Multi-spot Laser Research Articles

Melt flow complexity in multi-spot laser welding of asymmetric T-joints

This study investigates melt flow dynamics in asymmetric T-joint laser welding, particularly with sheets inclined up to 45°. This complex scenario requires filler wire, accessible only from the flat sheet side. High-speed imaging at the top and root captures transient phenomena leading to weld imperfections. Research on stainless-steel involved the impact of first-order welding parameters on the weld quality. This included multi-spot laser welding with two beams. The analysis focused on melt pool dynamics under these challenging conditions. The asymmetric root side’s geometry necessitates proper melt flow to form a favorable root topology, avoiding defects like wavy roots and porosity. Key observations included intermittent keyhole openings, transient melt flow effects, and potential spatter ejection at the bottom. The findings offer a comprehensive understanding of 3D asymmetric melt flow, laying the analytical groundwork for enhancing the weld quality.

Research on Quadrant Detector Multi-Spot Position Detection Based on Orthogonal Frequency Division Multiplexing

Free space optical communication is developing towards laser communication networking. A novel method of quadrant detector (QD) multi-spot position detection based on orthogonal frequency division multiplexing (OFDM) is proposed for multi-spot laser communication systems. The mathematical model is constructed, and the Monte Carlo method is used to validate it. The position calculation of three beams incident on QD is simulated. The influence of key parameters on the accuracy of position detection is analyzed when the spots are at the same position and a different position. The results show that when the SNR of the system is 31.74 dB, the radius of the Gauss spot is 2 mm, the number of FFT (fast Fourier transform) points is 1024, and the center of the multi-spot is at the same position of the detector target; the accuracy of signal position detection calculated by the equation is 1.433 μm, and the simulation results are 1.351 μm, 1.354 μm, and 1.389 μm, respectively. When the center position of the multi-spot is at different positions of the detector target, the detection accuracy calculated by the formula is 1.438 μm, 1.433 μm, and 1.434 μm, respectively, and the simulation results are 1.419 μm, 1.387 μm, and 1.346 μm, respectively. The experimental results verify the effectiveness of the proposed multi-target simultaneous detection method. This article proposes a new multi-spot position detection method which can not only achieve one-to-multiple node laser communication but also improve the accuracy of point position detection.

A Study on Heat Flow Affects by Serial or Parallel Arrayed Multi-spot Laser Beam

A Study on Heat Flow Affects by Serial or Parallel Arrayed Multi-spot Laser Beam

Tube Sheet Annular Seam Measurement Technology Based on Laser Collaboration With Vision Sensor

The fast and accurate locating of the tube-sheet annular seam is the key factors to ensure the high efficiency and quality of automatic welding of pressure vessels. Considering the problems of welding sheet deformation and tubes deviation caused by machining process and welding thermal, this paper builds an automatic welding robot platform, which is equipped with a measurement system coordinated by multiple lasers and visual sensors, and put forward a real-time welding distance measurement method based on cross lasers and visual sensors, at the same time, the multi spot laser assisted vision sensor is used to quickly and accurately measure the center of the tube, so as to guide the adjustment of the welding robot and posture of the welding torch in real time. Then, through the measurements of system error, static and dynamic measurement error, it is known that the dynamic accuracy of tube sheet welding distance is not less than 0.22mm, and the positioning accuracy of welded tube center is not less than 0.219mm, which can meet the accuracy requirements of automatic tube sheet welding.

Multispot laser welding for increased gap bridgability

Laser beam welding is a promising technology to enable automated high-quality welding procedures at significantly higher processing speeds compared to conventional processes. However, its usability is often limited by gap bridgability. This disadvantage is related to the small laser beam spot sizes that require low gap sizes for joining, which are often practically not available, and the desired welding without additional filler materials to enable high processing speeds without direction restrictions. New possibilities of beam shaping for process control are also available now for high-power laser processing and they show promising results. The resulting complex effects require additional investigation to understand the mechanisms and the use of the technologies for process improvements. Therefore, in this work, advanced beam shaping optics with up to four separate laser beam spots was used to understand the impact of multiple-spot welding on the process dynamics and gap bridgability. Gap bridgability was measured by an opening gap setup, while spatter amounts as indicators of process dynamics were measured by high-speed imaging. It was shown that multiple-spot laser welding can increase the gap bridgability, probably due to the initiated melt flow toward the joining partners. Symmetric separation of the keyholes toward the sheets increased the gap bridgability, while additional low-intensity spots in the center were able to stabilize the melt pool and reduce spattering.

A novel design concept of cost-effective permanent rail-track monitoring system

This paper presents a novel design concept of low-cost permanent monitoring system for rail-track problems. The introduced design is theoretically overcome the currant in-use designs in terms of providing permanent accurate observations for detecting rail-track irregularities for all railway network during service time using low-cost integrated sensors. The paper investigates the rail-track common irregularities by identifying the issues, presenting challenges, and highlighting the limitations of currently in-use rail-track monitoring techniques. Then, the potential of using cost-effective sensors and intelligent techniques for detecting the rail-track geometric parameters and rail irregularities is theoretically studied. This includes using low-cost GPS, MEMS-INS & high frequency single-point and multi-spot laser distance sensors for detecting rail surface cracks, fractures, cross-level, wrap, gauge and vertical & horizontal rail alignments. Different levels of GPS/MEMS-INS integration are covered, illustrating the advantages of each solution and the optimal utilization in the system. Vision-based monitoring using low-cost HD non-metric digital cameras is also investigated, showing the optimal specifications required for fulfill the system requirements. Data logging and GPS-time-based synchronization method is presented as a part of the design concept of the suggested system. The processing techniques and unit outputs are illustrated in details, showing how each unit works for detecting the rail-track irregularities, providing the geodetic positioning and the vision-based assessing. The main part of the system, which is Automatic Adjusted Wheeled Carrier Frame (AAWCF) is discussed in more details, showing simple and clear different views for all details and integrated sensors. It is recommended to carry out this idea, by building up and evaluating the performance of AAWCF in real railway environments, evaluating the design concept of each unit individually to know the weaknesses of each technique, and then evaluating the whole system in all expected railway cases to find out the advantages and limitations of this design concept.

Holographic multi-spot generation for ultra-short pulse Bessel beam processing of stainless steel

Spatial Light Modulators are widely used for creating multiple laser spots with a flexible spatial distribution. This work presents an optical setup for multi-spot laser micro-drilling on stainless steel. For decreasing the hole diameter and getting high laser spot intensities, Bessel beams were generated. A phase only SLM was used as a beam splitter and a physical axicon was added to the setup. This separation of beam splitting and shaping is due to the higher diffraction efficiency of the axicon compared to holographic generated Bessel beams, especially for high cone angles. Minimizing the intensity losses is important due to the low damage threshold of SLM displays. Furthermore, additional lenses has been added for increasing the spot intensity. An ultra-short pulse Ti:Sa-laser (800 nm, 100 fs) was used for the experiments. Possible Bessel spot distributions for metal processing and the impact of the mutual influence of the spots were investigated.

Multispot optics for beam shaping of high-power single-mode and multimode lasers

The performance of various laser technologies, such as welding, laser powder bed fusion (LPBF), brazing, cladding, and sheet metal cutting, based on the use of high-power multimode fiber lasers, fiber-coupled solid-state, and diode lasers, can be improved using the patent pending beam-shaping optics providing optimal energy distributions by splitting the laser beam into several separate spots in the working plane and variable energy sharing between these spots. Various patterns, such as square, line, and rhombus, consisting of four or nine separate spots, are expected to eliminate or reduce spatter and to realize optimum temperature distributions in the melt pool and stabilizing the processes in the welding of tailored blanks, copper and aluminum parts in the production of batteries, zinc-coated steel, cladding, and LPBF. Because multimode lasers have a comparably low spatial coherence characterized by large beam parameter products or beam quality (M²) values, it is difficult to control the intensity distribution by methods other than imaging the fiber end with a collimator and a focusing objective. The proposed solution is a combination of fiber end imaging and geometrical separation of focused spots perpendicular to the optical axis using special optical components and creating a working spot as a combination of several spots. Varying the energy portions in separate spots and the distances between them make it possible to optimize common spot intensity distributions for particular applications. To ensure reliable operation with multi-kW lasers, the refractive optical components of the multispot devices are implemented from athermal optical materials characterized by insignificant thermal lensing and, hence, negligible thermal focus shift and spherical aberration. The article presents descriptions of multispot optics and examples of intensity profile measurements and application results, while the reduction in spattering was observed using multispot laser welding. It is concluded that the melt pool flows homogenize when applying several laser spots compared to a single spot. The possibility of tailoring melt pool dimensions in LPBF was shown.

Multi-keyhole separation during multi-spot laser welding of duplex steel

Separated keyholes generated during a multi-beam laser welding process were observed, analyzed, and quantified. Two high-speed cameras were utilized to capture process phenomena of bead on plate experiments, with a near vertical and a horizontal view. The films were analyzed for: the ability to form a unique keyhole for each beam, the time and location of observed fully penetrated keyhole, and other associated trends. The number of beams was correlated to fully penetrated, separate keyholes. Keyhole separations were observed to be stable while full penetration was less regular. The location of a fully penetrating keyhole correlated with the position of the stronger beam. The dynamic melt wall width separating the keyholes was measured with beam orientation and power ratios between beams having a significant impact. Beam orientation showed that the lagging inter-keyhole wall of a quad-beam process was impacted by the presence of a fully molten front in the in-line beam arrangement. For the cross-beam orientation, the lagging wall did not seem impacted by the melt front. Large power differences between leading beams for the quad-beam, in-line orientation formed a melt column in the location of the weaker beam and spattering from the column.

Backward Flux Re-Deposition Patterns during Multi-Spot Laser Ablation of Stainless Steel with Picosecond and Femtosecond Pulses in Air.

We report on novel observations of directed re-deposition of ablation debris during the ultrafast laser micro-structuring of stainless steel in the air with multi-beams in close proximity on the surface. This interesting phenomenon is observed with both 10 ps and 600 fs NIR laser pulses at 5 kHz repetition rate. Ablation spot geometries could be altered with the use of beam splitting optics or a phase-only Spatial Light modulator. At low fluence (F ~ 1.0 J cm−2) and pulse exposure of a few hundred pulses, the debris appears as concentrated narrow “filaments” connecting the ablation spots, while at higher fluence, (F ~ 5.0 J cm−2) energetic jets of material emanated symmetrically along the axes of symmetry, depositing debris well beyond the typical re-deposition radius with a single spot. Patterns of backward re-deposition of debris to the surface are likely connected with the colliding shock waves and plasma plumes with the ambient air causing stagnation when the spots are in close proximity. The 2D surface debris patterns are indicative of the complex 3D interactions involved over wide timescales during ablation from picoseconds to microseconds.

Comparison of Pain Scores Among Patients Undergoing Conventional and Novel Panretinal Photocoagulation for Diabetic Retinopathy: A Systematic Review.

PurposeTo summarize key findings from a systematic review focusing on pain as an adverse outcome of panretinal photocoagulation (PRP) among patients with diabetic retinopathy.DesignSystematic review.MethodsWe systematically searched articles in major databases from July to September 2020. Studies that compared pain outcomes of PRP among diabetic patients who underwent conventional single-spot laser (SSL), conventional multi-spot laser (MSL), and/or novel navigated laser (NNL) were included. The Cochrane RoB 2 tool and ROBINS-I tool were used to evaluate the risk of bias of the included randomized controlled trials (RCTs) and controlled clinical trials (CCTs), respectively.ResultsWe included 13 RCTs and 4 CCTs. Thirteen studies were included for Comparison 1 (Conventional SSL versus Conventional MSL), 3 studies were included for Comparison 2 (NNL versus Conventional MSL), and 3 studies were included for Comparison 3 (NNL versus Conventional SSL). A total of 783 patients and 1961 eyes were included in this review. The review showed that NNL yielded the lowest pain scores, followed by conventional MSL, then by conventional SSL.ConclusionThis review summarizes findings of multiple studies that reported pain as an adverse outcome of PRP among patients with advanced diabetic retinopathy. Data from RCTs with mostly some concerns for bias (RoB 2 tool) and CCTs with mostly moderate risk of bias (ROBINS-I tool) show benefit of using MSL over SSL, and NNL over conventional systems for PRP in diabetic retinopathy, considering pain as the primary outcome.

LASER PHOTOCOAGULATION FOR PROLIFERATIVE DIABETIC RETINOPATHY, SINGLE SPOT 532-nm vs MULTISPOT 577-nm: VERY SHORT TERM CLINICAL EFFICACY

ABSTRACT
 This study aimed to compare clinical efficacy of retinal laser photocoagulation using a 577-nm multi-spot laser with pulses of 20 ms versus conventional 532-nm single-spot laser treatment with pulses of 100 ms, on the same patient with proliferative diabetic retinopathy (PDR) during 6-weeks follow-up.
 We included 46 eyes of patients treated at the retina service of the Mexican Institute of Ophthalmology, Queretaro, Mexico. Pan-retinal photocoagulation (PRP) was performed on one eye (Group 1) using multi-spot PRP with the EasyRet® 577 diode laser (Quantel Medical, Cournon d’Auvergne, France). On the other eye (Group 2), laser treatment was performed by the conventional single spot method using the Oculight SL® 532 diode laser (IRIDEX Corporation, Mountain View, CA, The USA). The primary endpoint was absence of signs in which the disease was considered active at 6 weeks and the secondary outcomes included laser parameters, best-corrected visual acuity (BCVA), central macular thickness (CMT) at baseline, and 6 weeks and results of subjective pain analysis.
 There was no significant difference between both treatment groups regarding age, gender, BCVA or CMT at baseline. At 6 weeks, PDR activity was similar between the groups (47.8 % versus 56.5%; p =0.55). No significant difference in CMT and BCVA was observed between the groups throughout the study period. Patient-reported pain scores were similar between the groups (5.0 versus 5.8; p = 0.30). However, total time of procedure was significantly shorter in group 1 (12.9 minutes [min] versus 22.3 min; p < 0.001). No major adverse events were identified
 We concluded that laser photocoagulation of the retina with the use of the multi-spot technology in patients with PDR has similar short-term efficacy to that of conventional single spot retinal photocoagulation. The multi-spot laser required less time to complete the procedure with more spots delivered to compensate its lower fluency, showing similar patient tolerance.
 

Theoretical background of light-emitting diode total internal reflection fluorescence microscopy and photobleaching lifetime analysis of membrane-associated proteins-Part II.

The selective microscopic imaging of the plasma membrane and adjacent structures by total internal reflection fluorescence (TIRF) microscopy is a versatile and frequently used technique in cell biology. A reduction of imaging artifacts in objective-type TIRF microscopy can be achieved by circular or multi-spot laser illumination or by using noncoherent light sources that are projected into the back focal plane as a light annulus. Light-emitting diode (LED)-based TIRF excitation is a recent advancement of the latter strategy. While some basic principles of LED-TIRF remain the same as in laser-based methods, the calculation of penetration depth, the flatness of illumination and the amount of available illumination power differ. This study provides the theoretical framework for the construction and adjustment of LED-TIRF. Using state-of-the art high power LED emitters, LED-TIRF achieves excitation efficiencies that are comparable to laser-based systems and homogenously illuminate the entire field of view, thus, allowing variation of the penetration depth or quantitative photobleaching-assisted imaging protocols. Using autofluorescent transmembrane, soluble and membrane-attached fusion proteins, we provide examples for a photobleaching-based assessment of the exchange kinetics of proteins within living human endothelial cells.

PASCAL Laser Produces Less Pain Responses Compared to Conventional Laser System During the Panretinal Photocoagulation

Background: Majority of patients experience pain during complete the panretinal photocoagulation (PRP). Laser photocoagulation delivery progressed with the introduction of pattern-scanning laser systems (PASCAL). Shorter pulse duration and choroidal penetration are believed to reduce pain during laser treatment. Objective: The purpose of this study was to assess pain response in patients with proliferative diabetic retinopathy (PDR) who underwent either PASCAL or conventional laser. Subjects and Methods: Eighty eyes with newly diagnosed proliferative diabetic retinopathy were randomly divided in to two groups each composed of 40 eyes: group (A) in which patients were received standard argon laser panretinal photocoagulation and group (B) in which patients were received pattern scan multispot panretinal photocoagulation. Results: Mean pain scores were 0.515 ±0. 834 in the PASCAL laser and 0.128 ±...1 in the conventional laser group. Numerical pain score was statistically significant higher in conventional group than in PASCAL group (p<0.001). Conclusion: It could be concluded that pattern scan multispot laser PRP was associated with more patient comfort compared to conventional PRP.

PASCAL Laser Produces Less Pain Responses Compared to Conventional Laser System During the Panretinal Photocoagulation

Background: Majority of patients experience pain during complete the panretinal photocoagulation (PRP). Laser photocoagulation delivery progressed with the introduction of pattern-scanning laser systems (PASCAL). Shorter pulse duration and choroidal penetration are believed to reduce pain during laser treatment. Objective: The purpose of this study was to assess pain response in patients with proliferative diabetic retinopathy (PDR) who underwent either PASCAL or conventional laser. Subjects and Methods: Eighty eyes with newly diagnosed proliferative diabetic retinopathy were randomly divided in to two groups each composed of 40 eyes: group (A) in which patients were received standard argon laser panretinal photocoagulation and group (B) in which patients were received pattern scan multispot panretinal photocoagulation. Results: Mean pain scores were 0.515 ±0. 834 in the PASCAL laser and 0.128 ±...1 in the conventional laser group. Numerical pain score was statistically significant higher in conventional group than in PASCAL group (p<0.001). Conclusion: It could be concluded that pattern scan multispot laser PRP was associated with more patient comfort compared to conventional PRP.

A multi-spot laser induced breakdown spectroscopy system based on diffraction beam splitter.

A quick simultaneous multispot laser induced breakdown spectroscopy (LIBS) system has been proposed. The basic idea is to combine the Diffraction Beam Splitter (DBS) with the linear-to-linear fiber bundle. The DBS divided the incident laser beam into five sub-beams, and then, a lens focused the incident sub-beam to produce a plasma array, where the distance between the neighbor subplasma was constant and the plasma emission was imaged on the fiber bundle. Each ablated spot on the sample generated the corresponding spectroscopy signals, which were collected by the defined fibers of the fiber bundle, propagated to the spectrograph slit, and then analyzed by the intensified charge-coupled device (ICCD) detector, where the two-dimensional capability of the charge-coupled device detectors was explored for the spectroscopy and position analyses. The five spectroscopy ribbon presented on the ICCD corresponded to the plasma radiation of the five ablated spots. The feasibility of a simultaneous multipoint spectroscopy detection at a single pulse ablation was confirmed by subjecting to the spectroscopy analyses of a copper plane, layered material, and magnesium-molybdenum mixture. The multispot LIBS system can be used in the ejecta research of detonation physics, fluid physics, and so on.

A multi-spot laser system for retinal disorders treatment: Experimental study

Laser has many uses in ophthalmology depending on its interaction with the different layers of the eye. Laser photocoagulation techniques are used to manage many retinal disorders such as Diabetic Retinopathy by stopping the progress of the disease and prevent blindness through applying small burns on the retina to prevent the severe bleeding of the retinal blood vessels. This treatment procedure requires photocoagulation of the entire peripheral retina in order to save central vision. However, for each eye, it requires several thousands of laser shots that could be achieved in several hours divided over many treatment sessions. Instead, sending a pattern of laser spots could minimize the time required to photocoagulate the retina, hence, the photocoagulation process could be achieved through less treatment sessions, which is needed due to the increasing number of patient and relative shortage of ophthalmologists worldwide. In this work, a technique for multi-spot laser delivery system that can send a desirable pattern of laser spots to the retina in one shot was experimentally implemented and investigated. The optical setup utilized the application of liquid crystal display as a two dimensional array optical switch allowing laser spots to pass through it according to a predetermined pattern providing promising results as a multi-spot laser system to minimize treatment sessions and human errors.

Comparison of 577-nm Multispot and Standard Single-Spot Photocoagulation for Diabetic Retinopathy

Objective: To compare two different laser strategies of panretinal photocoagulation for diabetic retinopathy. Methods: Single-center, randomized study including 41 eyes treated with 577-nm multispot laser with a 20-ms pulse duration (group 1) or a 532-nm single-spot laser with a 100-ms pulse duration (group 2). The outcomes included best-corrected visual acuity (BCVA) and imaging changes at baseline, 6 and 12 months, laser parameters, and results of subjective pain analysis. Results: At 12 months, the treatments did not differ significantly in BCVA, central retinal thicknesses (CRTs), improved macular edema, vitreomacular interface changes, patient-reported pain scores, or angiographic responses. Group 1 had significantly fewer treatment sessions but used more laser spots (p < 0.001). Conclusion: The multispot laser required fewer applications with more spots delivered to compensate for lower fluency, showing similar patient tolerance to single-spot laser. Both groups maintained the initial visual acuities and CRTs; about 50% of cases had vitreomacular interface changes and improved macular edema, with similar angiographic improvements after 12 months.

Retinal function in eyes with proliferative diabetic retinopathy treated with intravitreal ranibizumab and multispot laser panretinal photocoagulation.

To compare retinal function changes in eyes with proliferative diabetic retinopathy (PDR) after intravitreal ranibizumab (IVR), combined or not with conventional (ETDRS) or multispot laser panretinal (PASCAL) photocoagulation (PRP). This study included laser-naive PDR patients that required PRP. Eyes were randomly and prospectively assigned to receive IVR or IVR combined with PASCAL or EDTRS. PRP was performed at baseline in 1 (PASCAL) or 2 (ETDRS) sessions. In eyes with macular edema, macular short pulse grid laser was associated with IVR at baseline and IVR was repeated monthly or quarterly if neovascularization was detected on angiography. Comprehensive ophthalmological evaluations, including SD-OCT, were performed at baseline and every 4weeks after treatment. Full-field electroretinography (ERG: extended ISCEV standard) was performed at baseline and at 12, 24 and 48weeks. IVR = 13, PASCAL = 15 and ETDRS = 15 eyes finished 48-week follow-up. There was a statistically significant BCVA improvement of 0.1-0.3 logMAR in all groups, and fluorescein angiography leakage area (FLA) reduced in 56%, 73%, and 73% from baseline for ETDRS, IVR and PASCAL, respectively, up to 48weeks without significant differences between groups (p > 0.05). A significant a- and b-wave amplitudes reduction was observed for dark- and light-adapted ERG for ETDRS and PASCAL, but only minor dark-adapted b-wave reduction was found for IVR, up to 48weeks. As an example, at week 48, combined response b-wave amplitude reduced in 181.5 ± 31.4µV, 128.0 ± 27.9µV and 82.4 ± 15.2µV for ETDRS, PASCAL and IVR (p < 0.05 each group), respectively. No significant difference was observed between ETDRS and PASCAL for any ERG parameter. IVR combined with single or multiple spot PRP causes similar retinal function impairment during 48weeks of observation, while IVR alone seems to be similarly effective controlling FLA without changing retinal function.

Comparison between multispot laser and conventional laser in the treatment of diabetic clinically significant macular edema

Objectives The purpose of this study was to assess the safety and efficacy of multispot laser and conventional laser in the treatment of nonproliferative diabetic retinopathy with clinically significant macular oedema (CSME) in relation to the visual outcome, central macular thickness (CMT) using optical coherence tomography, and presence of adverse events. Patients and methods This prospective randomized study included a total of 50 eyes from the research institute of ophthalmology in 2015 that were divided into two groups of 25 patients each. Group A patients underwent focal or modified grid macular laser photocoagulation using green laser 532 nm. Group B patients underwent focal or modified grid macular laser photocoagulation using multispot laser photocoagulation Valon TT. Inclusion criteria were as follows: type II diabetes and clinically significant macular edema. Best-corrected visual acuity (BCVA), optical coherence tomography readings, intraocular pressure (IOP), and adverse events were recorded preoperatively and at 1 week, 1 month, and 3 months postoperatively. Results The mean preoperative BCVA in conventional laser was 0.294 ± 0.17 decimal and that in multispot laser was 0.30 ± 0.21. The mean BCVA 3 months after laser in group A was 0.4820 ± 0.244 decimal (P = 0.001) and that in group B was 0.50 ± 0.20 (P = 0.001). The mean preoperative CMT in group A was 375.92 ± 65.69 μm and that in group B was 361.0 ± 50.400 μm. The mean CMT 3 months after laser in group A was 314.44 ± 85.94 μm (P = 0.001) um and that in group B was 0322.67 ± 57.50 μm (P = 0.001). The multispot system parameters used a higher power of 155 ± 90.1 mW (P = 0.001) compared with the conventional laser to produce the same therapeutic visible effect. Conclusion Multispot system was safe, rapid, and effective in the treatment of clinically significant macular edema in short-term follow-up periods and had a short exposure time. Although the short pulse duration of the multispot system necessitated the use of a higher power, it was not associated with adverse effects.