Search Results (60)

Background: Successful healing of chronic apical periodontitis after endodontic treatment requires a reduction in the size of the radiolucent area and the healing of the bone. This study aimed to compare the effects of different irrigation activation techniques on healing in single-rooted mandibular premolar teeth with periapical lesions of endodontic origin. Methods: A total of 132 systemically healthy patients with mandibular single-rooted premolar teeth and a periapical index (PAI) score ≥ 3 were assigned to five experimental groups (Sonic activation, Passive ultrasonic irrigation, Photon-Induced Photoacoustic Streaming, Shock Wave Enhanced Emission Photoacoustic Streaming and Manual dynamic activation) and a control group (Conventional Syringe Irrigation). After access cavity preparation, the canals were prepared up to three sizes larger than the initial apical diameter with 5 mL of 2.5% NaOCl used between each file. Final irrigation was performed via the assigned activation system. The root canals were obturated with gutta-percha in a single visit. The effects of the activation systems on healing were compared at 1-year follow-up. The primary outcome measure was the change in lesion diameter. PAI score and fractal dimension (FD) were evaluated as secondary outcomes. Results: At the 1-year follow-up, FD values significantly increased, PAI scores and lesion size decreased in all groups compared with baseline (p < 0.001). However, the increase in FD was comparable among the irrigation groups (p > 0.05). In contrast, lesion size reduction and PAI-based healing rates favored the laser-activated groups. The PAI scores and lesion size in the control group were significantly greater than that in the laser groups (p < 0.05). Conclusions: At the 1-year follow-up, all the groups presented similar FD increases, while the laser irrigation groups presented significantly greater reductions in lesion size than did the control group. Full article

This study aims to reveal the mechanism of a novel method for fabricating hierarchical microstructured hydrophobic surfaces. Specifically, plasma shock waves induced by laser ablation are applied to the workpiece to replicate the microstructures on the mold surface, thus obtaining primary microstructures. Meanwhile, the material splashing effect induced by laser ablation is utilized to form secondary microstructures on the basis of the primary microstructures. Subsequently, fluorination treatment and aging treatment are adopted to alter the chemical composition of the hierarchical microstructures on the workpiece surface, thereby reducing the surface energy and enhancing hydrophobicity. In addition, this study investigates the effects of a different number of laser shocks, laser fluence and mold periods on the forming results. Under a laser fluence of 28.97 J/cm², within the range of one to five laser shocks, the forming effect of the aluminum foil workpiece improves with the increase in the number of laser shocks. When the number of laser shocks is set to 3, within the laser fluence range of 19.1–76.39 J/cm², the forming result of the aluminum foil workpiece is enhanced as the laser fluence increases. The larger the mold period, the better the forming effect of the workpiece. An analysis of aging treatment and fluorination treatment reveals their impacts on the workpiece through assessments of wettability, surface chemical composition, and surface morphology. The findings reveal that both aging and fluorination treatments significantly enhance the contact angle of the aluminum foil workpiece, all while preserving its original surface structure. The main changes occur in terms of element content and chemical composition, and a large number of non-polar groups are generated on the workpiece surface after the modification treatments. Full article

Combined pulse laser systems combining continuous-wave (CW) lasers and nanosecond pulsed lasers have shown clear advantages in metal ablation and surface modification. However, the plasma shielding effect induced by nanosecond pulses and the associated shock-wave phenomena in hybrid laser systems remain insufficiently investigated, particularly regarding their influence on CW laser energy coupling. In this study, the ablation behavior of metal targets under the combined irradiation of a 500 W CW laser and nanosecond pulsed lasers with pulse energies ranging from 0.4 J to 1.0 J was investigated. High-speed plasma imaging was employed to analyze laser–material interaction characteristics, including absorption behavior and molten material ejection, while high-speed infrared thermography was used to monitor transient temperature evolution during combined pulse laser processing. Macroscopic and microscopic analyses were conducted to characterize damage morphology, and a three-dimensional surface profilometer was used to quantitatively evaluate ablation efficiency. The results show that, under combined pulse laser irradiation, the removed volume increased from 0.05 mm³ to 0.618 mm³ and the ablation depth increased from 0.136 mm to 0.776 mm. Compared with CW laser processing alone, the ablation efficiency was markedly enhanced. This improvement is attributed to the combined effects of optimized energy deposition, thermal distribution, and material response. In addition, the plasma shielding effect was observed to vary with nanosecond pulse energy, indicating that precise energy control is critical for performance enhancement. This study demonstrates the potential of combined pulse laser technology for high-efficiency and high-precision metal surface processing and micro–nano fabrication. Full article

The control of mechanical effects, such as shock waves, induced by ultrashort laser pulses in water is crucial for applications in biomedicine and material processing. However, optimizing these effects requires a detailed understanding of how laser parameters, particularly pulse duration, influence the underlying energy deposition mechanisms. This study systematically investigates the dependence of shock wave amplitude on fluence (up to 10 J/cm²) and pulse duration (200 fs to 10 ps) of near-infrared laser pulses under tight focusing conditions (Numerical aperture NA = 0.42), using a combined experimental and numerical approach based on the dynamical rate equation model. Our key finding is that the shock wave amplitude is governed by the total kinetic energy of the electrons in the laser-induced plasma, leading to a distinct maximum at approximately 5 ps (confidence interval: 4.5–5.5 ps) and saturation at fluences ~7 J/cm². This optimum arises from a balance between the increasing effectiveness of avalanche ionization for longer pulses and the competing effects of electron recombination and reduced photoionization efficiency. Consequently, these results identify a practical parameter window—pulse durations of 4–6 ps at moderate fluences—for optimizing laser-induced mechanical effects in applications such as laser surgery in aqueous media. Full article

This study systematically examined shock wave velocity induced by millisecond–nanosecond combined-pulse laser (ms–ns CPL) at a fixed ns laser energy density of 6 J/cm², exploring the effects of varying pulse delays of 0 to 3 ms and ms laser energy densities of 226.13 J/cm², 301 J/cm² and 376.89 J/cm². The temporal evolution of shock wave velocity induced by varying laser parameters was predicted by an attention mechanism-based long short-term memory algorithm (Attention-LSTM). The dependence between laser parameters and the evolution of shock wave velocity was captured by the LSTM layer. An attention mechanism was utilized to adaptively increase the weights of important time points during the propagation of the shock wave, thereby improving prediction accuracy. The experimental data corresponding to ms laser energy densities of 226.13 J/cm² and 301 J/cm² were set as the training set. The ms laser energy density of 376.89 J/cm² experimental data was set as test set to evaluate the generalization ability of the model under unknown ms laser energy. The results indicate that when ms laser energy density is 376.8 J/cm², the pulse delay is 2.2 ms. The shock wave velocity induced by the CPL increased by 50.77% compared with that induced by a single ns laser. The proposed Attention-LSTM model effectively predicts the evolutionary characteristics of shock wave velocity. The mean absolute error (MAE), root mean square error (RMSE), mean bias error (MBE) and the correlation coefficient (R²) of the test set are 7.65, 9.01, 1.47 and 0.98, respectively. This study provides a new data-driven approach for predicting the shock wave behavior induced by combined laser parameters and provides valuable guidance for optimizing laser process parameter combinations. Full article

This study employs the simultaneous phase-shift interferometry (SPSI) system to diagnose laser-induced plasma (LIP) and shock wave (SW). In high-density LIP diagnostics, the Faraday rotation effect causes probe light polarization deflection, rendering traditional fixed-phase-demodulation methods ineffective, the Carré phase-recovery algorithm is adopted and its applicability is verified. Uncertainty analysis and precision verification show that the total phase shift uncertainty is controlled within 0.045 radians, equivalent to a refractive index accuracy of $8.55\times {10}^{-6}$, with sensitivity to weak perturbations improved by approximately one order of magnitude compared to conventional carrier-frequency interferometry. Experimental results demonstrate that the SPSI system precisely captures the initial spatiotemporal evolution of LIP and tracks shock waves at varying attenuation levels, exhibiting notable advantages in weak shock wave detection. This research validates the SPSI system’s high sensitivity to transient weak perturbations, offering a valuable diagnostic tool for high-vacuum plasmas, low-pressure shock waves, and stress waves in optical materials. Full article

Background: The quest for minimally invasive disinfection in endodontics has led to using Erbium:Yttrium-Aluminum-Garnet (Er:YAG) lasers. Conventional approaches may leave bacterial reservoirs in complex canal anatomies. Er:YAG’s strong water absorption generates photoacoustic streaming, improving smear layer removal with lower thermal risk than other laser systems. Methods: This systematic review followed PRISMA 2020 guidelines. Database searches (PubMed/MEDLINE, Embase, Scopus, Cochrane Library) identified studies (2015–2025) on Er:YAG laser-assisted root canal disinfection. Fifteen articles met the inclusion criteria: antibacterial efficacy, biofilm disruption, or smear layer removal. Data on laser settings, irrigants, and outcomes were extracted. The risk of bias was assessed using a ten-item checklist, based on guidelines from the Cochrane Handbook for Systematic Reviews of Interventions. Results: All studies found Er:YAG laser activation significantly improved root canal disinfection over conventional or ultrasonic methods. Photon-induced photoacoustic streaming (PIPS) and shock wave–enhanced emission photoacoustic streaming (SWEEPS) yielded superior bacterial reduction, especially apically, and enabled lower sodium hypochlorite concentrations without sacrificing efficacy. Some research indicated reduced post-operative discomfort. However, protocols, laser parameters, and outcome measures varied, limiting direct comparisons and emphasizing the need for more standardized, long-term clinical trials. Conclusions: Er:YAG laser-assisted irrigation appears highly effective in biofilm disruption and smear layer removal, supporting deeper irrigant penetration. While findings are promising, further standardized research is needed to solidify guidelines and confirm Er:YAG lasers’ long-term clinical benefits. Full article

A new method of producing metal powders for additive manufacturing by the atomization of free-falling melt streams using pulsed cross-flow gaseous shock or detonation waves is proposed. The method allows the control of shock/detonation wave intensity (from Mach number 4 to about 7), as well as the composition and temperature of the detonation products by choosing proper fuels and oxidizers. The method is implemented in laboratory and industrial setups and preliminarily tested for melts of three materials, namely zinc, aluminum alloy AlMg5, and stainless steel AISI 304, possessing significantly different properties in terms of density, surface tension, and viscosity. Pulsed shock and detonation waves used for the atomization of free-falling melt streams are generated by the pulsed detonation gun (PDG) operating on the stoichiometric mixture of liquid hydrocarbon fuel and gaseous oxygen. The analysis of solidified particles and particle size distribution in the powder is studied by sifting on sieves, optical microscopy, laser diffraction wet dispersion method (WDM), and atomic force microscopy (AFM). The operation process is visualized by a video camera. The minimal size of the powders obtained by the method is shown to be as low as 0.1 to 1 μm, while the maximum size of particles exceeds 400–800 μm. The latter is explained by the deficit of energy in the shock-induced cross-flow for the complete atomization of the melt stream, in particular dense and thick (8 mm) streams of the stainless-steel melt. The mass share of particles with a fraction of 0–10 μm can be at least 20%. The shape of the particles of the finest fractions (0–30 and 30–70 μm) is close to spherical (zinc, aluminum) or perfectly spherical (stainless steel). The shape of particles of coarser fractions (70–140 μm and larger) is more irregular. Zinc and aluminum powders contain agglomerates in the form of particles with fine satellites. The content of agglomerates in stainless-steel powders is very low. In general, the preliminary experiments show that the proposed method for the production of finely dispersed metal powders demonstrates potential in terms of powder characteristics. Full article

The present study investigates the impact of the electrode surface roughness on the electrofreezing of water. This research focuses on how the electrode microstructure induced by a laser treatment affects the nucleation and growth of ice crystals under controlled electric fields. For this, electrofreezing experiments of deionized water over electrodes with varying surface roughnesses and crystalline textures were conducted. The electrodes of the Al6061 T6 alloy were microstructured via the Laser Shock Processing (LSP) method. For this purpose, the pulse densities during the LSP process were varied (900, 1600, and 2500 pulses/cm²). The increase in pulse density was correlated to the microstructural features and average roughness of the LSP-treated Al6061 alloy. A wave-like microstructure was induced upon the LSP treatment, with roughnesses between 3.5 and 6 µm at the selected pulse densities. The results indicate that electrode roughness significantly influences the electrofreezing process. Rougher electrodes were found to increase the nucleation temperature, suggesting enhanced ice nucleation activity. These findings are attributed to the increased electric field concentration at the asperities of the rough surfaces and the (111) planes of the Al6061 alloy, which may facilitate the alignment of water molecules and the formation of critical ice nuclei. Full article

In order to study the feasibility of forming microtexture at the surface of 7050 aluminum alloy by laser-induced cavitation bubble, and how the density of microtexture influences its tribological properties, the evolution of the cavitation bubble was captured by a high-speed camera, and the underwater acoustic signal of evolution was collected by a fiber optic hydrophone system. This combined approach was used to study the effect of the cavitation bubble on 7050 aluminum alloy. The surface morphology of the microtexture was analyzed by a confocal microscope, and the tribological properties of the microtexture were analyzed by a friction testing machine. Then the feasibility of the preparation process was verified and the optimal density was obtained. The study shows that the microtexture on the surface of a sample is formed by the combined results of the plasma shock wave and the collapse shock wave. When the density of microtexture is less than or equal to 19.63%, the diameters of the micropits range from 478 μm to 578 μm, and the depths of the micropits range from 13.56 μm to 18.25 μm. This shows that the laser-induced cavitation bubble is able to form repeatable microtexture. The friction coefficient of the sample with microtexture is lower than that of the untextured sample, with an average friction coefficient of 0.16. This indicates that the microtexture formed by laser-induced cavitation bubble has a good lubrication effect. The sample with a density of 19.63% is uniform and smooth, having the minimum friction coefficient, with an average friction coefficient of 0.14. This paper provides a new approach for microtexture processing of metal materials. Full article

To investigate the feasibility and formation laws of fabricating micro-dimples induced by near-wall laser-induced cavitation bubble (LICB) on 7050 aluminum alloy. A high-speed camera and a fiber-optic hydrophone system were used to capture pulsation evolution images and acoustic signals of LICB. Meanwhile, a three-dimensional profilometer was employed to examine the contour morphology of the surface micro-dimple on the specimen. The results show that at an energy level of 500 mJ, the total pulsation period for the empty bubble is 795 μs, with individual pulsation periods of 412.5 μs, 217 μs, and 165 μs for the first, second, and third cycles, respectively, with most energy of the laser and bubble being consumed during the first evolution period. Under the synergy of the plasma shock wave and collapse shock wave, a spherical dimple with a diameter of 450 μm is formed on the sample surface with copper foil as the absorption layer. A model of micro-dimple formed by LICB impact is established. As the energy increases, the depth of the surface micro-dimple peaks at an energy of 400 mJ and then decreases. The depth of the surface micro-dimple increases with the increase in the number of impacts; the optimal technology parameters for the micro-dimple formation by LICB impact are as follows: the absorption layer is copper foil, the energy is 400 mJ, and the number of impacts is three. Full article

Herein, we present the results of an experimental study on the mechanical properties of Fe-C alloys with different carbon contents (0.2, 0.45, and 0.8%) in a wide range of deformation rates (10⁻³–10³ s⁻¹) and abrasive wear resistance, which underwent combined laser thermal (laser surface hardening—LSH) and laser shock wave (Laser Shock Peening—LSP) processing. The combined treatment modes included a different sequence of exposure to laser thermal and laser-induced shock pulses on the material. The amplitude and duration of laser-induced shock waves were measured using a laser Michelson interferometer. The mechanical properties of steel samples were studied under conditions of uniaxial tension under static loads on a standard universal testing machine, the LR5KPlus, and under dynamic loading, tests were carried out on a specialized experimental complex according to the H. Kolsky method using a split Hopkinson rod. The abrasive wear resistance of hardened surfaces was studied using the Brinell–Haworth method. Studies have shown that the use of a combination of LSH and LSP treatments leads to an increase in both the mechanical properties of steels and abrasive wear resistance compared to traditional laser hardening. It has been established that in the combinations considered, the most effective is laser treatment, in which LSP treatment is applied twice: before and after LSH. Thus, after processing steels using this mode, an increase in the depth of the hardened layer was recorded—by 1.53 times for steel 20, by 1.41 times for steel 45, and by 1.29 times for steel U8—as well as a maximum increase in microhardness values by 22% for steel 20, by 27% for steel 45, and by 13% for U8 steel. The use of this mode made it possible to obtain the maximum strength properties of the studied materials under static and dynamic loading, which is associated with an increase in the volume fraction of the strengthened metal and high microhardness values of the strengthened layer of traditional LSH. The dependences of abrasive wear of the studied steels after various combinations of LSP and LSH impacts were established. It is shown that the greatest wear resistance of the studied steels is observed in the case when the LSH pulse is located between two LSP pulses. In this case, abrasive wear resistance increases by 1.5–2 times compared to traditional LSH. Full article

This paper presents a numerical study on the laser shock wave propagation in a 3D woven carbon-fiber-reinforced polymer (CFRP) material by means of detailed and homogenized finite element (FE) models. The aim of this study is to numerically characterize the shock wave response of the 3D woven CFRP in terms of back-face velocity profiles and the induced damage, and to investigate whether the detailed FE models could be effectively replaced by homogenized FE models. The 3D woven geometry was designed using the TexGen 3.13.1 software, while the numerical analyses were executed using the R11.0.0 LS-Dyna explicit FE software. A high-strain-rate behavior was considered for the matrix. The fiber bundles in the detailed models were modeled as a high-fiber-content unidirectional composite laminate, with its mechanical properties calculated by micromechanical equations. A progressive damage material model was applied to both the fiber bundles of the detailed model and the homogenized models. The results of the detailed model reveal a considerable effect of the material’s architecture on the shock wave propagation and sensitivity of the back-face velocity profile to the spot location. Consequently, the homogenized model is not capable of accurately simulating the shock wave response of the 3D woven composite. Moreover, the detailed model predicts matrix cracking in the resin-rich areas and in the bundles with high accuracy, as well as fiber failure. On the contrary, the homogenized model predicts matrix cracking in the same areas and no fiber failure. Full article

With the rapid development of the advanced manufacturing industry, equipment requirements are becoming increasingly stringent. Since metallic materials often present failure problems resulting from wear due to extreme service conditions, researchers have developed various methods to improve their properties. Laser shock peening (LSP) is a highly efficacious mechanical surface modification technique utilized to enhance the microstructure of the near-surface layer of metallic materials, which improves mechanical properties such as wear resistance and solves failure problems. In this work, we summarize the fundamental principles of LSP and laser-induced plasma shock waves, along with the development of this technique. In addition, exemplary cases of LSP treatment used for wear resistance improvement in metallic materials of various nature, including conventional metallic materials, laser additively manufactured parts, and laser cladding coatings, are outlined in detail. We further discuss the mechanism by which the microhardness enhancement, grain refinement, and beneficial residual stress are imparted to metallic materials by using LSP treatment, resulting in a significant improvement in wear resistance. This work serves as an important reference for researchers to further explore the fundamentals and the metallic material wear resistance enhancement mechanism of LSP. Full article

This work focused on the experimental characterization of a complex flow structure behind a cross-flow array of cylindrical pins installed on the wall of a supersonic duct. This geometry simulates several common gas dynamic configurations, such as a supersonic mixer, a turbulence-generating grid, or, to some extent, a grid fin. In this work, the instrumentation employed is essentially non-intrusive, including spanwise integrating techniques such as (1) fast schlieren visualization and (2) Shack–Hartmann wavefront sensors; and planar techniques, namely (3) acetone Mie scattering and (4) acetone planar laser-induced fluorescence. An analysis of the data acquired by these complementary methods allowed the reconstruction of a three-dimensional portrait of supersonic flow interactions with a discrete pin array, including the shock wave structure, forefront separation zone, shock-induced separation zone, shear layer, and the mixing zone behind the pins. The main objective of this activity was to use various visualization techniques to acquire essential details of a complex compressible flow in a wide range of temporal–spatial scales. Particularly, a fine structure in the supersonic shear layer generated by the pin tips was captured by a Mie scattering technique. Based on the available publications, such structures have not been previously identified or discussed. Another potential outcome of this work is that the details revealed could be utilized for adequate code validation in numerical simulations. Full article