Single Laser Spot Research Articles

Investigating the ablation threshold and morphology of spots generated on graphite electrode by femtosecond Gaussian laser pulses

This study investigates the effects of femtosecond laser irradiation on graphite, a highly sought-after material known for its exceptional chemical stability and ability to withstand extreme temperatures. The ablation threshold and surface morphology of graphite were determined using a tightly focused laser beam with varying pulse numbers and laser fluences. The results showed that the laser beam produced diverse morphological structures within different regions of a single laser spot, and the ablation threshold and surface morphology were significantly influenced by the number of pulses and the energy density of the incident laser. The study found that the ablation threshold of graphite was 107, 90, 76, and 56 ± 0.5 mJ/cm2 for 5, 50, 200, and 500 laser pulses, respectively. The resulting surface structures ranged from quasi-periodic to periodic, with varying periodicities, and the ablation debris exhibited morphologies from fine particles to long filaments. The crystal structure of the specimen was analyzed via X-ray diffraction and micro-Raman spectroscopy, with compositional analysis performed using energy-dispersive X-ray spectroscopy (EDX). Notably, a significant broadening of the Raman spectrum peaks with increasing pulse energy suggested the formation of a more disordered structure. These findings demonstrate that femtosecond laser ablation can precisely manipulate the surface morphology and nanoparticle production, presenting potential applications in fields such as nanoparticle generation and engineering surface properties like adhesion, biocompatibility, spectral reflectivity, wear resistance, and wettability.

Study on the formation mechanism of functional surface microstructure by ultrasonic vibration assisted laser processing

In this paper, a novel ultrasonic vibration-assisted laser surface processing technology is proposed for preparing microstructures on metal surfaces. Firstly, the formation mechanism of single laser spot on metal surface is analyzed, and the mathematical model of three-dimensional morphology of single crater is derived, the influence of ultrasonic vibration on the crater morphology is studied. Secondly, the influence of ultrasonic vibration on the position distribution of heat affected zone in single laser path is studied. After, the influence of ultrasonic vibration and laser scanning speed on the shape of the laser path is expressed by pushing the overlap rate between the heat affected zones. The calculation results show that the larger ultrasonic amplitude, the greater effect on the curve shape. Finally, the correctness of the calculation and simulation results is verified by experiments. It is observed that ultrasonic vibration can promote the discharge of the melt and provide a new method for changing the surface microstructures.

Circular array transducer based-photoacoustic/ultrasonic endoscopic imaging with tunable ring-beam excitation

Photoacoustic/ultrasound endoscopic imaging is regarded as an effective method to achieve accurate detection of intestinal disease by offering both the functional and structural information, simultaneously. Compared to the conventional endoscopy with single transducer and laser spot for signal detection and optical excitation, photoacoustic/ultrasound endoscopic probe using circular array transducer and ring-shaped laser beam avoids the instability brought by the mechanical scanning point-to-point, offering the dual-modality imaging with high accuracy and efficiency. Meanwhile, considering the complex morphological environments of intestinal tracts in clinics, developing the probe having sufficient wide imaging distance range is especially important. In this work, we develop a compact circular photoacoustic/ultrasonic endoscopic probe, using the group of fiber, lens and home-made axicon, to generate relatively concentrated ring-shaped laser beam for 360° excitation with high efficiency. Furthermore, the laser ring size can be tuned conveniently by changing the fiber-lens distance to ensure the potential applicability of the probe in various and complex morphological environments of intestines. Phantom experimental results demonstrate imaging distance range wide enough to cover from 12 mm to 30 mm. In addition, the accessibility of the photoacoustic signals of molecular probes in ex vivo experiments at the tissue depth of 7 mm using excitation energy of 5 mJ has also been demonstrated, showing a high optical excitation efficiency of the probe.

Spatially modulated femtosecond laser direct ablation-based preparation of ultra-flexible multifunctional copper mesh electrodes and its application.

Multifunctional electrodes possess superior properties such as high photoelectric properties and high stability. Laser manufacturing process is one of the widely used method for electrode fabrication. However, the current multifunctional electrode laser manufacturing process suffers from low fabrication speed. Here, we report a high-efficiency laser digital patterning process to fabricate copper-based flexible transparent conducting electrodes. By using a spatially modulated, one single laser spot is modulated into an array of spots with equal intensity, and the fabrication speed can be improved by more than 20 times over the traditional single pulse processing. In addition, copper mesh electrodes with a high photoelectric property have been fabricated. A transparent touch screen panel and multifunctional windows are fabricated with transparent electrodes to demonstrate their use in vehicle defogging, portable heating, and wearable devices.

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.
 

Monitoring spatially resolved trace elements in polar bear hair using single spot laser ablation ICP-MS

Elements and compounds circulating in the body are incorporated into hair as it grows. Because of this, hair analyses are increasingly being incorporated in investigations of temporal trends in e.g. hormones and diet in wildlife species such as polar bears (Ursus maritimus).For this study, guard hair (GH; mean length 62 mm) and foreleg guard hair (FGH; mean length 164 mm) were collected from 15 adult male polar bears in western Hudson Bay, Canada. Our aim was to quantify the trace elements arsenic (As), cadmium (Cd), copper (Cu), iron (Fe), lead (Pb), mercury (Hg), selenium (Se), strontium (Sr), and zinc (Zn) every 3 mm in GH and FGH using laser ablation inductively coupled plasma mass spectrometry (laser ablation ICP-MS).Quantitative data was obtained at spatial scales as small as 50 μm – the smallest laser spot diameter used. Mean trace element concentrations increased in the order Pb < As < Cd < Se < Hg < Cu < Sr < Fe < Zn for both GH and FGH (pooled across all individuals). However, mean trace element concentrations were all significantly different between GH and FGH, except for Hg. Hg concentration varied along the length of both GH and FGH; each bear exhibited a unique pattern in Hg variation along the hair. For the remaining eight trace elements, the most common pattern was that of smaller fluctuations near the base of the hair, followed by an increase towards the tip. These fluctuations in trace element concentrations were likley related to hair growth and temporal changes. In this pilot study, we found quantifying trace elements in polar bear hair using laser ablation ICP-MS to be a promising monitoring technique across multiple temporal scales.

Greatly enhanced magneto-optic detection of single nanomagnets using focused magnetoelastic excitation

Magnetization dynamics of nanomagnets directly determine the performance of magnetic storage and memory devices. Here, we report a 10-times enhancement of magnetization dynamics excitation of single nanomagnets using focused surface acoustic waves (SAWs), compared to conventional optical excitation. SAWs are generated via ultrafast optical excitation of an arc-shaped phononic grating and focused onto a single nanomagnet located at the focal spot of the grating. Thanks to the robust resonance excitation, we observe the strain-controlled ultrafast magnetization dynamics in a sub-100 nm single nanomagnet. This improved excitation efficiency was applied to exciting SAWs in four sets of gratings with different pitches using a single laser spot. This enabled selective excitation of any one of four identical nanomagnets at different frequencies simply by tuning an external magnetic field. This all-optical technique provides a method of addressing individual magnetic nano-oscillators and studying their intrinsic magnetization dynamics.

Surface modification of NiTi alloy by ultrashort pulsed laser shock peening

This research paper presents the attempt at ultrashort pulsed laser shock peening with absence of absorptive layer and confining medium which could enhance surface microhardness and the abrasion property of NiTi shape memory alloy. The average roughness values of NiTi specimen were measured on the surface, because the roughness would affect the friction resistance. The microhardness and Young's modulus were investigated at different position of single laser spot by nanoindentation technique. The pin-on-plate sliding abrasion testing were performed with different load-force (0.5 N and 2 N) for different testing time. Results showed that ultrashort pulsed laser shock peening treatment would cause a significant improvement on friction coefficient and abrasion property, which was attributed to the change of surface modification, such as roughness, microhardness, microstructure and titanium oxide layer, but the ultrashort pulsed laser shock peening treatment did not enhance its tensile strength during present research.

Simultaneous high-speed x-ray transmission imaging and absolute dynamic absorptance measurements during high-power laser-metal processing

During high-power laser metal processing, the absorbed light is intimately related to the molten metal cavity shape. For the first time, this relationship is observed directly and simultaneously by implementing state-of-the-art techniques of high-speed x-ray imaging and integrating-sphere radiometry. Experiments were performed on Ti-6Al-4V solid and powder under single spot laser illumination for laser conditions that cause keyhole formation and collapse. The data from x-ray imaging corroborates that a dramatic rise in laser absorption is due to keyhole formation. We also find that the keyhole area correlates most strongly with energy absorption followed closely by keyhole depth. Furthermore, time synchronization reveals correlations between keyhole fluctuations and sinusoidal variations in energy absorption that occur during nominally “stable” keyhole conditions. Absorption data show a 24 % periodic change in absorbed laser power at a 50 kHz frequency. The absorption peaks correlate to relatively large, open keyholes, whereas images taken at the troughs reveal keyholes with substantial undulations of the keyhole sidewalls. These observations give crucial, quantitative data for computational modeling whose aim is to predict porosity and defect formation.

Navigated Pattern Laser System Versus Single-Spot Laser System for Postoperative Laser Retinopexy

Purpose: To compare three 360°-laser retinopexy (LRP) approaches (using navigated pattern laser system, single-spot slit-lamp (SL) laser delivery and single-spot indirect-ophthalmoscope (IO) laser delivery) in regard to procedure duration, procedural pain score, technical difficulties and the ability to achieve surgical goals. Patients and Methods. Eighty-six rhegmatogenous retinal detachment patients (86 eyes) were included in this prospective randomized study. Ten patients were underwent scleral buckling procedure, 37 patients were underwent vitrectomy, 7 patients had a combined procedure, and 32 patients had silicone oil tamponade. The mean procedural time, procedural pain score (using 4-point Verbal Rating Scale), number of laser burns, and achievement of the surgical goals were compared between three groups (pattern LRP (NAVILAS laser system), 36 patients; SL-LRP, 28 patients; and IO-LRP, 22 patients). Results. In the pattern LRP group, the time needed for LRP and pain level (12.4 ± 5.4 min and 1.1 ± 0.5 scores, respectively) were statistically significantly lower, whereas the number of applied laser burns (1108.7 ± 345.5) was higher compared to those in the SL-LRP group (21.7 ± 7.6 min, 1.8 ± 0.5 scores, and 714.5 ± 219.8 burns) and in the IO-LRP group (17.0 ± 10.1 min, 1.9 ± 0.5 scores, and 408.1 ± 95.5 burns). In the pattern LRP, SL-LRP, and IO-LRP groups, surgical goals were fully achieved in 28 (77.8 %), 17 (60.7 %), and 13 patients (59.1 %), respectively (p &gt; 0.05). In the pattern LRP, SL-LRP and IO-LRP groups, the mean duration of follow-up after silicone oil removal was 6.6 ± 3.1 months, 8.1 ± 4.5 months and 7.1 ± 4.1 months, respectively (ANOVA3x, p = 0.35), with re-detachment found in 1 case (8.3 %), 2 cases (18.2 %), and 1 case (11.1 %), respectively. Conclusions. The navigated pattern approach allows improving the treatment time and pain in postoperative 360° LRP. Moreover, 360° pattern LRP is at least as effective in achieving the surgical goal as the conventional (slit-lamp or indirect ophthalmoscope) approaches with a single-spot laser.

Bioinspired Functional Surfaces Enabled by Multiscale Stereolithography

AbstractAdditive manufacturing has many advantages in creating highly complex customized structures. In this study, a low‐cost multiscale stereolithography technology that can print a macroscale object with microscale surface structures with high throughput is demonstrated. The developed multiscale stereolithography is realized by dynamic switching of laser spot size and adaptively sliced layer thickness. An optical filter based on subwavelength resonance grating is used to modify laser spot size for lasers with different wavelengths and achieves a maximum resolution of 37 µm. The multiscale stereolithography process has 4.4× throughput improvement compared with the traditional stereolithography process with a single laser spot. For proof‐of‐concept testing, artificial shark skins with microriblet features are designed and 3D printed. In pipe flow experiments, the 3D printed shark skin demonstrates almost 10% average fluid drag reduction. Artificial lotus leaf surfaces are also 3D printed to demonstrate superhydrophobic property. This new process has the potential to serve as a powerful tool that can bring bioinspired structures into real‐life applications.

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.

Photothermal generation of programmable microbubble array on nanoporous gold disks.

We present a novel technique to generate microbubbles photothermally by continuous-wave laser irradiation of nanoporous gold disk (NPGD) array covered microfluidic channels. When a single laser spot is focused on the NPGDs, a microbubble can be generated with controlled size by adjusting the laser power. The dynamics of both bubble growth and shrinkage are studied. Using computer-generated holography on a spatial light modulator (SLM), simultaneous generation of multiple microbubbles at arbitrary locations with independent control is demonstrated. A potential application of flow manipulation is demonstrated using a microfluidic X-shaped junction. The advantages of this technique are flexible bubble generation locations, long bubble lifetimes, no need for light-adsorbing dyes, high controllability over bubble size, and relatively lower power consumption.

Polarization-controlled microgroove arrays induced by femtosecond laser pulses

Using pulsed femtosecond laser irradiation, we demonstrate the creation of an array of microgrooves within a single laser spot on metals. The orientation of these grooves is not limited to being parallel to the plane of the laser beam's propagation but can orient at any angle up to 30° from parallel. We control the orientation of the microgrooves by proportionally varying the laser's polarization. Polarization, angle of incidence, and structural evolution dynamics have been thoroughly studied to help us understand this phenomenon. Our studies suggest that the formation of angled microgroove arrays is due to a feedback effect occurring between defect-focused ablation and polarization-dependent laser-induced periodic surface structures.

Flow dynamics during single- and dual-spot laser welding with one common keyhole of 321 stainless steel

The keyhole is unstable with the presence of humps at the keyhole walls during single-spot laser welding (SSLW). The keyhole stability is improved and the presence of humps is reduced during dual-spot laser welding (DSLW). The vortices present at the rear keyhole wall during SSLW disappear during DSLW. There is an upward motion of the melt flow at the rear keyhole wall and the melt flow velocity is higher along the width of the molten pool during DSLW. A sandwich specimen is constructed to investigate the effect of keyhole and melt flow dynamics on the final shape of the weld seam. The results show that DSLW produces smoother, more regular weld beads due to higher stability of the keyhole and molten pool. DSLW produces a weld seam with fewer porosities and a more homogeneous nickel distribution due to the upward motion and absence of vortices in the melt flow. DSLW produces a wider molten pool due to the higher melt flow velocity along the width of the molten pool.

Pattern scan laser versus single spot laser in panretinal photocoagulation treatment for proliferative diabetic retinopathy

Pattern scan laser versus single spot laser in panretinal photocoagulation treatment for proliferative diabetic retinopathy

Effect of dual beam laser welding on microstructure–property relationships of hot-rolled complex phase steel sheets

The work addresses microstructure–property relationships of hot-rolled complex phase steel sheets subjected to various conditions of dual beam laser welding. The article also contains a comparison between single-spot and twin-spot laser welding. Test-related joints were made using a Yb:YAG disc laser having a maximum power of 12kW and a welding head enabling the focusing of a laser beam on two spots. The tests involved investigating the effect of power distribution on the macrostructure, microstructure and mechanical properties of joints. Microscopic investigations revealed the stabilisation of some fraction of retained austenite in the intercritical heat affected zone (ICHAZ) of joints. The application of the second beam resulted in tempering-like effects in the martensite of the fusion zone and in the HAZ, favourably reducing the hardness of the joint. The use of bifocal welding enabled the obtainment of a 10% hardness reduction in the fusion zone as against single-spot laser beam welding.

Comparison of therapeutic effect of micro-pulse laser and conventional laser on diabetic macular edema

Objective To compare the therapeutic effect of micro-pulse laser, single-spot laser and pattern scan laser for diabetic macular edema(DME). Methods Total of 120 eyes of 60 patients who were confirmed as preproliferative diabetic retinopathy or IV phase proliferative diabetic retinopathy complicated with clinically significant macular edema were included. These patients were randomized divided into the micro-pulse group with 40 eyes of 20 patients, the single-spot laser group with 40 eyes of 20 patients and the pattern scan laser group with 40 eyes of 20 patients.The patients in micro-pulse group underwent micro-pulse laser therapy in macular region , the single-spot laser group underwent macular laser grid photocoagulation therapy by single-spot laser, the pattern scan laser group underwent macular laser grid photocoagulation therapy by pattern scan laser.The BCVA, central macular thickness(CMT) and mean sensitivity(MS) of all patients were examined before and after the treatment. The changes in BCVA, CMT and MS at 6 months after treatment were observed and compared among the groups. Results At 6 months after the treatment, the BCVA of micro-pulse group increased more significantly compared to that before treatment(P 0.05). At 6 months after the treatment, the CMT of micro-pulse group, single-spot laser group and pattern scan laser group decreased significantly compared to those before treatment(P 0.05). At 6 months after the treatment, the MS of micro-pulse group increased significantly compared to that before treatment(P<0.05), the MS of single-spot laser group and pattern scan laser group decreased significantly compared to those before treatment(P<0.05), the MS of the three groups showed statistical difference (P<0.05). Conclusion Micro-pulse laser, single-spot laser and pattern scan laser therapies on DME can effectively reduce CMT and alleviate macular edema, micro-pulse laser therapy on DME also increase BCVA and MS, and improve visual function.Single-spot laser and pattern scan laser therapies can not improve visual function. Key words: Macular edema, diabetic; Micro-pulse laser; Laser coagulation; Effect, therapeutic

Simulation of surface cracks measurement in first walls by laser spot array thermography

The inspection of surface cracks in first walls (FW) is very important to ensure the safe operation of the fusion reactors. In this paper, a new laser excited thermography technique with using laser spot array source is proposed for the surface cracks imaging and evaluation in the FW with an intuitive and non-contact measurement method. Instead of imaging a crack by scanning a single laser spot and superimposing the local discontinuity images with the present laser excited thermography methods, it can inspect a relatively large area at one measurement. It does not only simplify the measurement system and data processing procedure, but also provide a faster measurement for FW. In order to investigate the feasibility of this method, a numerical code based on finite element method (FEM) is developed to simulate the heat flow and the effect of the crack geometry on the thermal wave fields. An imaging method based on the gradient of the thermal images is proposed for crack measurement with the laser spot array thermography method.