- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
Propulsion effects after laser ablation in water, confined by different geometries
摘要： A Nd:YAG laser with 7-ns pulses and pulse energies up to 10 mJ is used to induce an optical breakdown in the front surface of an aluminum rod, covered by a water layer. The rod is part of a ballistic pendulum. In this way, we study the propulsion effects by means of coupling coefficient and energy-conversion efficiency with respect to different confining geometries, volumes of water applied to the front surface of the rod, and the distance of this surface from the laser-beam focus. Holes with different dimensions are drilled on the target surface and filled with different volumes of water to examine the influence of the confinement by the liquid (a free boundary) and a solid-surface geometry on laser ablation effects. The rod movement and the water ejection after laser ablation are acquired by a high-speed camera with 10k frames per second. The results show that the confinement by cavity substantially increases the propulsion effects by shaping the ejected flow of the liquid; while the cavitation bubble, induced inside the water layer, plays a significant role in propulsion efficiency. From the presented results, it follows that the laser-propelled rod carries below 0.5% of the total mechanical energy after propulsion, while the rest of this energy represents the kinetic energy of the ablated water. As expected, moving the target surface away from the focal position decreases the ablative-propulsion efficiency. When the focus is moved inside the solid target, the decrease occurs due to lower conversion of the pulse energy into the energy of the cavitation bubble. If the focus is moved from the surface outward, the bubble moves towards the liquid–gas interface and it is not able to efficiently eject all the liquid from the target.
关键词： Cavitation bubble,Coupling coefficient,Laser propulsion,Nanosecond laser,Energy-conversion efficiency,Laser ablation
更新于2025-09-23 15:21:01
-
Laser cavitation peening of gray cast iron: Effect of coverage layer on the surface integrity
摘要： Copper coverage layer was employed to the laser cavitation peening (LCP) of HT200 gray cast iron. The process of bubble evolution, velocity field of bubble, impact of water-jet, deformation and stress of material were simulated. The effects of coverage layer on the surface integrity (surface morphology and roughness, residual stress, micro-hardness) of LCP treated HT200 under various laser energies and defocusing amounts were systemically investigated. The results indicate that the maximum velocity of water-jet is 380 m/s and the diameter is 0.1 mm. The surface roughness of HT200 increases after the treatment of LCP. The presence of Copper coverage layer makes the HT200 surface more flat and the surface roughness decreases by half. At the case of no coverage layer, the parameters of 200 mJ laser energy and 1 mm defocusing amount are optimal for roughness, compressive residual stress and micro-hardness. Higher laser energy produces higher magnitude of micro-hardness and compressive residual stress in the case of coverage layer, and the optimal defocusing amount is 0 mm.
关键词： Coverage layer,surface integrity,simulation,Laser cavitation peening,HT200 gray cast iron
更新于2025-09-23 15:21:01
-
Characteristics of Bubble Oscillations During Lasera??Activated Irrigation of Root Canals and Method of Improvement
摘要： Background and Objectives: Laser‐activated irrigation of dental root canals is being increasingly used as its efficacy has been shown to be superior compared with conventional techniques. The method is based on laser‐initiated localized fluid evaporation and subsequent rapid bubble expansions and collapses, inducing microfluid flow throughout the entire volume of the cavity. The irrigation efficacy can be further improved if optimally delayed “SWEEPS” double laser pulses are delivered into the canal. This study aims to show that the irrigation efficacy, as measured by the induced pressure within the canal, is related to the double pulse delay, with the maximal pressure generated at an optimal delay. The second aim is to find a method of determining the optimal delay for different cavity dimensions and/or laser parameters. Study Design/Materials and Methods: Experiments were made in transparent models of root canals where Er:YAG laser (λ = 2.94 μm, pulse duration tp = 25 or 50 microseconds, and pulse energies up to EL = 40 mJ) was used with a combination of cylindrical and conical fiber‐tip geometries (diameters 400 and 600 μm). High‐speed photography (60,000 fps) and average pressure measurements inside the canal were used for process characterization. Results: The results show that a pressure amplification of more than 1.5 times occurs if the laser pulse delay approximately coincides with the bubble oscillation time. Correlations between normalized oscillation time and canal diameter for a wide range of laser pulse energies (R2 = 0.96) and between the average pressure within the canal and the bubble oscillation periods (R2 = 0.90) were found. A relationship between the bubble oscillation time and the diameter of the treated cavity was found depending on the bubble oscillation time in an infinite fluid reservoir. Conclusions: The bubble oscillation time within a constrained volume can be determined based on the known oscillation time in infinite space, which offers a fast and simple solution for optimization of the laser parameters. These findings enable determination of optimal conditions for shock wave generation, and improvement of root canal irrigation at the same dose of laser energy input, leading to improved treatment efficacy and safety.
关键词： constrained environments,cavitation bubble,irrigation,Er:YAG laser,root canals,laser‐activated,laser‐induced cavitation
更新于2025-09-23 15:19:57
-
Cavitation inception pressure and bubble cloud formation due to the backscattering of high-intensity focused ultrasound from a laser-induced bubble
摘要： Cavitation bubble cloud formation due to the backscattering of high-intensity focused ultrasound (HIFU) from a laser-induced bubble in various water temperatures and dissolved oxygen (DO) has been investigated. A laser-induced bubble generated near the geometrical focus of HIFU is utilized to yield intense negative pressure by the backscattering. Optical observation with a high-speed video camera and pressure measurement with a fiber-optic probe hydrophone are conducted simultaneously to understand the forming process of a bubble cloud and corresponding pressure field by the backscattering. Optical observation shows that a bubble cloud grows stepwise forming multiple layers composed of tiny cavitation bubbles, and the cavitation inception position is consistent with the local minimum pressure position simulated with the ghost fluid method. The bubble cloud grows larger in the opposite direction of HIFU propagation, and the absolute value of the cavitation inception pressure decreases with an increase in water temperature. The linear correlation between cavitation inception pressure and water temperature agrees with that given by Vlaisavljevich, Xu, Maxwell, Mancia, Zhang, Lin, Duryea, Sukovich, Hall, Johnsen, and Cain [IEEE Trans. Ultrason. Ferroelectr. Freq. Control 63, 1064–1077 (2016)]. However DO has minor dependence on the cavitation inception pressure when DO is degassed sufficiently. Furthermore, the gas nucleus size that might exist in the experiment has been estimated by using bubble dynamics.
关键词： Dissolved oxygen,Water temperature,Bubble cloud formation,Cavitation inception pressure,Laser-induced bubble,High-intensity focused ultrasound,Cavitation
更新于2025-09-23 15:19:57
-
Plasma charging effect on the nanoparticles releasing from the cavitation bubble to the solution during nanosecond Pulsed Laser Ablation in Liquid
摘要： The laser induced plasma during the nanosecond Pulsed Laser Ablation in Liquid (PLAL) plays a crucial role in the nanoparticles (NPs) formation and charging. It was demonstrated that during the plasma phase evolution, once the NPs are formed, they are charged with the excess of plasma electrons. Immediately after the plasma phase extinguishes, the NPs will be released in the induced vapor bubble, generated by the fast energy exchanges between the plasma and the liquid. The excess of charge in the NPs preserves them from the agglomeration during the bubble evolution and can induces an electrostatic pressure able to eject the particles outside the cavitation bubble. In this work, the plasma charging effect on the particle releasing in solution, during the bubble evolution, has been investigated. Temporal evolution of laser induced bubble on silver target immersed in water has been measured with the shadowgraph technique. Then, starting from the experimental bubble radius evolution, the releasing of the NPs from the cavitation bubble to the liquid has been modeled by comparing the electrostatic pressure of the charged NPs cloud and the pressure of the cavitation bubble. The following discussion proposes a new insight of the mechanism of NPs releasing in solution.
关键词： Laser Ablation Synthesis in Solution (LASIS),Cavitation bubble,NPs releasing,Pulsed Laser Ablation in Liquid (PLAL),NP formation
更新于2025-09-23 15:19:57
-
Soft material perforation via double-bubble laser-induced cavitation microjets
摘要： The resulting jet of two interacting laser-induced cavitation bubbles is optimized and studied as a technique for micro-scale targeting of soft materials. High controllability of double-bubble microjets can make such configurations favorable over single bubbles for applications where risk of ablation or thermal damage should be minimized such as in soft biological structures. In this study, double-bubble jets are directed toward an agar gel-based skin phantom to explore the application of micro-scale injection and toward a soft paraffin to quantify the targeting effectiveness of double-bubble over single-bubble jetting. The sharp elongation during the double-bubble process leads to fast, focused jets reaching average magnitudes of Ujet = 87.6 ± 9.9 m/s. When directed to agar, the penetration length and injected volume increase at ～250 μm and 5 nl per subsequent jets. Such values are achieved without the use of fabricated micro-nozzles seen in existing needle-free laser injection systems. In soft paraffin, double-bubble jetting produces the same penetration length as single-bubble jetting, but with ～45% reduction in damage area at a 3× greater target distance. Thus, double-bubble jetting can achieve smaller impact areas and greater target distances, potentially reducing collateral thermal damage and effects of strong shockwave pressures.
关键词： microjets,double-bubble jetting,soft materials,laser-induced cavitation,needle-free injection
更新于2025-09-23 15:19:57
-
[Laser Institute of America ICALEO?? 2017: 36th International Congress on Applications of Lasers & Electro-Optics - Atlanta, Georgia, USA (October 22a??26, 2017)] International Congress on Applications of Lasers & Electro-Optics - A composite stellite alloy hardfacing with improved laser cladding behavior and wear resistance
摘要： To solve the existing wear and corrosion problems in power generation industry, this research investigates the wear and corrosion behavior of Stellite alloys in NaOH solution, which simulates the amine media in the feedwater service of power generation plants. The Stellite alloys under this study include Stellite 6 and a composite Stellite alloy. The composite Stellite alloy hardfacing, which consists of 70% Stellite 3 and 30% Stellite 21, is created via laser cladding for control valve seat sealing surfaces, aiming at enhancing hardness and wear resistance, compared with Stellite 6 hardfacing, and improving cracking in laser cladding process, compared with Stellite 3. The composite Stellite alloy hardfacing is made on 316 stainless steel substrate and it does not show any cracking. The microstructure of the hardfacing is analyzed using SEM, EDS and XRD. The hardness, dry sliding wear resistance and cavitation-erosion resistance in NaOH solution are evaluated. Stellite 6 hardfacing is prepared with the same laser process parameters and is also analyzed and tested under the same conditions with the composite Stellite alloy hardfacing for comparison. The experimental results and real industrial test demonstrate superior performance of the composite Stellite alloy hardfacing to Stellite 6 hardfacing for control valve seat sealing application.
关键词： Cavitation-erosion,Hardfacing via laser cladding,Stellite alloy,Dry-sliding wear
更新于2025-09-23 15:19:57
-
Surface functionalization by nanosecond-laser texturing for controlling hydrodynamic cavitation dynamics
摘要： The interaction between liquid flow and solid boundary can result in cavitation formation when the local pressure drops below vaporization threshold. The cavitation dynamics does not depend only on basic geometry, but also on surface roughness, chemistry and wettability. From application point of view, controlling cavitation in fluid flows by surface functionalization is of great importance to avoid the unwanted effects of hydrodynamic cavitation (erosion, noise and vibrations). However, it could be also used for intensification of various physical and chemical processes. In this work, the surfaces of 10-mm stainless steel cylinders are laser textured in order to demonstrate how hydrodynamic cavitation behavior can be controlled by surface modification. The surface properties are modified by using a nanosecond (10–28 ns) fiber laser (wavelength of 1060 nm). In such a way, surfaces with different topographies and wettability were produced and tested in a cavitation tunnel at different cavitation numbers (1.0–2.6). Cavitation characteristics behind functionalized cylindrical surfaces were monitored simultaneously by high-speed visualization (20,000 fps) and high frequency pressure transducers. The results clearly show that cavitation characteristics differ significantly between different micro-structured surfaces. On some surfaces incipient cavitation is delayed and cavitation extent decreased in comparison with the reference – a highly polished cylinder. It is also shown that the increased surface wettability (i.e., hydrophilicity) delays the incipient cavitation.
关键词： Surface engineering,Laser texturing,Hydrodynamic cavitation,Fluid dynamics,Hydrophobic/hydrophilic surface
更新于2025-09-23 15:19:57
-
Laser-generated focused ultrasound transmitters with frequency-tuned outputs over sub-10-MHz range
摘要： Previous laser-generated focused ultrasound (LGFU) systems have been operated with >15 MHz frequency, allowing for high spatial precision (<100 lm). However, they have been limited only to proximal biomedical applications ex vivo with treatment depths smaller than 10 mm from the lens surface. Although the low-megahertz frequency operation has the advantage of a longer range of therapy, this requires a proper photoacoustic lens made of a nanocomposite coating over a spherically curved substrate whose transmission layer is physically designed for frequency-tuned outputs. This demands a fabrication method that can provide such a nanocomposite structure. We demonstrate photoacoustic lenses operated in an unexplored frequency range of 1–10 MHz, which can simultaneously produce high-amplitude pressure outputs suf?cient for pulsed acoustic cavitation. We physically design a spatially elongated photoacoustic output and then fabricate a transmitter by controlling the density of light-absorbing nanoscale elements in a solution form and by using a replica mold to shape the lens curvature. Our approach is validated by fabricating and characterizing planar transmitters and then applied to focal con?gurations. This offers various possibilities for LGFU-based treatments (e.g., pulsed cavitational therapy such as histotripsy) over the low-megahertz frequency range, which has not been realized by conventional LGFU systems.
关键词： laser-generated focused ultrasound,sub-10-MHz range,frequency-tuned outputs,photoacoustic lenses,acoustic cavitation
更新于2025-09-19 17:13:59
-
Opto-acoustic effect of Au nanoparticles in water under irradiation of pulse laser
摘要： The cavitation bubbles in water generated by laser irradiated Au nanoparticles (NPs) exhibit potential applications in the photothermal therapy and enhancing photoacoustic imaging. The exploration of the related processes is crucial to improve the opto-acoustic efficiency that is important to these applications. Herein a model including the Mie theory, gas state equation, Rayleigh-Plesset equation, and sound pressure equation is established. Through this model, the volume and pressure of the bubble is obtained. The influences of laser flux and NP diameter to the volume and pressure of the bubble are simulated based on this model. The acoustic pressure of many Au NPs is obtained through the superposition of the opto-acoustic wave of a single Au NP, in which the Au NPs are assumed to be distributed randomly in the laser irradiation area. The opto-acoustic wave of many Au NPs is also investigated experimentally, which coincides with the theoretical analyses.
关键词： Rayleigh-Plesset equation,opto-acoustic effect,Cavitation bubble,Au nanoparticles
更新于2025-09-19 17:13:59