfer fluids provides a crucial basis for designing utility-scale thermal systems. Molten salts are promising heat transfer and thermal storage fluids in high-temperature thermal energy storage systems, while the molten salt thermal conductivity obtained in existing studies exhibits large deviations due to the high experimental complexity and unstandardized test procedures. In this work, we improve the conventional laser flash analysis method by proposing a theoretical heat transfer model for multi-layer heat conduction and providing a near-optimal molten salt container design. With water as a test sample, the relative error of thermal conductivity measurement using the improved method is 6.3%. The thermal conductivity of Solar Salt from 250 to 400 ​°C, and of Hitec Salt from 160 to 250 ​°C are measured and compared with the previous work. Both results show that the thermal conductivity increases with the temperature rising. This work will promote the technology standardization for accurately acquiring the thermal conductivity of molten salts or other similar high-temperature heat transfer fluids.

Management of Abnormal Frenulum and Gingival Enlargement in One Visit

Gingival enlargement or excessive gingival growth, is a common occurrence in gingival disease, characterized by an increase in the size of the gingiva. Inflammatory gingival enlargement or inflammatory gingival enlargement is an inflammatory response to local irritation related to the gingiva. The most frequently performed treatment for gingival enlargement is gingivectomy. A high frenulum makes it easier for the gingival margin to be pulled so that plaque is easily trapped in the sulcus which results in periodontal disease and can be corrected with a frenectomy procedure. A 22-year-old female patient came to RSGM UMY complaining that her upper front gums had become enlarged so she was lacking self-confidence. Intraoral objective examination revealed enlarged gingiva on the interdental papillae of the maxillary anterior teeth (12, 13, and 21) which were rounded, light red in color with the surrounding gingiva, and had a smooth surface. There is a high frenulum with a height of 8 mm. A blanching test was carried out to examine the frenulum and the results were positive (+).Gingivectomy can be performed with a conventional scalpel, electrosurgery, chemosurgery, and laser. Conventional gingivectomy surgery performed with a small scalpel has been considered the most common method due to its ease of use, accuracy, and minimal tissue damage. Frenectomy can also be performed using various methods, such as using a scalpel, electrosurgery, or laser. Gingivectomy and frenectomy surgical procedures are effective in managing enlarged gingiva with a high frenulum

Study on improvement of weld defect in oscillating laser welding of aluminum alloy T-joints assisted by solder patch

During oscillating laser welding of aluminum alloy T-joints assisted by solder patch, it is found that the pore defect can be reduced and the high quality welded T-joints are obtained. To understand the effect of oscillating laser on the formation process of T-joint welds, a dynamic model for laser welding of aluminum alloy T-joints assisted by solder patch is developed in this paper to analyze the dynamic behaviors of keyhole and molten pool. Based on the dynamic model, the morphology characteristics of keyhole and the evolution processes of molten pool temperature and flow fields during conventional laser welding and oscillating laser welding are calculated and compared. The simulation results are found to be kept consistent with the experimental results. It is demonstrated that the keyhole is characterized with better morphology and higher stability and the degassing condition of molten pool is improved during oscillating laser welding compared with conventional laser welding. The molten pool temperature and flow fields are much more uniform during oscillating laser welding. The obtained results are efficient for suppressing weld defects and achieving high quality welding of aluminum alloy T-joints.

Microgrooves with Small Taper Angle Processed by Nanosecond Laser in Closed Flowing Water.

To improve the capability of nanosecond lasers to process structures with a high aspect ratio, a new method of nanosecond laser processing in closed flowing water was proposed in this paper. The microgrooves on a stainless steel 304 surface were processed by the new method, and the influence of processing parameters on the microgrooves was studied. The comparative experiments of laser processing in still water and overflowing water were also carried out, and the unusual phenomenon of laser processing in different flowing water was discovered by a high-speed camera. The results showed that the flowing velocity played a crucial role in underwater laser processing, and that high flowing velocity could timely remove bubbles in closed flowing water, thus obtaining higher processing efficiency. As the depth of the groove increased, the bubbles firstly affected the processing of the sidewall, causing a circular transition between the sidewall and bottom surface. The reflection of the laser beam by the bubble could cause secondary processing on the sidewall, resulting in a decrease in the taper angle. Based on the above research, the microgroove with a width of 0.5 mm, aspect ratio of 3, and taper angle of 87.57° was successfully processed by a nanosecond laser in closed flowing water. Compared to conventional nanosecond laser processing, laser processing in closed flowing water was more advantageous in processing microgrooves with a small taper angle and high aspect ratio.

Simple modulation of Lissajous MEMS laser beam scanning with reconfigurable structured light patterns for 3D imaging

Structured light 3D imaging systems commonly employ panel-based projectors or 1-axis MEMS mirrors with beam expander lens to project multi-frame barcodes or dot clouds, addressing challenges posed by objects with multi-scale feature sizes. However, these methods often result in large system volumes due to the required projection multi-lens modules, high hardware costs, or limited light pattern generation capabilities that hindering measurement precision enhancement. This paper introduces an innovative approach to reconfigurable spatial light pattern projection using a single bi-axial MEMS mirror with Lissajous scanning. In contrast to the pixel-by-pixel pre-defined image patterns encoding of conventional 2D laser beam scanning, the proposed method simply aligns the MEMS bi-axial resonance frequencies with laser pulse modulation, enabling the projection of diverse structured light patterns such as stripes, lines, dot matrices, and random dot clouds, which can adapt to different 3D imaging algorithms demands. It eliminates the need for multi-frame encoding and streamlines data caching, simplifies digital logic hardware. A prototype 3D imaging system was developed to demonstrate the mathematical model for laser modulation and the technical feasibility based on the proposed principle. Beyond its lens-free essence, the system supports focal-free optics and a compact projection form factor, which accommodates to a broad range of projection distances and field-of-views based on object’s location. 3D depth map of polynomial surface and blocks objects are extracted through single-frame pattern projection with a relative high accuracy. The presented modulation theory for diverse structured light pattern generation opens avenues for versatile and compact 3D imaging applications of LiDAR and robotic 3D vision.

Surface roughness optimization of hybrid PBF-LB/M-built Inconel 718 using in situ high-speed milling

We report on the optimization of the surface roughness of hybrid additive manufactured Ni superalloys, combining a conventional laser powder bed fusion process with in situ high-speed milling. This remarkable hybrid approach has only recently been applied to different steel types and barely to Ni superalloys which opposite to steel appear to be challenging for milling processes, particularly within the powderbed of laser powder bed fusion. Different influencing factors on the surface roughness are varied in this study, following the Taguchi method. Their effect is evaluated with respect to the average surface roughness and the maximum surface roughness. The signal-to-noise ratio for the varied parameters infeed, z-pitch, feed rate, and spindle speed is calculated, determining their relevance on the surface roughness, and defining an optimal parameter combination. As the surface quality is optimized to Ra=0.47μm\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\varvec{R_a=0.47\\, \\mu m}$$\\end{document}, the definition of the optimal parameter combination is of the highest relevance for the application of this novel manufacturing approach for Inconel. Using linear regression, the resulting surface roughness of these parameters is predicted, getting validated by the experimental evaluation. Due to a further analysis, including EDX analysis and a quantitative element analysis at different positions of the flank of the milling cutter, wear characteristics as well as the dissipation of the coating of the milling cutter are detected. The flank wear and the resulting breakage of the cutting edge are defined as the main reasons of a rising surface roughness.

Ultrafast laser bursts welding glass and metal with solder paste to create an ultra-large molten pool.

A novel, to our knowledge, method is proposed for the welding of glass and metal with a large gap filled with solder paste using ultrafast laser bursts. The addition of solder paste enables a reliable glass-metal connection even at gaps of hundreds of microns, while the position of the glass can be flexibly adjusted. By ultrafast laser bursts, the volume of the molten pool increases significantly, and the height of the molten pool reaches approximately 350 µm, which is more than an order of magnitude higher than that of conventional ultrafast lasers (10-20 µm). Cross-sectional analysis of the welded region shows that extensive material mixing and element diffusion occur, and stable connections are achieved at multiple interfaces. An analysis of the interaction between the ultrafast laser bursts and the material, as well as the mixing of multiple materials during the welding process, leads to a clear welding mechanism.

Effect of laser shock peening without coating on fretting wear behavior of GH4169 superalloy at high-temperature

Improving the high-temperature wear resistance of aero-engine components is critical. Laser shock peening without coating (LSPwC) seems to have more potential because of lower morphology changes and simpler processing compared with conventional laser shock peening (LSP) techniques. The influence of LSPwC process and test temperature on the fretting wear behavior of GH4169 superalloy for 2 × 105 cycles was investigated. The results indicate that a molten layer and a hardened layer are formed sequentially below the periodic dimple structure under the combination of shock wave and thermal effect. The formation of hardened layer enhances the difficulty of abrasive ploughing and the increase in test temperature promotes the generation of a glaze layer. Therefore, both LSPwC process and high temperature cause a reduction in wear volume. However, the main wear mechanism is similar before and after LSPwC. Besides, the protective mechanism of glaze layer under the gross slip regime may be ascribed to the frictional sintering process.

Fabrication of crack-free aluminum alloy 6061 parts using laser foil printing process

PurposeThis paper aims to present the fabrication of 6061 aluminum alloy (AA6061) using a promising laser additive manufacturing process, called the laser-foil-printing (LFP) process. The process window of AA6061 in LFP was established to optimize process parameters for the fabrication of high strength, dense and crack-free parts even though AA6061 is challenging for laser additive manufacturing processes due to hot-cracking issues.Design/methodology/approachThe multilayers AA6061 parts were fabricated by LFP to characterize for cracks and porosity. Mechanical properties of the LFP-fabricated AA6061 parts were tested using Vicker’s microhardness and tensile testes. The electron backscattered diffraction (EBSD) technique was used to reveal the grain structure and preferred orientation of AA6061 parts.FindingsThe crack-free AA6061 parts with a high relative density of 99.8% were successfully fabricated using the optimal process parameters in LFP. The LFP-fabricated parts exhibited exceptional tensile strength and comparable ductility compared to AA6061 samples fabricated by conventional laser powder bed fusion (LPBF) processes. The EBSD result shows the formation of cracks was correlated with the cooling rate of the melt pool as cracks tended to develop within finer grain structures, which were formed in a shorter solidification time and higher cooling rate.Originality/valueThis study presents the pioneering achievement of fabricating crack-free AA6061 parts using LFP without the necessity of preheating the substrate or mixing nanoparticles into the melt pool during the laser melting. The study includes a comprehensive examination of both the mechanical properties and grain structures, with comparisons made to parts produced through the traditional LPBF method.

Subthreshold laser treatment for non-center involved diabetic macular edema via non-damaging retinal laser therapy (NRT).

To evaluate the efficacy of subthreshold laser treatment via non-damaging retinal laser therapy (NRT) in patients with non-center involved diabetic macular edema (non-CI DME). In this prospective controlled study, NRT with 577nm wavelength was performed to the edematous inner subfields as needed at 3 monthly intervals, while the control group received no treatment. If CI-DME developed in either group, intravitreal anti-VEGF was performed and the eye was excluded from subsequent analysis. A total of 75 eyes (36 study eyes, 39 controls) were evaluated. The change in superior, nasal and temporal inner subfield thicknesses over time and between groups was found significant (P = 0.004, P < 0.001, P = 0.04 respectively). Best corrected visual acuity (BCVA) change was not significant over time and between groups (P = 0.69). Rates of CI-DME development requiring intravitreal anti-VEGF treatment were not different during the first and second years (P = 0.171, 0.908). No laser scar was detected in any eye in fundus autofluorescence imaging. NRT performed as needed at 3 monthly intervals is effective after 21months of follow up in the treatment of non-CI DME and it was safe. With this method, it may be foreseen that BCVA will be better preserved in the long term by avoiding the possible side effects of conventional laser.

Enhanced reduction of graphene oxide via laser-dispersion coupling: Towards large-scale, low-defect graphene for crease-free heat-dissipating membranes in advanced flexible electronics

The advancement of flexible electronics demands improved components, necessitating heat dissipation membranes (HDMs) to exhibit high thermal conductivity while maintaining structural integrity and performance stability even after extensive deformation. Herein, we have devised a laser-modulated reduction technique for graphene oxide (GO), enabling the fabrication of high-quality, large-scale, low-defect graphene, which yields high-performance HDMs after orderly deposition. The work underscores the crucial role of the laser wavelength and dispersion liquid’s coupling intensity in influencing the morphology and properties of graphene. Optimal coupling effect and energy conversion are realized when a laser of 1064 nm wavelength irradiates a triethylene glycol (TEG)/N,N-Dimethylformamide (DMF) dispersion. This unique synergy generates high transient energy, which facilitates the deprotonation process and ensures a swift, comprehensive GO reduction. In contrast to conventional water-based laser reduction methods, the accelerated reaction magnifies the size of the graphene sheets by mitigating the ablation effect. After membrane construction with an ordered structure, the corresponding membrane exhibits a high thermal conductivity of 1632 W m−1 K−1, requiring only ∼1/10 of the total preparation time required by other reported methods. Remarkably, the resulting HDM demonstrates superior resilience against creasing and folding, maintaining excellent smoothness and negligible reduction in thermal conductivity after violent rubbing. The combination of exceptional flexibility and thermal conductivity in HDMs paves the way for long-term practical use in the flexible electronics industry.

Femtosecond laser shock peening Cu-Zn welds: Experiments and multi-scale modeling investigation

Laser shock peening of the weld surface is a cutting-edge treatment technology following welding. However, the conventional nanosecond pulsed lasers used for this process can unintentionally damage the weld surface quality due to secondary melting, which can reduce the comprehensive mechanical properties of the material. Here, we applied femtosecond laser shock peening (FLSP) to Cu-Zn welds as a paradigm. Experimental results show that FLSP cause the finer grain size on the surface of welds, with the maximum increases of approximately 17.6 % in surface hardness of the welds. The residual stress on the surface was transformed from tensile residual stress to compressive residual stress. Crucially, to provide a more precise depiction of the FLSP process, we developed a comprehensive multi-scale modeling approach that involves integrating the inputs and outputs among models with different scales. This multi-scale modeling approach provides an enhanced understanding of the FLSP process compared to traditional single scale models. The high-density electron pressure evolution process, the shock compression fragmentation process of the weld dislocation network during FLSP and the depth of compressive residual stress could be investigated by this model. These findings provide electronic-level and atomic-level insights and imply promising applications of FLSP on various welds surface.