Laser Power Research Articles

Prediction of laser-induced breakdown in sub-micron-thick dielectric targets for laser-ion acceleration

Abstract In laser-ion acceleration experiments, the interaction of the rising flank of a high power laser pulse with the target can cause pre-ionization and subsequent target pre-expansion long before the arrival of the main laser peak. Exact knowledge of this target pre-expansion is required in order to understand the laser-plasma acceleration mechanisms with the help of numerical simulations.
For dielectric targets, the starting point of target pre-expansion is characterized by the point in time at which the target undergoes laser-induced breakdown (LIB). In this work, we present a method to determine the time of LIB in sub-micron-thick Formvar targets during interaction with a specific high-power laser pulse. The required pulse-duration-dependent LIB threshold of Formvar is measured in a dedicated experiment. A comparison of LIB threshold to previously published data facilitates a generalization to other wide-band-gap dielectric targets for laser-ion acceleration.

The mechanical properties of aged PA-12 FS3300PA powder: influence of layer thickness, sintering orientations, and laser power

Abstract This research investigates the influence of layer thickness, laser power, and sintering orientation on the mechanical properties of aged Polyamide-12 (PA-12) FS3300PA using the Selective Laser Sintering (SLS) 3D printing method. Specimens were sintered with three different layer thicknesses, laser powers, and sintering orientations using SLS. The study also aimed to examine the resulting powder morphology, mechanical properties, and tensile fracture behaviors of the aged (more than eight continuously sintering cycles) and virgin FS3300PA powders. The specimens divided into ten groups: nine groups of aged powder and one group of virgin powder as a benchmark. The nine groups of aged powder were sintered with three different layer thicknesses (0.07 mm, 0.12 mm, and 0.15 mm), laser powers (65 W, 70 W, and 75 W), and orientations (YZY 0°, YZY 90°, and XYY 0°). The selections of these laser power and layer thickness values for the sintering setting are due to machine and material parameter limitation. The results from these parameters then compared with those of the virgin powder, which sintered using the parameters provided by the manufacturer, in terms of powder morphology, mechanical properties, and tensile fracture behaviours. Observation made using scanning electron microscope (SEM) revealed that there were not many changes in shape, size, and distribution between the virgin and aged powder, but slightly larger sizes and the presence of cracks found in the aged powder. The tensile strength, elongation at break value, and Young’s modulus all shared a similar trend, increasing with higher laser power but decreasing with increased layer thickness. Regarding the fracture morphologies, the number of pores and dimples decreased with increased laser power but increased with thicker layer thickness. There was also the occurrence of un-molten powder, especially in specimens sintered at the YZY 90° orientation with lower laser power and thicker layer thickness.

Experimental study of NiTi alloy cardiovascular stent formed via SLM

Selective laser melting (SLM) has garnered significant attention in the manufacturing of cardiovascular stents due to its potential for fabricating customized stents with intricate geometries that meet clinical requirements. This study aims to optimize the SLM parameters for NiTi stents to achieve minimal porosity and surface roughness, and investigate the biocompatibility and compression tests of SLMed stents. Firstly, the single-factor experiments of laser power, scanning speed and hatch spacing are conducted, respectively. Subsequently, a Box-Benhnken experimental was employed to establish regression prediction models for porosity and surface roughness using response surface methodology (RSM). The results show that scanning speed is the most influential factor on porosity, while laser power significantly affects surface roughness. The optimized parameter combination with minimum porosity of 0.165% and surface roughness of 6.17 μm as follows: laser power of 156W, scanning speed of 712mm/s, and hatch spacing of 0.9mm. The relative errors of them are 0.19% and 0.8%, respectively, indicating that the regression model possesses good prediction ability. Additionally, the corrosion rate and nickel ion release gradually increase with the immersion time, reaching the highest corrosion rate of 2.46g/m² and nickel ion release of 1.08μg after 42 days. Besides, the SLMed stent demonstrated good recovery ability in the compression test. The findings promote the utilization of SLM in the manufacturing of NiTi cardiovascular stents for medical implant applications.

Realizing multimodal lithography effects by adjusting laser exposure power ranges for TeOx inorganic photoresist

Abstract Suboxide chalcogenide thin films like TeO x are promising inorganic lithography materials. Different from previous reports of single-mode lithography based on TeO x films at low laser power, this study proposes multimodal lithography effects at low, medium, and high laser power ranges. The TeO x films were fabricated by reactive magnetron sputtering, exhibiting super smooth surface with an RMS 0.33 nm. The lithographic performance was researched using a laser direct writing system with a wavelength of 780 nm. The experiment results showed that different kind of lithographic patterns were achieved by changing laser power ranges. At low exposure powers (5 mW to 9 mW), TeO x film transforms from amorphous to crystalline, generating patterns with single-trench since only the crystalline state dissolves in alkaline developers. At medium exposure powers (10 mW to 15 mW), the center of the laser spot that has greater power turns the film from amorphous to crystalline and then back to amorphous due to the rapid quenching process, while the outer region cools slowly to form crystalline, resulting in the patterns with double-trenches, with feature size 119 nm (about 1/7 λ). At high exposure powers (>16 mW), the laser power is capable of ablating the TeO x film, resulting in the ablation and redeposition patterns. Therefore, multimodal lithographic nano-patterns on the same TeO x photoresist film can be realized with only one lithography process by precisely manipulating the laser power ranges, which has significant implications in the fields of nano-manufacturing and optical storage.

Hydrophobic/hydrophilic surfaces constructed using laser spraying: A new route

Hydrophobic/hydrophilic coatings are widely applied in healthcare, construction, and electronic devices. However, low-cost preparation of coatings is a challenge because they are often associated with complex procedures and adverse environmental impacts. Therefore, an innovative low-cost and environmentally friendly laser spraying technology was employed to fabricate hydrophobic and hydrophilic Ni coatings. The wettability of the coatings was regulated by systematically varying laser power and substrate temperature. The Ni particles presented spherical morphology, low oxidation rate and low coverage rate (4%) with a laser power of 3000 W and room temperature substrate, yielding a hydrophobic coating with a water contact angle of 125.9±17.2°. Conversely, Ni particles exhibited oblate spherical morphology, higher oxidation rate, higher coverage rate (95%) and a porous structure with a laser power of 5400 W and a substrate temperature of 700°C, resulting in a hydrophilic coating with a water contact angle of 8.4±1.2°. These findings demonstrate a novel approach for tailoring the wettability of the Ni coatings, offering new insights into the fabrication of functional coatings for various applications.

Effects of wire feeding direction on the deposition characteristics of 316L stainless steel in laser-directed energy deposition

This study investigates the effect of wire feeding direction on the microstructure of 316 stainless steel during the laser-directed energy deposition (L-DED) process. The process parameters were optimised by varying the scan speed, laser power, and wire feed rate to identify a common parameter set for all feed directions to give desired weld bead geometries. The identified process parameter window has shown that the conduction mode is preferred over the balling and keyhole modes. Comprehensive microstructural characterization using optical and electron microscopy has revealed that for the same parameters, the front wire feed had higher penetration, while the back wire feed had a wider bead with optimal penetration. The current findings are of significance for advancing wire-L-DED additive manufacturing for more complex component designs.

Light-propelled dimeric micro-rotor in a binary critical mixture

Industrial motors produce either linear or rotational motion, and enabling these engines on micrometer scales would have significant technological implications in the biomedical, biochemical, nanoscience, and nanotechnology areas. In this paper, we report a colloidal dimeric micro-rotor consisting of a pivot particle (isotropic dielectric particle) joined to a carbon Janus particle (anisotropic particle) embedded in a critical mixture. The two particles forming this dimer are trapped and illuminated by an optical tweezer, respectively. The carbon Janus particle heats its surroundings, producing a demixing flow that results in directed rotational motion. The pivot ensures the stability of the dimer’s rotation motion, allowing for a clean circular trajectory with low dispersion between cycles. This system converts thermal energy from the absorption of light by the carbon Janus particle into mechanical rotational work. By adjusting the laser power input energy, we obtained rotational work values ranging from 3300 to 270 kBT per cycle. However, there is a limit in the laser power that induces rotation, which depends on the balance between trapping and demixing forces required for stable rotation. This paper provides an efficient method to construct a rotational micro-rotor with a stable motion (standard deviation = 0,03 µm) for nano and micro devices.

Corrosion and Microhardness Behavior Improvement of 316L Stainless Steel via Fiber Laser Surface Treatment

This study investigated how fibre laser surface treatment affects stainless steel 316L’s microhardness and corrosion resistance. The laser parameters utilized in this investigation were four different readings of laser power applied at a constant frequency and scanning speed to stainless steel 316L specimens. A digital micro-Vickers hardness tester was used to measure the microhardness of the samples before and after laser treatment. The TAFEL cyclic potentiodynamic polarization technique was employed to study corrosion behaviour. The microstructure of the base metal and the effect of laser power were investigated using optical microscopy. The phases before and after laser treatment were identified through X-ray diffraction, and the cross section of the heat-affected zones and the molten pool’s depth were examined using a scanning electron microscope. Results revealed that laser treatment affected microstructural transitional phase alterations. Compared with the average microhardness of the base metal, the microhardness of the laser-treated specimens improved to 78.23% as the laser power increased. The increase in microhardness considerably enhanced corrosion resistance to 36.13% relative to that of the base metal.

Optothermal trapping of microparticles near an absorbing reflective film with an annular beam.

Optothermal manipulation technologies trap and manipulate microparticles under a light-controlled temperature gradient. In this paper, we demonstrate the possibilities of optothermal trap, which is generated by an annular beam irradiating on an absorbing reflective film to capture the microparticles. The particles are subjected to thermal and optical gradient forces. First, we investigate the particle trapping near a non-absorbing reflective surface to understand the action of the optical force of annular beam. The results show that the optical force cannot trap the particles near a reflective surface. Second, an annular beam is generated by Gaussian beam shaping with the aid of axicons, which is then used to irradiate and heat a gold film to create an optothermal trap. The induced thermal gradient and thermal convection can bind the particles in the center of the annular spot. The trapping stiffness of the optothermal trap is 8.1 ± 2.9 fN/μm at a laser power of 100 mW.

Enhancing Predicted Visual Acuity After SmartSight Lenticule Extraction: Identifying Key Factors With Machine Learning.

To develop a predictive model aimed at assessing the likelihood of improvement in corrected distance visual acuity (CDVA) for patients undergoing lenticule extraction using the SmartSight system from SCHWIND eye-tech-solutions. This model evaluates the effectiveness and weight of various clinical and procedural parameters in predicting enhancements in visual acuity. Data from 1,262 eyes treated with the SmartSight system, encompassing 86 features, were analyzed. Regression and classification techniques were employed to estimate the probability of CDVA gain, ensuring robust results by comparing different methods. The dataset was divided into training (70%, 883 treatments) and testing (30%, 379 treatments) subsets to ensure comprehensive model evaluation using machine learning methods. Feature significance was determined via analysis of variance and principal components analysis to identify impactful parameters. Three principal components accounting for more than 70% of the data variance were identified. The first component was primarily linked to system settings, whereas the second and third components were associated with patient gender and laterality. Factors significantly influencing CDVA improvement included a higher spot-to-track distance ratio, tighter track distance, lower pulse energy, lower average laser power, larger spot distance, greater cap thickness, and lower dosage. These variables were ranked based on their impact on CDVA enhancement. Using low-energy asymmetric spacing for lenticule extraction with the SmartSight system is safe and effective. This approach improves visual outcomes for patients undergoing treatment for myopic astigmatism, offering a reliable method for predicting CDVA improvements. [J Refract Surg. 2024;40(12):e974-e984.].

Influence of Laser Power on Microstructure and Performance of SiC/Ti Composite Fabricated by Selective Laser Melting

Influence of Laser Power on Microstructure and Performance of SiC/Ti Composite Fabricated by Selective Laser Melting

InGaAs/GaAs metamorphic buffer for laser power convterers applications

InGaAs/GaAs metamorphic buffer for laser power convterers applications

Surface Modification of Si3N4 via Silane Coating and Oxidation for Photocurable Slurry Preparation

To address the issues of low curing depth and high viscosity in VPP slurries caused by the high refractive index and hydrophilic surface of silicon nitride (Si3N4), this study proposes a novel surface modification method. The process starts with the pre-coating of Si3N4 powder using the silane coupling agent KH570. This is followed by an oxidation step that forms a uniform SiO2 layer on the powder surface, effectively reducing the refractive index mismatch between Si3N4 and the resin, as well as minimizing light scattering. The KH570 pre-coating also protects the Si3N4 lattice, mitigating oxidation-induced damage and preserving structural integrity. Subsequently, the Si3N4 powder undergoes further modification with the silane coupling agent KH560 to enhance the slurry’s flowability and stability. Using this three-step method of pre-coating, oxidation, and surface modification, a Si3N4 slurry with 45 vol.% solid content was successfully prepared. The slurry’s viscosity decreased by 20-30%, and under a laser power of 1200 mW, the curing depth increased by 52.9%, reaching a value of 192.7 μm with a viscosity of 7.69 Pa·s (at a shear rate of 30 s⁻1 and 47.8 rpm). This approach enables the fabrication of high-quality Si3N4 ceramic components with intricate geometries.

Study on PCD tool wear in pulsed laser assisted turning Al-50wt % Si alloy

Al-50wt % Si alloy is widely used in aerospace, automotive, electronic packaging and other fields due to its excellent material properties. However, the presence of reinforced particle phase differing in hardness from the alloy matrix phase leads to significant tool wear during turning with PCD tools. Therefore, this paper proposes a pulsed laser assisted turning (PLAT) method combining pulsed laser with conventional turning, which has unique advantages in reducing PCD tool wear. The effects of laser power, pulse width and frequency on tool wear during PLAT were studied by comparative experiments. And the potential mechanism of PLAT to reduce tool wear was revealed by finite element simulation. The results shown that PLAT effectively reduces PCD tool wear compared with conventional turning (CT). The increase of laser pulse width will aggravate tool wear. While, the increase of laser pulse frequency will reduce tool wear. Temperature is the main factor affecting the wear form. The tool mainly experiences abrasive wear at low temperature. However, the predominant type of tool wear shifts to adhesion as the increasing temperature. At the same time, EDS analysis shows that the rise in temperature results in an elevation of the O element content within the wear region, which proves that temperature is also the decisive factor affecting oxidative wear. This study provides valuable insights into actual machining involving Al-50wt % Si alloys and gives strategies for reducing PCD tool wear using PLAT.

A Study on the Carbon Dioxide Laser

Abstract: One of the first gas lasers to be created was the carbon-dioxide laser (CO2 laser). One of the most practical kinds of lasers, it was created in 1964 by Bell Labs' Kumar Patel [22]. The most powerful continuous-wave lasers on the market right now are carbon-dioxide lasers. Additionally, they are quite efficient; the output power to pump power ratio can reach 20%. The primary wavelength bands of the infrared light beam produced by the CO2 laser are 9.6 and 10.6 micrometers (μm). [22] In order to improve its performance, a carbon dioxide laser uses carbon dioxide as its main gain medium. Nitrogen (N2), helium (He), and occasionally hydrogen (H2), water vapor, oxygen, or xenon (Xe) are added. This laser works by energizing the gas mixture to produce laser light by promoting the emission of radiation by an electrical gas discharge. In carbon dioxide lasers, the electrical gas discharge can be powered by radio frequency (RF), direct current (DC), or alternating current (AC). The wavelength of the light emitted by these lasers is 10.6 micrometers. In dermatology, they are frequently used for operations like wrinkle reduction, scar removal, and sun damage treatment. Furthermore, for accurate cutting and tissue removal, carbon dioxide lasers are employed as surgical instruments in specialties such as neurosurgery and gynecology.[24]

Tuning pores and mechanical properties for the heterogeneous interface of laser directed energy deposited IN718/316L laminate via in-situ laser surface remelting

In the past decades, laser directed energy deposition (L-DED) of multi-material attracts much attention for the integration of structure and performance. However, interfacial pores and limited mechanical properties are still bottlenecks. The present study introduces the in-situ laser surface remelting (LSR) treatment to L-DED of IN718/316 L laminate. During the LSR process, the continuous-wave (CW) near-infrared fiber printing laser rescans the whole surface after completely depositing the bottom material. When the bottom material was selected as 316 L and IN718, the pores around the heterogeneous interface were obviously eliminated and the proportion of high angle grain boundaries (HAGBs) was respectively lifted by 85.1 % and 149.1 % with slightly reduced average grain diameter after LSR treatment. Eventually, 8.5 % and 58.9 % increase in the elongation were respectively achieved. According to the numerical investigation, the “pinch-off” of bubble is observed during LSR process for the first time and the necking is enhanced with increased remelting laser power when the bottom material is IN718. Furthermore, the pore below the molten pool is prone to enlarge with stress concentration. This work can provide a novel guidance for the defect-free AM-built laminate.

Improving signal-to-noise ratio of Raman measurements based on ensemble learning approach.

Raman spectroscopy is an extensively explored vibrational spectroscopic technique to analyzethebiochemical composition and molecular structure of samples, which is often assumed to be non-destructive when carefully using proper laser power and exposure time. However, the inherentlyweak Raman signal and concurrent fluorescence interference often lead to Raman measurements withalow signal-to-noise ratio (SNR), especially for biological samples. Great efforts have been made to develop experimental approaches and/or numerical algorithms to improvetheSNR. In this study, we proposed an ensemble learning approach to recover and denoise Raman measurements withalow SNR. The proposed ensemble learning approach was evaluated on 986 pairs of Raman measurements, each pair of which consists of a low SNR Raman spectrum and a high SNR reference Raman spectrum from the exact same fungal sample but uses 200 timestheintegration time. Compared with conventional methods, the Raman measurementsrecoveredby the proposed ensemble learning approach are more identical to high SNR reference Raman measurements, with anaverage RMSE and MAE of only 1.337 × 10-2 and 1.066 × 10-2, respectively; thus, the proposed ensemble learning approach is expected to be a powerful tool for numerically improving the SNR of Raman measurements and further benefits rapid Raman acquisition from biological samples.

Influence of ambient pressure on laser beam melting of lunar regolith simulant

The construction of a lunar base requires a huge amount of material, which cannot be entirely transported from Earth. Therefore, technologies are needed to build with locally available resources, such as the lunar regolith. One approach is to directly melt the lunar regolith on the surface and under the vacuum condition of the Moon, using laser radiation. In this article, a lunar regolith simulant is laser beam melted to two-dimensional single-layer-structures using different ambient pressures from 0.05 mbar to 2000 mbar, laser process parameters from 60 W to 100 W laser power, and 1 mm s−1 to 3 mm s−1 feed rates. Additionally, the influence of the ambient gas was investigated using argon as an air alternative. The results show that the ambient pressure on the Moon is not negligible when studying the melting processes of lunar regolith on Earth. With decreasing ambient pressure, the appearance of the melted regolith simulant varies from a shiny to a matt surface. At the highest laser energy density, the thickness of a single-layer increases from 2.6 ± 0.4 mm to 5.3 ± 0.3 mm and the porosity of the melted regolith increases from 17.2 % to 52.2 % with decreasing ambient pressure. Additionally, mechanical properties are determined using 3-point bending tests. The maximum bending strength decreases by 60 % with the increased ambient pressure from 10 mbar to 2000 mbar. Consequently, the development of in-situ resource utilization technologies, which process the lunar regolith directly on the lunar surface, must consider the ambient pressure on the Moon. Otherwise, the processes will not work as expected from the experiments in Earth-based laboratories.

Additive Manufacturing of AISI H13 Tool Steel with Combinations of Higher Laser Power and Scan Speed: Microstructural and Mechanical Properties Insights

Additive Manufacturing of AISI H13 Tool Steel with Combinations of Higher Laser Power and Scan Speed: Microstructural and Mechanical Properties Insights

Effect of Substrate Temperature on Bead Track Geometry of 316L in Directed Energy Deposition: Investigation and Regression Modeling

The optimization of process parameters in powder Directed Energy Deposition (DED) is essential for achieving consistent, high-quality bead geometries, which directly influence the performance and structural integrity of fabricated components. As a subset of additive manufacturing (AM), the DED process, also referred to as laser metal deposition (LMD), enables precise, layer-by-layer material deposition, making it highly suitable for complex geometries and part repair applications. Critical parameters, such as the laser power, feed rate, powder mass flow, and substrate temperature govern the deposition process, impacting the bead height, width, contact angle, and dilution. Inconsistent control over these variables can lead to defects, such as poor bonding, dimensional inaccuracies, and material weaknesses, ultimately compromising the final product. This paper investigates the effects of various process parameters, specifically the substrate temperature, on bead track geometry in DED processes for stainless steel (1.4404). A specialized experimental setup, integrated within a DED machine, facilitates the controlled thermal conditioning of sample sheets. Using Design of Experiments (DoE) methods, individual bead marks are generated and analyzed to assess geometric characteristics. Regression models, including both linear and quadratic approaches, are constructed to predict machine parameters for achieving the desired bead geometry at different substrate temperatures. Validation experiments confirm the accuracy and reliability of the models, particularly in predicting the bead height, bead width, and contact angle across a broad range of substrate temperatures. However, the models demonstrated limitations in accurately predicting dilution, indicating the need for further refinement. Despite some deviations in measured values, successful fabrication is achieved, demonstrating robust bonding between the bead and substrate. The developed models offer insights into optimizing DED process parameters to achieve desired bead characteristics, advancing the precision and reliability of additive manufacturing technology. Future work will focus on refining the regression models to improve predictions, particularly for dilution, and further investigate non-linear interactions between process variables.