Increasing Laser Energy Research Articles

Unraveling microstructure and mechanical response of an additively manufactured refractory TiVHfNbMo high-entropy alloy

Refractory high-entropy alloys (RHEAs) have attracted considerable interest due to their elevated melting points and exceptional softening resistance. Nevertheless, the ambient-temperature brittleness and inadequate high-temperature oxidation resistance commonly restrict the processability of RHEAs. Direct energy deposition (DED) additive manufacturing technology is ideal for fabricating refractory alloys due to design flexibility and oxygen-free environment. In this work, a novel Ti41V27Hf13Nb13Mo6 RHEA was successfully manufactured by DED, and a comprehensive investigation was conducted to explore the microstructure evolution and mechanical response during tension. The as-deposited RHEAs exhibit a grain-size graded microstructure with a body-centred-cubic (BCC) matrix and precipitates. Increasing laser energy density suppressed the grain boundary precipitation, effectively enhancing the ambient-temperature tensile ductility to ∼11.3%. The optimized specimens achieved an unprecedented yield strength of ∼1.2 GPa among the DEDed RHEAs, which can be attributed to a significant solid solution strengthening from the volume misfit of 5.03%. We revealed that dislocation interactions maintained the working hardening capacity. Moreover, in-situ characterization indicated that slip transfer, grain rotation, and kinking accommodated the plastic deformation. Crack nucleation was caused by slip inhibition at grain boundaries and dislocation pile-ups at intragranular precipitates. The kink band formation relieved stress concentration induced by intragranular precipitates and promoted a ductile fracture. These exceptional outcomes provide opportunities for additive manufacturing RHEAs and greatly advance understanding of their strengthening and deformation mechanisms.

Microstructural evolution, mechanical properties and corrosion mechanisms of additively manufactured biodegradable Zn-Cu alloys

Additively manufactured (AM) biodegradable zinc (Zn) alloys constitute an important branch of orthopedic implants because of their moderate degradation properties and bone-mimicking mechanical properties. In this paper, the microstructural evolution and corrosion mechanisms of zinc-copper (Zn-Cu) alloys prepared by the laser-powder-bed-fusion (L-PBF) additive manufacturing method were investigated. Alloying with Cu significantly increases the ultimate tensile strength (UTS) of unalloyed Zn, but the UTS and ductility of unalloyed Zn and Zn-2Cu decrease with increasing laser energy density. Unalloyed Zn has a dendritic microstructure, while Zn-2Cu alloy has a peritectic microstructure. The formation of round peritectic grains is due to the low-temperature gradient of unalloyed Zn during the AM. The Zn-2Cu samples exhibited higher corrosion rates, addressing the problem of slow degradation of unalloyed Zn. The grain size distribution influences the corrosion behavior of the material. It enhances the corrosion rates of materials with fine grains in a non-passivating environment. However, the 100% extracts of Zn-2Cu samples exhibited greater values of cellular activity compared to unalloyed Zn samples, thus confirming their better cytocompatibility. This work demonstrates the great potential to design and modulate biodegradable Zn alloys to fulfill clinical needs by using AM technology.

Preliminary Investigation of Thermoelectric Electromotive Force Oscillation of NiCr/NiSi Thin Film Thermocouple in Dynamic Calibration.

In order to reveal the dynamic response characteristic of thin film thermocouples (TFTCs), the nichrome/nisil (NiCr/NiSi) TFTCs are prepared onto the glass substrate. With short pulse infrared laser system, NiCr/NiSi TFTCs are dynamically calibrated. The thermoelectric electromotive force (TEF) curves of NiCr/NiSi TFTCs are recorded by the memory hicorder system, which could reflect TEF signals with resolution ratio in nanosecond and microvolt, simultaneously. With increasing laser energy from 15.49 to 29.59 mJ, TEF curves display more and more violent oscillation, even negative value. The results show that the bounce of thermal energy happens between two interfaces of TFTCs because the thermal conductivity of glass and air is significantly lower than that of NiSi/NiCr TFTCs. The bounce of thermal energy results in the obvious decrease of nNiCr and nNiSi, as well as oscillation of TEF. For laser energy in 29.59 mJ, the bounce of thermal energy in NiCr film could result in nNiCr < nNiSi. Then, TEF value appears abnormal negative value. Based on the results, the complex thermal energy transport process in TFTCs dynamic calibration is revealed, which results in the oscillation of thermal energy and TEF signal.

Effect of laser energy on temporal evolution of self-absorption at different air pressures

The self-absorption effect is one of the key factors influencing the accuracy of quantitative analysis. Laser energy is the key influencing factor of laser-induced breakdown spectroscopy (LIBS), and the mechanism of its influence on temporal evolution of self-absorption under different air pressures is still not fully understood due to complex physical processes. In this study, the temporally resolved spectra of Cu I 521.82 nm were acquired from the direction of laser incidence and the influence of laser energy on the temporal evolution of self-absorption in a low-vacuum (at pressures of 105, 104 and 103Pa) and high-vacuum (at pressures of 10, 10−1 and 10−3Pa) environment was studied. The experimental results indicate that the self-absorption effect of spectral line Cu I 521.82 nm is enhanced with an increase in delay time and laser energy in both high-vacuum and low-vacuum environments in this study. This is because increasing the delay time and laser energy leads to an increase in plasma column density. An intriguing phenomenon observed in this experiment is that at a pressure of 105Pa, the self-absorption of Cu I 521.82 nm initially increases but eventually weakens with laser energy, while at air pressures of 104Pa and 103Pa the self-absorption monotonically weakens with increasing laser energy during the measurement. This is because temporal evolution of plasma at 104Pa and 103Pa is significantly faster than that at 105Pa, and an increase in laser energy can delay the enhancement of self-absorption, the self-absorption has rapidly evolved to decrease with laser energy during spectral measurement at air pressure of 104 Pa and 103 Pa. This work is helpful in understanding the influence of air pressure and laser energy on the self-absorption effect of spectral lines and optimizing experimental parameters, and provides a reference for LIBS application.

Effect of laser cavitation peening on surface integrity and electrochemical corrosion behavior of magnesium alloy

A novel method of laser cavitation peening (LCP) was employed to process the AZ31B magnesium (Mg) alloy. The processes of bubble evolution and LCP impact were investigated. The influences of LCP on the surface integrity (surface morphology and roughness, microhardness, residual stress, phase) and electrochemical corrosion behavior of AZ31B Mg alloy under various processing parameters (laser energy and defocusing amount) were systemically investigated. The results show that the laser breakdown extent, bubble radius, pulsation period, and bubble energy increase with the increase of laser energy. The maximum radius of the cavitation bubble decreases significantly as the defocusing amount increases from 0 mm to 2 mm. LCP enhances the microhardness and introduces the compressive residual stress into the surface layer of the AZ31B, but it also increases the surface roughness. The surface morphology of LCP processed AZ31B has significant differences under various processing parameters, and the microhardness and residual stress increase as increasing the laser energy. LCP improves the anti-corrosion of AZ31B effectively except for the condition of 200 mJ laser energy. The best defocusing amount for enhancing the surface integrity and electrochemical performance of AZ31B by LCP processing is 1 mm, and the higher laser energy has the better corrosion resistance.

Role of power on physiochemical properties of Mo- and Ni-based nanoparticles manufactured by laser ablation

In this study, the influence of the laser energy on Molybdenum (Mo) and Nickel (Ni) based nanoparticles (NPs) produced by laser ablation is presented. The nanoparticles' physicochemical properties were studied for laser energy values from 70 to 300 mJ for Mo and from 100 to 250 mJ for Ni. X-ray Diffraction, Atomic Force Microscopy, Dynamic Light Scattering, Atomic Absorption, and UV–Vis Spectroscopy allowed for studying the crystalline structure, morphology, composition, and optical properties. Both samples Mo and Ni at low laser energies produce amorphous nanoparticles with sizes of 30 and 15 nm, respectively. When the laser energy increases, the crystalline structure, size, concentration, and optical properties of the molybdenum and nickel nanoparticles change. However, the shape of the nanoparticles (quasi-spherical) is independent of the laser energy. In Mo, NPs showed a monocrystalline MoO3 phase at intermediate laser energy. At high values of laser energy, Mo is the most stable structure. In Ni, NPs showed a polycrystalline NiO phase at medium laser energy. At high values of laser energy, a mixture of NiO and Ni is the most stable structure. The particle size remains constant for intermediate and high laser energy values. The main difference between the hydrodynamic diameter and the particle size was 7 nm. UV–vis spectra of Mo nanoparticles showed the formation of two compounds: (MoO4)2- and H2MoO4. UV–vis spectra of Ni nanoparticles showed that the absorbance decreased continuously above 200 nm, except for the sample prepared at 150 mJ. As the laser energy increases, the concentration of NPs increases in both cases. We concluded that the Ni sample at 150 mJ shows potential stability compared to the others due to the electrical charging of the material during the ablation process. As the most important result found in this research, it can be considered that the laser energy affects the structural, morphological, and compositional properties of Ni and Mo-based nanoparticles. Nevertheless, as expected, the most significant influence was observed in the nanoparticle concentration. The novelty of the work consists of the laser energy on the band gap and, precisely, the results for Ni-based nanoparticles. In this case, it was impossible to measure this parameter for almost all samples, possibly due to the magnetic influences, since the unoccupied d states atoms, such as Ni, are responsible for the ferromagnetism or high paramagnetism of the transition elements. There is a direct connection between the magnetic properties and the electrical conductivity. On the other hand, in the case of Mo-based nanoparticles, the influence of laser energy on the bandgap is almost negligible.

Evolution of point defects in pulsed-laser-melted Ge1-x Sn x probed by positron annihilation lifetime spectroscopy

Direct-band-gap Germanium-Tin alloys (Ge1-x Sn x ) with high carrier mobilities are promising materials for nano- and optoelectronics. The concentration of open volume defects in the alloy, such as Sn and Ge vacancies, influences the final device performance. In this article, we present an evaluation of the point defects in molecular-beam-epitaxy grown Ge1-x Sn x films treated by post-growth nanosecond-range pulsed laser melting (PLM). Doppler broadening – variable energy positron annihilation spectroscopy and variable energy positron annihilation lifetime spectroscopy are used to investigate the defect nanostructure in the Ge1-x Sn x films exposed to increasing laser energy density. The experimental results, supported with ATomic SUPerposition calculations, evidence that after PLM, the average size of the open volume defects increases, which represents a raise in concentration of vacancy agglomerations, but the overall defect density is reduced as a function of the PLM fluence. At the same time, the positron annihilation spectroscopy analysis provides information about dislocations and Ge vacancies decorated by Sn atoms. Moreover, it is shown that the PLM reduces the strain in the layer, while dislocations are responsible for trapping of Sn and formation of small Sn-rich-clusters.

Chemical etching enhanced nanosecond pulsed laser micromachining: An experimental and numerical investigation

Nanosecond pulsed laser micromachining (PLM) under liquid confinement is a highly precise, flexible, efficient, and non-contact manufacturing process being used in widespread applications. The process efficiency of the PLM as determined by the laser ablation rate, however, often quickly reaches saturation with the increase of laser energy. This is ascribed to the screening effect of laser-induced plasma that absorbs part of incident energy. In this study, a chemical etching enhanced PLM (CE-PLM) is developed to tackle this challenge. By replacing water (H2O) with an environmentally friendly and active liquid confinement - hydrogen peroxide (H2O2), single-shot laser ablation experiments were firstly performed on different metallic materials to evaluate the considerably enhanced ablation rate. Then, the beneficial effects of H2O2 on PLM applications including micro-drilling and micro-grooving were investigated. The enhanced ablation rate and PLM efficiency were attributed to the synergistic effect of laser ablation and ultrafast chemical etching. Moreover, a physics-based model was developed to elucidate the process mechanism, with focus on revealing the contribution of chemical etching to the material removal during CE-PLM as affected by laser processing parameters. The findings of this study will contribute to enhancing the efficiency and capability of PLM techniques towards broader industrial applications.

Evaluation of antibacterial effect of a cationic porphyrin derivative on Pseudomonas aeruginosa in photodynamic therapy

BackgroundPseudomonas aeruginosa is a gram-negative bacterium without spores, and it is one of the pathogens that easily cause secondary infectious diseases when human immune function is low. The purpose of this study is to explore the inhibitory effect of photodynamic antibacterial chemotherapy-induced by cationic porphyrin derivative on clinical P. aeruginosa and its mechanism. MethodsThe uptake of photosensitizer by P. aeruginosa and L929 cells was measured by an ultraviolet spectrophotometer. Effect of laser energy density on the bacterial activity of P. aeruginosa and post antibiotic effect were measured by bacterial suspension and tenfold dilution method. Flow cytometry and scanning electron microscopy were used to observe the activity and morphological changes of P. aeruginosa after PACT treatment. ResultsThe uptake of Tetra-ATPP-Lys-by P. aeruginosa and L929 was shown as concentration-dependent and time-dependent. However the uptake of L929 cell had a clear difference with P. aeruginosa at the same time and concentration intervals(P < 0.05).The increasing laser energy density had a high inactivation effect of on P. aeruginosa at the same Tetra-ATPP-Lys-concentration(P < 0.05). Post-antibiotic effect of Tetra-ATPP-Lys -PACT was dose-dependent(P < 0.05). Bacterial viability which evaluated by the flow cytometry method demonstrated that the proportion of viable bacteria is decreased with the photosensitizer dose-dependent. The morphology and microstructure of P. aeruginosa after Tetra-ATPP-Lys -PACT was demonstrated by a scanning electron microscope(SEM). After PACT, the morphology of P. aeruginosa was rod-shaped, the outer membrane surface was rough, and the bacteria were dry flat, sunken, shrunk and deformed. ConclusionsCationic porphyrin photosensitizer had a great damage effect on P. aeruginosa under the PACT, which can effectively destroy the microstructure of bacteria and lead to bacterial inactivation and death.

Rapid photo-bleaching gamma irradiated Yb-doped optical fibers by high-energy ns pulsed laser

A rapid and efficient photo-bleaching process was demonstrated with a high-energy nanosecond pulse to recover existing and/or revealed color centers on 10 kGy Gamma-irradiated Yb-doped optical fiber. Multi-mJ pulsed laser based on an optical parametric amplifier system operating at wavelengths of 532 nm, 680 nm and 793 nm was used. The photo-bleaching performance is investigated as a function of the wavelength and energy of the pulsed light source. It was observed that the photo-bleaching level of the Yb-doped optical fiber increased when the exposure time of the pulsed laser light and the photon energy was increased. The maximum PB occurred in the pulsed laser of 532 nm wavelength in the optical fiber. Also, a drastically increase in the PB was observed due to the increasing laser energy at the wavelength of 532 nm and 680 nm pulsed laser. The results show that the recovery levels of color centers in the Yb-doped optical fibers could be reached up to 96 % in a shorter time (h) by using the pulsed laser compared to that of the studies using continuous laser.

Трансцилиарное дренирование задней камеры в лечении закрытоугольной глаукомы

The review presents the main existing transcilliary drainage of posterior chamber (TDPC) methods used nowadays. We tried to analyze existing key articles and patents issued for methods of treating glaucoma. Based on the literature data, we found that TDPC is a safe and effective method for the treatment of angleclosure glaucoma, and application of various parameters of laser energy and drainage process increase efficiency of this procedure. At the same time, the rapid progression of the glaucoma process requires constant improvement of modern TDPC techniques. Key words: angle-closure glaucoma, transciliary drainage of the posterior chamber

Effects of low-level laser on the expression of interleukin-6, tumor necrosis factor‑α, osteoprotegerin, and receptor activator of nuclear factor-κB ligand in human periodontal ligament cells.

This study aims to determine the effects of low-level laser (LLL) on the expression of interleukin-6 (IL-6), tumor necrosis factor (TNF)-α, osteoprotegerin (OPG), and receptor activator of nuclear factor-κB ligand (RANKL) in human periodontal ligament cells (HPDLCs) stimulated by high glucose; and identify the molecular mechanism of LLL therapy in the regulation of periodontal inflammation and bone remodeling during orthodontic treatment in diabetic patients. HPDLCs were cultured in vitro to simulate orthodontic after loading and irradiated with LLL therapy. The cultured cells were randomly divided into four groups: low glucose Dulbecco's modification of Eagle's medium (DMEM)+stress stimulation (group A), high glucose DMEM+stress stimulation (group B), hypoglycemic DMEM+LLL therapy+stress stimulation (group C), and hyperglycemic DMEM+LLL therapy+stress stimulation (group D). Groups C and D were further divided into C1 and D1 (energy density: 3.75 J/cm2) and C2 and D2 (energy density: 5.625 J/cm2). Cells in groups A, B, C, and D were irradiated by LLL before irradiation. At 0, 12, 24, 48, and 72 h, the supernatants of the cell cultures were extracted at regular intervals, and the protein expression levels of IL-6, TNF-α, OPG, and RANKL were detected by enzyme-linked immunosorbent assay. 1) The levels of IL-6 and TNF-α secreted by HPDLCs increased gradually with time under static pressure stimulation. After 12 h, the levels of IL-6 and TNF-α secreted by HPDLCs in group A were significantly higher than those in groups B, C1, and C2 (P<0.05), which in group B were significantly higher than those in groups D1, and D2 (P<0.01). 2) The OPG protein concentration showed an upward trend before 24 h and a downward trend thereafter. The RANKL protein concentration increased, whereas the OPG/RANKL ratio decreased with time. Significant differen-ces in OPG, RANKL, and OPG/RANKL ratio were found among group A and groups B, C1, C2 as well as group B and groups D1, D2 (P<0.05). 1) In the high glucose+stress stimulation environment, the concentrations of IL-6 and TNF-α secreted by HPDLCs increased with time, the expression of OPG decreased, the expression of RANKL increased, and the ratio of OPG/RANKL decreased. As such, high glucose environment can promote bone resorption. After LLL therapy, the levels of IL-6 and TNF-α decreased, indicating that LLL therapy could antagonize the increase in the levels of inflammatory factors induced by high glucose environment and upregulate the expression of OPG in human HPDLCs, downregulation of RANKL expression in HPDLCs resulted in the upregulation of the ratio of OPG/RANKL and reversed the imbalance of bone metabolism induced by high glucose levels. 2) The decrease in inflammatory factors and the regulation of bone metabolism in HPDLCs were enhanced with increasing laser energy density within 3.75-5.625 J/cm2. Hence, the ability of LLL therapy to modulate bone remodeling increases with increasing dose.

Linear-to-circular polarization conversion with full-silica meta-optics to reduce nonlinear effects in high-energy lasers

High-energy lasers have benefited from intense efforts to bring light-matter interactions to new standards and to achieve laser fusion ignition. One of the main issues to further increasing laser energy is the resistance of optical materials to high laser fluences, in particular at the final stage of the laser beamline where nonlinear Kerr effects can occur in optical materials and provoke laser filamentation. One promising way to mitigate this process is to reduce the nonlinear susceptibility of the material by switching the polarization from a linear to a circular state. Here, we report a significant reduction in the laser filamentation effect on glass by using a full-silica metamaterial waveplateable to switch the linear-to-circular polarization of high fluence laser beams. This result is achieved through the use of a large size full-silica meta-optics exhibiting nominal polarization conversion associated with an excellent transmission efficiency and wavefront quality, as well as a high laser damage resistance.

PEG–MoS2 Nanocomposite by Laser Ablation: Laser Energy Effects on Structural and Optical Properties for Photodiode Applications

In this study, we fabricated a composite of polyethylene glycol (PEG) with molybdenum disulfide (MoS[Formula: see text] using the laser ablation method for the first time, with different energy levels of 100, 300 and 500[Formula: see text]mJ. The structural, optical and thermal properties of the composite were investigated using various characterization techniques. The UV–Vis spectra showed a redshift in the absorption edge with the increase in laser energy. The FTIR spectra indicated the presence of functional groups in both PEG and MoS2, and the characteristic peaks of both components were observed. The refractive index of the composite was found to decrease with an increase in laser energy. TEM images revealed the presence of rod-like and spherical particles with different sizes. The energy gap of the composite was also found to decrease with an increase in laser energy. The high absorption of the composite in the near-visible and visible regions allowed the photodiode to detect light with high sensitivity and accuracy. It is showing that the forward bias current of ([Formula: see text][Formula: see text]Amp) is still relatively low and further optimization of the photodiode design and materials could lead to even higher current values and improved performance. These results suggest that the laser energy has a significant effect on the properties of the PEG–MoS2 composite. The obtained results demonstrate that the PEG–MoS2 composite has potential applications in various fields, including solar cells and drug delivery systems.

Laser shock dynamic compaction of aluminum–copper (Al–Cu) composite metal powder

Laser impact dynamic compaction experiments and 2D multi-particle finite element method (MPFEM) simulations were carried out on aluminum–copper (Al–Cu) binary-based composite powders. Al–Cu compacts with densities of about 95% were successfully prepared at the maximum laser energy of 1.8 J. Research trends indicate that higher power lasers could nearly achieve the theoretical densities. Analysis of the influence laws of laser energy and copper powder mass fraction on the densities of Al–Cu compacts was carried out, and the effects of microstructure and microhardness of Al–Cu compacts on their mechanical properties were investigated, as well as the stresses and velocities in the dynamic compaction process of Al–Cu composite powders were analyzed. The results showed that the relative densities of composite powder compacts of Al-5 wt%Cu gradually exceeded those of Al-10 wt%Cu and Al-15 wt%Cu with the increase of laser energy. In laser impact dynamic compaction the mechanism of inter-particle joining was solid-state press-welding, and the increase in the hardness of the Al–Cu compacts could be attributed to the inherent hardness of the hard particles. The upper particles have a localized maximum velocity of more than 300 m/s, which met the explosion welding velocity, thus localized cold welding occurred and contributed to the inter-particle connection.

Influence of annealing time on structural, morphological properties of TiO2 Films prepared by pulsed laser deposition

TiO2 films were fabricated by pulsed laser deposition (PLD) on glass substrates. XRD and AFM were used to study structural and surface morphology. XRD chart revelled steady increments of the intensity of the main peak of TiO2 of the films with the increase of laser power. The piratical sizes of the film were 43.10nm. The Atomic Force Microscope images show that surface roughness of the films was improved with the increase of laser energy. These results propose the possibility to enhance the structural properties of the TiO2 films and also it is possible to obtain high quality TiO2 film by variation of power laser.

Effect of laser energy density on microstructure and properties Cu–Fe–P immiscible alloys fabricated by laser selective melting: heterogeneous and high strength and magnetic

Through the incorporation of phosphorus (P) as a third component, an in-situ formation of a magnetic phase with a nanotwin structure was achieved. The utilization of selective laser melting (SLM) enabled the synthesis of a Cu–Fe–P immiscible alloy that exhibits an integrated structure and function. The microstructure predominantly consists of a magnetic heterogeneous Fe–P-rich phase, comprising a mixture of Fe2P and a small quantity of Fe3P, which is distributed within the ε-Cu Cu-rich matrix in alternating “fiber-layer” and “particle-shape” forms. Additionally, the fibrous Fe2P phase exhibited precipitation of α-Fe, while the Fe–P-rich phase experienced the precipitation of high-density nanotwinned Cu (nt-Cu) particles. The microstructure density and structural characteristics of Cu–Fe–P immiscible alloys were enhanced through the adjustment of laser energy density, leading to improvements in their mechanical and magnetic properties. It was observed that the microstructure density initially increased and then decreased with increasing laser energy density. The highest relative density of the Cu–Fe–P immiscible alloy microstructure (98%) was achieved at a laser energy density of 53 J/mm3. Furthermore, the influence of laser energy density on the mechanical and soft magnetic properties of Cu–Fe–P immiscible alloys was examined. The findings indicate that the mechanical and soft magnetic properties of these alloys are affected by the laser energy density. The findings indicate that the compact Cu–Fe–P immiscible alloys exhibit favorable compression mechanical properties and soft magnetic properties. Specifically, the ultimate compressive stress can reach 890.5 ± 20 MPa, while the failure strain can reach 20.5 ± 2%. Additionally, the coercivity is observed to be as low as 20.0 Oe, the magnetic saturation strength as high as 93.5 emu/g, and the residual magnetization at 1.1 emu/g.

Enhancing the forming quality of Al2024-T351 sheets in laser peen forming through a novel energy sequence arrangement strategy

Laser peen forming (LPF) employs laser-induced shock waves for shaping and modifying bent structures, exhibiting high flexibility and non-contact advantages. This study investigated the impact of different laser energies, laser peening sequences, and energy sequences on the bending deformation, surface quality, and stress distribution of 4 mm thick sheets, using both experiments and simulations. Increasing laser energy and peening sequences were found to enhance the degree of sheet deformation, while adjusting the energy sequence had an insignificant effect on deformation. Higher laser energy resulted in increased surface roughness in the peened area, whereas increasing the peening sequence reduced surface roughness. The optimal approach for reducing surface roughness in forming sheets was found to be utilizing low-energy peening after high-energy peening (high-then-low). Moreover, compared to single low-energy peening, employing the high-then-low-energy peening strategy decreased the attenuation rate of the compressive stress wave, which led to a 23.5 % increase in the magnitude and 25 % increase in the depth of the final compressive stress. The compressive residual stress (CRS) in the length and width direction of the sheet's surface layer was higher with the high-then-low energy peening strategy compared to other treatment strategies.

Experimental Study on the Initial Current Characteristics of Laser-Triggered Vacuum Switch During Trigger Process

The trigger characteristics of the laser-triggered vacuum switch (LTVS) are significantly affected by the parameters of the laser-produced initial current. In this paper, a low operating voltage is applied across LTVS, and the trigger experiments are carried out under different laser energy and operating voltage. The initial current is obtained by measuring the voltage drop across a 25 Ω resistor. The influence of laser energy and operating voltage on the trigger characteristics can be characterized by the parameters of the initial current, such as the current peak value, the number of charges released, the rate of rise, and the delay time. The experimental results show that an increase in laser energy can increase the current peak value, the number of charges released, and the rate of rise, and can decrease the delay time. These results show that an increase in laser energy helps the LTVS trigger process. The external electric field is much smaller than the laser electric field. Hence, only the current peak value is affected by the operating voltage, and the impact on the other current parameters is weak.

Assessment of burner structure for methane-oxygen inverse diffusion flame based on laser detection: Reaction characteristics and soot analysis

The structure of a burner is a key issue of boilers and gasifiers in several industries. It significantly influences the flame formation and combustion reaction determining the mixing degree of fuel and oxidant. This study aims to explore the characteristics of flames at different angles and evaluate their advantages in specific applications. The present work explores the correlation between laser-induced breakdown threshold energy and flame temperature based on laser-induced breakdown spectroscopy (LIBS). Subsequently, the local structure and reaction characteristics of the flame at different burner angles (45, 60 and 90°) were investigated with simulation. The local equivalence ratio of the laminar flame was used to determine the distribution of reactants and components in the flame. The results indicated that the breakdown threshold energy was positively correlated with the temperature of the flame, and it was dependent on the gas concentration. With increased laser energy, the O/H ratio could be used as a function of the local equivalence ratio of the flame. In addition, the study of flame images and the spontaneous radiation of soot revealed that the C/H ratio in the flame reached the maximum value when the burner incident angle was 45°. Through simulation and experimental research, we found that the flame at 60° angle is the most stable, produces the least soot, has the highest combustion efficiency, and has better thermal radiation intensity.