Number Of Laser Pulses Research Articles

PLLA honeycombs activated by plasma and high-energy excimer laser for stem cell support

In this study, we constructed and activated honeycomb structures on perfluorinated substrates subjected to KrF laser treatment (wavelength 248 nm). We selected the biopolymer poly L-lactic acid (PLLA) as the honeycomb material, which was dissolved in a mixture of chloroform/methanol. A micropattern of a plasma-treated perfluorethyleneperopylene (FEP) substrate was prepared by improved phase separation during dip-coating. The PLLA micropattern was subsequently treated with an excimer laser with a laser fluence of 10 mJ.cm-2 and with a different number of laser pulses. Alternatively, plasma exposure can be used as a secondary treatment. The surface morphologies of the pristine and laser-treated PLLA patterns were studied using atomic force and scanning electron microscopy. The surface chemistry was analyzed using energy-dispersive spectroscopy and X-ray photoelectron spectroscopy. In addition, the metabolic activity of adipose stem cells was evaluated using the MTS test, and cell numbers in selected samples were determined. The morphology of cells growing in the honeycomb-like pattern was studied in detail using fluorescence microscopy. In all, we used a combination of honeycomb pattern (HCP) laser treatment and plasma treatment to construct an optimal scaffold for adipose stem cell culture.

The effect of the age at the time of targeting a lead implantation on the difficulty with the transvenous lead extraction technique

Abstract Background In transvenous lead removal procedures, the number of years since the lead implantation is an indicator of procedural difficulty and complications. However, even with the same number of years since the lead implantation, we considered the possibility that a younger age at the time of the implantation (AoI) would increase the difficulty of the procedure. Objective To elucidate the procedural difficulty in the transvenous lead extraction procedure according to the age at the time of targeting the lead implantation. Method A total of 471 consecutive transvenous lead extraction cases were analyzed. The patient AoI of the oldest lead in extraction procedure cases was divided into two groups: those younger than 60 years (implant age <60 yrs old: AoI<60) and those older than 60 years (implant age ≧60 yrs old: AoI≧60). The analysis was conducted by the number of years since the lead implantation (<10 years: group A, 10 to 20 years: group B, and >20 years: group C). Results The number of AoI<60 and AoI≧60 patients were 60 and 254 (Group A), 51 and 56 (Group B), and 41 and 9 (Group C). The patient age significantly differed among the groups between an AoI<60 and AoI≧60 (group A: 51.7 vs. 77.1; P<0.001, group B: 61.6 vs. 83.1; P<0.001, group C: 71.2 vs. 88; P<0.001). But the oldest dwell time (years) was similar for all groups (group A: 4.6 vs. 4.2; P=0.324, group B: 14.2 vs. 13.5; P=0.148, and group C: 25.7 vs. 22.6; P=0.097). The complete removal rate (group A: 97.7% vs. 98.4%; P=0.722, group B: 90.4% vs. 93.3%; P=0.567, and group C: 78.05 vs. 90.95; P=0.337) and major complication-free rate (group A: 98.8% vs. 100%; P=0.391, group B: 96.2% vs. 100%; P=0.125, and group C: 90.2% vs. 100%; P=0.281) were not statistically significant in all groups but were higher for an AoI≧60. An AoI<60 resulted in a longer procedure time (group A: 78.4 min. vs. 65.3 min.; P=0.006, group B: 96.0 min. vs. 72.3 min.; P=0.002, and group C: 100.9 min. vs. 94.8 min.; P=0.709), longer fluoroscopy time (group A: 12.0 min. vs. 10.2 min.; P=0.247, group B: 19.2 min. vs. 11.6 min.; P=0.017, and group C: 22.2 min. vs. 16.0 min.; P=0.008), and higher number of laser pulses (group A: 779.6 vs. 433.7; P=0.002, group B: 2089.6 vs. 1032.9; P=0.017, and group C: 1509.3 vs. 831.5; P=0.201) in all groups. Conclusion This study suggested that the difficulty of transvenous lead extraction procedures may increase with a younger AoI, even if the lead dwelling time is the same.

Temperature Effects on the Optical Properties of Bismuth Nanoparticles Prepared by PLAL for Antibacterial Activity

Bismuth nanoparticles (Bi NPs) constitute a promising technology for combating infectious illnesses and bacterial resistance to antibacterial treatments. Bi NPs were synthesized by Pulsed Laser Ablation in Liquid (PLAL) using a 532 nm second-harmonic generation Nd:YAG laser. Bi NPs samples were prepared in 10, 35, 50, 75, and 90 ˚C water for various laser energies and number of laser pulses. Ultraviolet-visible (UV-Vis) spectra measurements revealed a characteristic plasmonic absorption band indicative of metallic bismuth nanosized particles. Field emission scanning electron microscopy (FESEM) analysis showed that the water temperature during the ablation process affected the size and morphology of Bi NPs. The average Bi NP size at 60 ˚C was 28 nm, considerably smaller than the 55 nm average observed at 10 ˚C. The antimicrobial properties of Bi NPs against two opportunistic pathogens, E. coli and S. aureus, were assessed. For S. aureus, the inhibition zone of Bi NPs prepared at 60 ˚C was greater than that of samples prepared at 10 ˚C. Further, Bi NPs exhibited lower potency against E. coli than S. aureus in both samples.

Effect of laser shock peening on the surface integrity and fretting fatigue properties of high-strength titanium alloy TC21

High-strength titanium alloy TC21 is often used to make aircraft load-bearing components in the aviation field. However, due to vibration, load-bearing components often suffer from fretting fatigue (FF), which greatly reduces their actual service life. Nowadays, laser shock peening (LSP) is being recognized as an effective strengthening process for many materials. Therefore, in this study, the effectiveness of LSP on the strengthening of high-strength titanium alloy TC21 is studied, in terms of surface integrity and FF properties. TC21 fretting specimens and tests are designed. Before fretting tests, the specimens are processed by LSP with varying laser pulse energies, number of shocks and overlap rate, and their surface integrity and FF properties are analyzed. It is found that the greater the laser pulse energy and number of shocks, the higher the surface hardness and compressive residual stress, the more the grain refinement, the greater the improvement in FF life. Under 32J-50%-T1, the FF life is improved by 191.3% compared with BM. But the overlap rate has little effect on surface integrity and FF life. Meanwhile, there forms amorphous structures, which tended to be transformed into nanograins during fretting process. This transformation is helpful for prolonging FF life due to its action of energy absorption. This study reveals the strengthening mechanism of LSP on TC21 and its effect on the FF properties of TC21 specimens.

Ferroelectricity in Ultrathin HfO2-Based Films by Nanosecond Laser Annealing.

Nonvolatile memory devices based on ferroelectric HfxZr1-xO2 (HZO) show great promise for back-end integrable storage and for neuromorphic accelerators, but their adoption is held back by the inability to scale down the HZO thickness without violating the strict thermal restrictions of the Si CMOS back end of line. In this work, we overcome this challenge and demonstrate the use of nanosecond pulsed laser annealing (NLA) to locally crystallize areas of an ultrathin (3.6 nm) HZO film into the ferroelectric orthorhombic phase. Meanwhile, the heat induced by the pulsed laser is confined to the layers above the Si, allowing for back-end compatible integration. We use a combination of electrical characterization, nanofocused scanning X-ray diffraction (nano-XRD), and synchrotron X-ray photoelectron spectroscopy (SXPS) to gain a comprehensive view of the change in material and interface properties by systematically varying both laser energy and the number of laser pulses on the same sample. We find that NLA can provide remanent polarization up to 2Pr= 11.6 μC/cm2 in 3.6 nm HZO, albeit with a significant wake-up effect. The improved TiN/HZO interface observed by XPS explains why device endurance goes beyond 107 cycles, whereas an identical film processed by rapid thermal processing (RTP) breaks already after 106 cycles. All in all, NLA provides a promising approach to scale down the ferroelectric oxide thickness for emerging HZO ferroelectric devices, which is key for their integration in scaled process nodes.

Beyond symmetry: Investigating asymmetric melt pool evolution in multi-pulse laser surface melting

A numerical investigation is carried out to explore the intricacies of multi-pulse pulsed laser surface melting (pLSM) to understand its impact on surface evolution. A finite-element-based multi-phase model with temperature-dependent properties is employed to track the interface for multiple laser pulses. Examining various overlap spacings and conducting a comparative analysis of the number of pulses, the study focuses on the exclusive influence of overlapping in surface texture generation. Notably, the assumption of an initially flat surface eliminates the effects of the initial surface roughness to provide unique insights completely based on multi-pulse dynamics. While the first pulse on a flat initial surface resulted in a symmetric surface evolution, asymmetric melt pools were observed in the second pulse and subsequent pulses. The asymmetry results from non-uniform cooling and melt pool flows influenced by the surface evolved in the first pulse. The topography-driven surface tension from the first pulse made the trailing peak solidify slower than the leading peak. The asymmetry was significant for smaller overlaps between the two pulses and reduced as the overlap increased. Further, an increase in the number of laser pulses promotes the generation of identical asymmetric surface features. In conclusion, the study demonstrates the importance of the developed model in accurately predicting the surface evolution influenced by topography-driven surface tension and that single pulse axisymmetric models are insufficient.

Study on the Impact of Air Pressure on the Laser-Induced Breakdown Spectroscopy of Intumescent Fireproof Coatings

Intumescent fireproof coatings protect steel structures and cables by forming a thick, fire-resistant layer under high temperatures. These coatings can deteriorate over time, impacting their fire resistance. Current testing methods are largely lab-based, lacking in-service evaluation platforms. Laser-Induced Breakdown Spectroscopy (LIBS) is emerging as a promising in situ detection technology but is influenced by low air pressure in high-altitude areas. This study investigates how air pressure affects LIBS signals in intumescent coatings on galvanized steel. Using pressures between 35 and 101 kPa, a linear model was developed to correlate laser pulses to ablation depth for characterizing coating thickness. Results show that spectral intensity decreases with lower air pressure. However, a strong linear relationship persists between laser pulses and ablation depth, with a fitting accuracy above 0.9. The coating thickness is identified by the number of laser pulses required to detect the Zn spectral line from the underlying galvanized steel. As air pressure decreases, the ablation depth increases. The study effectively models and corrects for air pressure effects on LIBS data, enabling its application for field detection of fireproof coatings. This advancement enhances the reliability of LIBS technology in assessing the fire performance of these materials, providing a reference for their in situ evaluation and ensuring better fire safety standards for building steel structures and cables.

Threshold of stochastic self-focusing from the Poisson property of extreme-event statistics.

Statistics of self-focusing induced by a stochastic laser driver is shown to converge, in the large-sample-size limit, to a generalized Poisson distribution whose mean is given by the exponent of the respective extreme-value statistics. For a given ratio of the laser peak power to the self-focusing threshold Pcr, the mean number of self-focusing counts in a large sample of laser pulses is shown to depend on the number of pulses in the sample, N, and the signal-to-noise ratio of laser pulses, a. We derive a closed-form solution for the threshold of stochastic self-focusing, which, unlike its deterministic counterpart, Pcr, is a function of the sample size N and the signal-to-noise ratio a. The parameter Na = exp (a2/2) is shown to set a borderline between the deterministic and stochastic regimes of self-focusing. When the number of laser pulses in a sample becomes comparable to Na, self-focusing can no longer be viewed as deterministic even for high signal-to-noise laser beams.

INVESTIGATION OF X-RAY EMISSION FROM LASER PRODUCED ALUMINIUM ANTIMONIDE PLASMA

Lasers are integral to numerous applications in our daily lives, with one of their notable uses being the ablation of materials to generate plasma, which in turn produces X-rays with a variety of applications. This study investigates the generation of hard X-rays from Aluminum Antimonide (AlSb) plasma, induced by a Q-switched Nd: YAG laser operating at 1064[Formula: see text]nm with a pulse duration of 9–14[Formula: see text]ns and a peak power of 1.1[Formula: see text]MW. The AlSb target was selected due to its unique electronic structure and high atomic number, which are advantageous for efficient X-ray generation. At a tight focus, the laser produced a spot size of 11.8 micrometers, achieving an intensity of 1012 W/cm[Formula: see text], to study the transmission of hard X-rays both in a vacuum environment with a pressure of 10[Formula: see text] torr and in air at atmospheric pressure. A Photo Multiplier Tube (PMT) was employed to detect the transmitted hard X-rays, which were filtered using a 10 [Formula: see text]m-thick Al filter. The fundamental mechanisms behind the emission of hard X-rays from laser-induced AlSb plasma were explored. Plasma plume expansion and the energy of the emitted radiation were found to depend on the number of laser pulses and the ambient pressure. The intensity of the plasma plume was observed to be inversely proportional to the ambient pressure and directly proportional to the number of laser pulses fired. Plasma confinement under high pressures was also examined. Time-resolved studies of the hard X-ray emission contributed to the analysis. The relationship between different laser shots and the current, voltage, and energy of the hard X-rays, as well as their inverse proportionality to ambient pressure, was quantified. At an ambient pressure of 10[Formula: see text] torr, the dynamics of the AlSb plasma plume were observed. The surface morphology of the laser-irradiated AlSb target was also analyzed, revealing unique properties pertinent to X-ray emission.

Laser induced breakdown spectroscopy for composition monitoring of graded Al[sbnd]Cu alloy surface

Laser-induced breakdown spectroscopy (LIBS) is a powerful method for non-invasive elemental composition monitoring which can be applied for processing graded metal alloys, provided that challenges with reliable and rapid spectral data processing are overcome to enable composition analysis in real-time. In this study, we describe an integrated experimental-computational methodology for analyzing LIBS spectra data obtained from graded composition metal alloy surfaces with a mean rate of composition analysis up to 15.7 Hz. The accuracy and speed of this method was assessed via analysis of a graded AlCu film prepared by magnetron sputtering representing a gradient alloy processed by additive manufacturing. Using a pulsed femtosecond laser and gated sCMOS detector, a series of LIBS measurements were taken across the composition gradient of an AlCu sputtered alloy. Energy Dispersive Spectroscopy (EDS) was used both to calibrate composition measurements and quantify the error of the LIBS-based rapid analysis method demonstrated in this paper, which yielded a mean percent error relative to the EDS data in the composition measurement along the gradient as low as 1.4 % when optimized for the cumulative number of probe laser pulses on a single measurement spot. The femtosecond probe pulse method described in this paper allows for the alloy composition to be accurately measured in hundredths of a second, potentially allowing for real-time composition monitoring in gradient alloy processing, including thin film sputtering, additive manufacturing, and other rapid processing technologies for graded metal alloys.

Femtosecond Bessel laser beam induced concentric rings on SiC for circular symmetry wide-viewing angle structural color

The laser-induced structural coloring technique holds significant potential for various applications due to its precision, controllability, and versatility across different materials. However, laser-induced structural colors face the problems of durability, homogeneity and indistinguishability, which are not conducive to their application as large-scale identifiable markers. In this paper, an innovative approach has been developed to achieve a circular-symmetric structural color display on durable SiC surfaces by fabricating periodic concentric ring structure arrays using the sidelobe light field of a femtosecond zero-order Bessel beam. The research involved a systematic study of the effects of laser power and pulse number on SiC, along with a detailed analysis of the micro-nanostructures evolving on the SiC surface after laser scanning. Additionally, an examination of the characteristics of circular-symmetric structural color displays and their wide viewing angles in periodic circular structures was conducted. Finally, a comparison was made between the structural color display effects of a concentric ring structure generated by a single pulse and the Laser-Induced Periodic Surface Structures (LIPSS) generated by three pulses. This comparison underscores the potential application of alternating between the high saturation color of the concentric ring structure and the low saturation dark light of the LIPSS for anti-counterfeit coding purposes. The findings of this research present promising opportunities for low-cost mass manufacturing in anti-counterfeit labeling and the advanced processing of photonic devices using SiC.

Controllable Preparation of Fused Silica Micro Lens Array through Femtosecond Laser Penetration-Induced Modification Assisted Wet Etching.

As an integrable micro-optical device, micro lens arrays (MLAs) have significant applications in modern optical imaging, new energy technology, and advanced displays. In order to reduce the impact of laser modification on wet etching, we propose a technique of femtosecond laser penetration-induced modification-assisted wet etching (FLIPM-WE), which avoids the influence of previous modification layers on subsequent laser pulses and effectively improves the controllability of lens array preparation. We conducted a detailed study on the effects of the laser single pulse energy, pulse number, and hydrofluoric acid etching duration on the morphology of micro lenses and obtained the optimal process parameters. Ultimately, two types of fused silica micro lens arrays with different focal lengths but the same numerical aperture (NA = 0.458) were fabricated using the FLPIM-WE technology. Both arrays exhibited excellent geometric consistency and surface quality (Ra~30 nm). Moreover, they achieved clear imaging at various magnifications with an adjustment range of 1.3×~3.0×. This provides potential technical support for special micro-optical systems.

The role of thickness on the structural and luminescence properties of Y2O3:Ho3+, Yb3+ upconversion films

The structural, surface, and upconversion (UC) luminescence properties of Y2O3:Ho3+,Yb3+ films grown by pulsed laser deposition, for different numbers of laser pulses, were studied. The crystallinity, surface, and UC luminescence properties of the thin films were found to be highly dependent on the number of laser pulses. The X-ray powder diffraction analysis revealed that Y2O3:Ho3+,Yb3+ films were formed in a cubic structure phase with an Ia 3¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\overline{3 }$$\\end{document} space group. The thicknesses of the films were estimated by using cross-sectional scanning electron microscopy, depth profiles using X-ray photoelectron spectroscopy (XPS), and the Swanepoel method. The high-resolution XPS was used to determine the chemical composition and oxidation states of the prepared films. The UC emissions were observed at 538, 550, 666, and 756 nm, assigned to the 5F4 → 5I8, 5S2 → 5I8, 5F5 → 5I8, and 5S2 → 5I7 transitions of the Ho3+ ions. The power dependence measurements confirmed the involvement of a two-photon process in the UC process. The color purity estimated from the Commission International de I’Eclairage coordinates confirmed strong green UC emission. The results suggested that the Y2O3:Ho3+,Yb3+ UC transparent films are good candidates for various applications, including solar cell applications.

Exploring the viability of combined laser-induced breakdown spectroscopy and Raman spectroscopy for stratigraphic analysis of murals containing isomeric pigments: a case study on realgar and orpiment

A novel combined measurements techniques has been designed in this work, enabling the acquisition of laser-induced breakdown spectroscopy (LIBS) and Raman spectral signals at the same point on a sample. The application of this combined technique to the analysis of multi-layered mock-up blocks painted with orpiment and realgar pigments has yielded significant insights. By correlating variations in the emission line intensity of characteristic elements within the LIBS spectra with depth-specific Raman spectra, the number of laser pulses that penetrated the pigment layers has been accurately determined, thereby establishing a method to measure layer thickness. Finally, the technique wasto analysis the actual mural fragment from Mogao Cave 196, determining the types of pigment and the thickness of the pigment layers.Graphical

Atom Probe Tomography of the LiFePO4-Electrolyte Interface Enabled by Thin Film Electrodes

Atom probe tomography (APT) can yield three-dimensional tomographic images at atomic-scale resolution and low-AMU elements such as Li are readily observed, making it a powerful tool for exploring battery materials interfaces. However, it is difficult to prepare APT specimen tips containing the interface of interest starting with typical particle-based battery electrodes. Here we demonstrate a methodology for reliable APT imaging of battery interfaces in which a thin film electrode geometry is used to provide well-controlled planar interfaces that are ideal for APT sample preparation and imaging. LiFePO4 (LFP) thin film electrodes, synthesized using pulsed laser deposition (PLD), were studied as an example system, with standard Li-salt electrolytes. For the results to be applicable to conventional particulate electrodes, it is important to obtain representative thin film structure and electrochemical characteristics. Thus, the effects of PLD conditions including substrate temperature, substrate crystallinity, target composition, and deposition time (number of laser pulses) on the thin film’s crystallographic texture, morphology, and electrochemical performance were studied. Optimized LFP film showed good crystallinity with low-C-rate capacity of ∼90 mAh g−1. Initial APT three-dimensional imaging of the LFP/electrolyte interface shows an ∼10 nm cathode-electrolyte interphase layer that is enriched in F and Li.

Laser-Induced Breakdown Spectroscopy Analysis of Sheet Molding Compound Materials

Sheet Molding Compound (SMC) materials are extensively utilized as high-voltage insulation materials in electrical equipment. SMC materials are prone to aging after long-term operation. Conducting non-destructive testing to assess their electrical and physicochemical properties is crucial for the safe operation of electrical equipment. This study identifies the optimal equipment parameters for testing SMC materials using Laser-Induced Breakdown Spectroscopy (LIBS) technology through experimental investigation and also explores the ablation characteristics of SMC under various laser parameters. The results indicate a significant positive correlation between the ablation depth and laser pulse number, while there is no correlation with single laser pulse energy. However, the ablation area demonstrates a strong positive correlation with both single laser pulse energy and laser pulse number. Additionally, LIBS spectral analysis provides elemental results comparable to Energy Dispersive Spectroscopy (EDS), facilitating the examination of variations in Na, Ti, Fe, Mg, Ca, and C elemental contents with depth. Moreover, an enhanced iterative Boltzmann plot method is suggested for calculating the plasma temperature using 21 Fe I spectral lines and the electron density using the Fe II 422.608 nm line. The variations of these plasma parameters with laser pulse number are documented, and the results show consistent trends, confirming that the laser-induced SMC plasma adheres to local thermodynamic equilibrium.

Ex-vivo parametric study of laser ablation-based drilling of cortical bone.

Frequently orthopedic surgeries require mechanical drilling processes especially for inserted biodegradable screws or removing small bone lesions. However mechanical drilling techniques induce large number of forces as well as have substantially lower material removal rates resulting in prolong healing times. This study focuses on analyzing the impact of quasi-continuous laser drilling on the bone's surface as well as optimizing the drilling conditions to achieve high material removal rates. An ex-vivo study was conducted on the cortical region of desiccated bovine bone. The laser-based drilling on the bovine bine specimens was conducted in an argon atmosphere using a number of laser pulses ranging from 100 to 15,000. The morphology of the resulting laser drilled cavities was characterized using Energy dispersive Spectroscopy (EDS) and the width and depth of the drills were measured using a laser based Profilometer. Data from the profilometer was then used to calculate material removal rates. At last, the material removal rates and laser processing parameters were used to develop a statistical model based on Design of Experiments (DOE) approach to predict the optimal laser drilling parameters. The main outcome of the study based on the laser drilled cavities was that as the number of laser pulses increases, the depth and diameter of the cavities progressively increase. However, the material removal rates revealed a decrease in value at a point between 4000 and 6000 laser pulses. Therefore, based on the sequential sum of square method, a polynomial curve to the 6th power was fit to the experimental data. The predicted equation of the curve had a p-value of 0.0010 indicating statistical significance and predicted the maximum material removal rate to be 32.10 mm3/s with 95%CI [28.3,35.9] which was associated with the optimum number of laser pulses of 4820. Whereas the experimental verification of bone drilling with 4820 laser pulses yielded a material removal rate of 33.37 mm3/s. Therefore, this study found that the carbonized layer formed due to laser processing had a decreased carbon content and helped in increasing the material removal rate. Then using the experimental data, a polymetric equation to the sixth power was developed which predicted the optimized material removal rate to occur at 4820 pulses.

Spray mist-assisted drilling of through silicon vias (TSV) using nanosecond laser: Influence of CNT nanofluid

Through Silicon Vias (TSV) are crucial in semiconductor technology for vertically connecting multiple stacks in 3D packaging. High aspect ratio, smooth and slightly tapered TSVs enhance layout efficiency and void-free filling. Being contact-less and dry-etching process, laser machining is a promising technique to fabricate TSVs. A percussion laser drilling approach was used to fabricate TSVs on a 500 μm thick silicon wafer with a 1064 nm ns laser. Four environments such as air, compressed air jet, water mist, carbon nanotube (CNT) fluid mist were employed to assess laser machining effects on TSV performance in terms of entrance and exit diameters, recast layer, side wall damage, and taper angle. Optimized process parameters (laser pulse energy and pulse number) were derived from an ANN prediction model. Laser drilling under CNT mist produced relatively circular (entrance diameter), straight, and clean TSVs. Reduced debris redeposition was observed under air jet, water mist, and CNT mist compared to air. Minimal sidewall damage occurred under water mist and CNT mist as compared to those machined in air and air jet. CNT mist yielded TSVs with less recast layer (∼7 μm), taper angle (∼1.05 deg.), and heat affected zone (HAZ) thickness (∼50 μm). Enhanced machining quality may be attributed to increased thermal conductivity of CNT nanofluid and pressurized mist flow rate, improving cooling and debris removal. Furthermore, a detailed investigation of TSV using SEM was performed and the findings were compared to those of other research groups.

Characteristics of aluminium nitride thin film prepared by pulse laser deposition with varying laser pulses

In this work, the studies of Aluminium Nitride (AlN) thin film deposited on silicon (Si) (111) substrate using the pulsed laser deposition (PLD) method, specifically under different number of laser pulses, were performed. From the electron micrographs, the samples exhibited a densely packed granular morphology. The film thickness, particle size, and surface roughness were found to be increasing along with number of laser pulses. X-ray diffraction analysis revealed all AlN samples to have hexagonal wurtzite structure. Additionally, the calculated lattice constants suggest AlN experiences inward biaxial stress during growth. This was in agreement with the Raman results, aside from substantiating the presence of AlN with (100) and (101) plane to be grown. Room temperature photoluminescence (PL) measurements showed band-edge emission was attributed to AlN along with some defect-related bands. Additionally, the band-edge emission shifted to higher photon energy, i.e. 5.49–5.89 eV with increasing laser pulses. Such observations were consistent with that obtained from UV–Vis spectroscopy.

Comparative Numerical Analysis of Keyhole Shape and Penetration Depth in Laser Spot Welding of Aluminum with Power Wave Modulation

Keyhole mode laser welding is a valuable technique for welding thick materials in industrial applications. However, its susceptibility to fluctuations and instabilities poses challenges, leading to defects that compromise weld quality. Observing the keyhole during laser welding is challenging due to bright process radiation, and existing observation methods are complex and expensive. This paper alternatively presents a novel numerical modeling approach for laser spot welding of aluminum through a modified mixture theory, a modified level-set (LS) method, and a thermal enthalpy porosity technique. The effects of laser parameters on keyhole penetration depth are investigated, with a focus on laser power, spot radius, frequency, and pulse wave modulation in pulsed wave (PW) versus continuous wave (CW) laser welding. PW laser welding involves the careful modulation of power waves, specifically adjusting the pulse width, pulse number, and pulse shapes. Results indicate a greater than 80 percent increase in the keyhole penetration depth with higher laser power, pulse width, and pulse number, as well as decreased spot radius. Keyhole instabilities are also more pronounced with higher pulse width/numbers and frequencies. Notably, the rectangular pulse shape demonstrates substantially deeper penetration compared to CW welding and other pulse shapes. This study enhances understanding of weld pool dynamics and provides insights into optimizing laser welding parameters to mitigate defects and improve weld quality.