Mechanism Of Laser Ablation Research Articles

Microscopic mechanism of ultrashort-pulse laser ablation of metals: a molecular dynamics study incorporating electronic entropy effects

The microscopic mechanism of metal ablation induced by ultrashort laser pulse irradiation is investigated. A two-temperature model scheme combined with molecular dynamics (TTM-MD) is developed to incorporate electronic entropy effects into the simulation of metal ablation while satisfying the energy conservation law. Simulation with the TTM-MD scheme reveals that ultrashort laser pulse irradiation near the ablation threshold causes high-energy atom/ion emission and sub-nanometer depth ablation, as observed experimentally, due to the electronic entropy effect. It is also shown that the electronic entropy effect is also significant in spallation.

Study on ablation behavior and mechanism of C/SiC composite irradiated by a laser with various parameters

AbstractC/SiC composite has been widely used as a high‐temperature material for engineering components due to its excellent thermal properties. Facing the rapid development and threat of high‐energy laser, study on the ablation resistance under laser irradiation is strongly required. In this work, a continuous high‐energy laser was applied to explore the laser ablation behavior and mechanism of C/SiC composite. From the results, C/SiC composite shows different morphologies when irradiated at various laser power densities for 500 and 700 W/cm2. We divided the ablation area into three regions; the central, transition, and edge regions, where the formation of SiO2, SiO, and the breakage of carbon fiber were observed. The generated highly reflective SiO2 layer reduces the absorption of laser energy, which is beneficial to lower the back‐surface temperature and reduce the damage of composite. In addition, we put forward the ablation physical models and ablation mechanisms irradiated at different power densities. The work provides a basis for the laser ablation resistance of C/SiC composites under different conditions.

Mechanism analysis of space debris removal by nanosecond pulsed laser

In this study, a numerical model is used to study the mechanism of laser ablation for space debris removal. The model couples the physical processes involved in laser ablation, including the heating, melting and evaporation of target (i.e. Aluminum), the formation of plume and plasma, and plasma shielding. Validation of the model is performed by comparing the simulated impulse density and impulse coupling coefficient with experimental data, showing the availability of the model in accurately describing the processes involved in laser ablation for removing space debris. The effects of laser irradiance, wavelength and pulse width on laser ablation were systematically studied by the model. In addition, the continuous laser ablation is explored and the effect of the laser pulse time interval is demonstrated. The results show that laser irradiation and pulse width have a significant impact on laser ablation, while the impact of wavelength is much smaller compared to the former two. In addition, using two short duration laser ablation instead of a long duration can significantly improve the impulse density obtained by the target and the corresponding impulse coupling coefficient, but the time interval between two laser pulses should not be too long.

Mathematical modeling of complex heat transfer in the context of the endovenous laser ablation

An initial-boundary value problem for quasi-linear model of complex heat exchange (where the conductive and radiative contributions are simultaneously taken into account), describing the mechanism of endovenous laser ablation, is studied. The existence and uniqueness of a solution is proved. An iterative procedure to find a solution is constructed and its convergence is established. The efficiency of the iterative procedure is illustrated by conducted numerical simulations.

Characterization of ablation conditions with the grayscale representation for Nd:YAG laser to decolor the blue‐ink on marble stone surface: Decoloration dependency on the laser flux power, wavelength, and the water spraying

AbstractAiming at artwork restoration application, to decolor the blue‐ink stained marble stone surface was studied for finding out efficient ablation conditions with the use of Q‐switched Nd:YAG laser as the function of laser flux power, wavelength, and its water spray effect. The blue ink mostly consists of indigo dye which absorbs light in the visible region. The decoloration, or decolor efficiency, was evaluated by using the grayscale representation instead of the RGB method. Our experimental results show that the 532 and 355 nm wavelengths are more suitable for blue‐ink decoloration. No decoloration was observed at the 1,064 nm ablation, which is usually regarded as effective on black‐crust stained surfaces. The decolor effect of the water‐sprayed surface was found to be effective at the higher laser flux power. A photo‐absorption‐assisted laser ablation mechanism is proposed in addition to the plasma‐assisted laser ablation mechanism.

Визуализационный анализ результатов континуально-атомистического моделирования кулоновского взрыва в металлах под влиянием ультракороткого (fs, ps) лазерного воздействия

A continuum-atomistic model that describes nonequilibrium thermal, hydrodynamic, and electronic processes in metals that occur under the action of ultrashort (fs, ps) laser radiation has been developed. A detailed study of two mechanisms of ultrashort laser ablation of Cu was carried out: fast - Coulomb, determined by Coulomb forces, and slow - thermal, realized in the unloading wave after the end of the laser pulse. Modeling showed that the excess nonequilibrium pressure of collectivized electrons plays a leading role in the formation of a strong electric field at the metal-vacuum interface. This effect can be taken as the basis for the Coulomb explosion in metals. The main feature of the work is the widespread use of modern visualization tools for processing and presenting simulation results.

Fundamental study of a femtosecond laser ablation mechanism in gold and the impact of the GHz repetition rate and number of pulses on ablation volume

In this work, we performed an experimental investigation supported by a theoretical analysis of single-shot laser ablation of gold to study the laser-matter interaction for predicting the ablation morphology and optimizing the process parameters. A set of coupled partial differential equations of the two-temperature model with dynamic optical properties and a phase explosion mechanism were used to determine the temporal and spatial evolution of the electron and lattice temperatures. The primary research focus of this work is to use the GHz frequency to investigate the ablation performance because the irradiated material is still far from thermal equilibrium during the laser-matter interaction. In contrast to conventional single-pulse laser ablation, intra-burst frequencies and the number of pulses are important factors in optimizing ablation efficiency and quality for fast material processing. Theoretical investigation revealed that the ablation volume increased due to heat accumulation, but the ablation quality decreased as the intra-burst frequencies decreased from 1000 GHz to 10 GHz. Moreover, the specific ablation volume increases with a higher burst number and lower intra-burst frequency at the expense of ablation quality.

Investigation of through micropatterns fabrication on C194 copper foil by ultraviolet nanosecond pulsed laser microdrilling

While the lead frames of C194 copper alloy widely used in IC packages contain high density of through micropatterns, the method for realizing high precision manufacturing of the micropatterns on copper foil with thickness down to a few hundred micrometers is highly demanded. In the present work, we demonstrate the feasibility of manufacturing high density through micropatterns on C194 copper foil with high precision and high uniformity by using ultraviolet nanosecond pulsed laser microdrilling. Specifically, the absorption coefficient of C194 copper foil for 355 nm wavelength is experimentally derived, based on which the sublimation enthalpy of the material is calibrated by iteratively comparing predicted crater morphology by finite element simulations with experimental data. Then the multi-pulse laser ablation mechanisms of C194 copper foil are investigated jointly by finite element simulations and experiments, which derive the quantitative correlation of ablation crater depth with laser ablation parameters. Finally, high density arrays of through micropatterns with high dimensional accuracy and high uniformity are fabricated on C194 copper foil with a thickness of 100 μm by the proposed ultraviolet nanosecond pulsed laser microdrilling with theoretically predicted repeat scanning number. Furthermore, the effect of pickling on surface quality and resistance of the manufactured copper lead frame is addressed. This work provides a feasible method for manufacturing copper alloy lead frames with high precision through micropatterns in an environmentally friendly manner.

Thermo-mechanical coupling induced Near-threshold double pulses femtosecond laser ablation enhancement in titanium

Near-threshold femtosecond laser surface treatment of titanium produces functional nanostructures, which has received much attention in applications and scientific researches. However, researches on the mechanism of near-threshold temporally-shaped femtosecond laser ablation of titanium are scarce, because the difficulty of investigating the modification mechanism of surface properties by sub-pulses below the ablation threshold. In this study, the double-pulse femtosecond laser ablation with various pulse separation was investigated. We found that the maximum ablation area appeared around 1 ps pulse separation at different fluences, and the ablation enhancement weakened with the increase of the fluence. The ultrafast pump–probe microscopy technique and ultrafast thermoelasticity model were used to investigate the mechanism. The result of pump–probe microscopy technique indicated that the enhancement of the area was caused by the decrease of transient reflectivity in the early stages which facilitated the subsequent sub-pulse energy absorption. The theoretical results indicate that the maximum ablation enhancement occurred at 1 ps, which is due to the combination of thermal and mechanical effects. The maximum of long axis diameter of periodic structure also appeared at 1 ps in multi-point processing. These findings have significant implications for the modulation of titanium surface nanostructures and providing theoretical support for processing.

Progress in Laser Ablation and Biological Synthesis Processes: “Top-Down” and “Bottom-Up” Approaches for the Green Synthesis of Au/Ag Nanoparticles

Because of their small size and large specific surface area, nanoparticles (NPs) have special properties that are different from bulk materials. In particular, Au/Ag NPs have been intensively studied for a long time, especially for biomedical applications. Thereafter, they played a significant role in the fields of biology, medical testing, optical imaging, energy and catalysis, MRI contrast agents, tumor diagnosis and treatment, environmental protection, and so on. When synthesizing Au/Ag NPs, the laser ablation and biosynthesis methods are very promising green processes. Therefore, this review focuses on the progress in the laser ablation and biological synthesis processes for Au/Ag NP generation, especially in their fabrication fundamentals and potential applications. First, the fundamentals of the laser ablation method are critically reviewed, including the laser ablation mechanism for Au/Ag NPs and the controlling of their size and shape during fabrication using laser ablation. Second, the fundamentals of the biological method are comprehensively discussed, involving the synthesis principle and the process of controlling the size and shape and preparing Au/Ag NPs using biological methods. Third, the applications in biology, tumor diagnosis and treatment, and other fields are reviewed to demonstrate the potential value of Au/Ag NPs. Finally, a discussion surrounding three aspects (similarity, individuality, and complementarity) of the two green synthesis processes is presented, and the necessary outlook, including the current limitations and challenges, is suggested, which provides a reference for the low-cost and sustainable production of Au/Ag NPs in the future.

Induction and amplification of elastic wave into cementitious material by applied laser ablation technique

To identify the elastic wave excitation behavior by means of laser pulse irradiation on cementitious material surface in this study, the application of pulsed laser irradiation system for laser ablation and spallation technique can be explained and proposed for a method for vibration (elastic wave) excitation used in NDT techniques. Expecting laser-induced-plasma-assisted ablation (LIPAA), laser ablation mechanism based on detecting AE (acoustic emission) signal is clarified as well as vibration amplitude and energy amplification by LIPAA with respect to such cementitious materials as cement paste. Elastic wave excitation into cementitious material due to laser ablation is not only influenced by pulse irradiation condition but also laser-induced-plasma-assisted ablation (LIPAA) process. The proposed technique for LIPAA works to induce and amplify the vibration (energy) generation when pulsed laser irradiation is implemented with predetermined fluence on cementitious material.

Investigation on Ablation Characteristics and Material Removal Mechanism of Si3N4 Ceramics by a New Type of Coupled Laser Beam

Due to the excellent comprehensive properties, Si3N4 ceramics have been widely studied and applied in the field of engineering structures. Conventional processing of Si3N4 ceramics faces a series of challenges, and laser processing has become an effective processing technology for hard and brittle materials. In this paper, a new type of dual-beam coupled nanosecond pulsed laser was used to carry out a series of ablation experiments on Si3N4 ceramic at various powers, and the laser ablation mechanism was analyzed. The equivalent diameter method and the equivalent area method were used to calculate the corresponding laser ablation threshold, and influence of laser power on surface roughness of the ablation hole edge, hole depth, removal volume and hole taper were explored. The results show that when the repetition frequency f = 10 kHz, wavelength λ = 532 nm and ablation time t = 6 s, the laser ablation thresholds of Si3N4 ceramic calculated by the equivalent diameter method and the equivalent area method are 0.55 J/cm2 and 0.59 J/cm2, respectively. In a certain power range, surface roughness of the ablation hole edge, hole depth and removal volume increase with the increase of laser power, while the ablation hole taper decreases with the increasing laser power. This innovative work is helpful to expand the scope of laser processing technology for hard and brittle materials, and has guiding significance for the optimization of laser processing technology parameters of Si3N4 ceramics.

Effect of laser pulse energy deposition method on nanosecond laser scanning ablation of SiCp/AA2024 composites

The control of the thermal stress and heat accumulation is major issue faced in the laser precision machining, and plays a key role in the laser machining of composite materials. In this pursuit, the present study envisaged the effect of pulse energy deposition method on the processing of particulate reinforced aluminum alloy matrix composites SiCp/AA2024. Specifically, by modulating the combination of the spot overlap ratio (SOR) and the area scanning passes, a variety of pulse energy deposition methods with the same number of received pulses per unit area were designed and applied on a target. The influence of the pulse energy deposition on processing was evaluated by measuring and comparing the ablation depth and surface roughness. The results showed that by using multiple scanning passes with small spot overlap ratios led to a good processing with a high ablation depth. Furthermore, the influence of SOR and scanning passes on the machining was studied using the control variable method. The influence of energy deposition method was studied from the aspect of nanosecond laser ablation mechanism, Fresnel reflection effect and heat accumulation.

Preparation of liquid metal circuits on flexible polymers by selective laser ablation: Essential mechanism of non-conductivity in ablation part

This work prepared liquid metal films by roll coating on various flexible substrates and then selectively ablated unwanted areas using near-infrared or ultraviolet lasers. The ablated regions lost their conductivity, while the remaining areas remained highly conductive, resulting in the successful fabrication of high-precision liquid metal circuits on various flexible and stretchable substrates. Mechanism of non-conductivity of liquid metal after laser ablation was investigated in detail. First, under the action of laser, most of Galinstan is evaporated. Second, although very small amounts of liquid metal still remain, they exist in the isolated state and cannot form continuous conductive paths. Finally, a continuous porous network material appears in the residue after laser ablation, which is the non-conductive oxidation products of metallic gallium, indium, and tin. Due to the above three reasons, the liquid metal film after laser ablation can realize the transition from conductive to non-conductive, and the patterning of the liquid metal can be achieved. The application of liquid metal circuits prepared by this method in wearable sensors (electronic skin) was explored. This study contributes to the mechanism of selective laser ablation to fabricate liquid metal circuits, promoting a better understanding of this method in the field of flexible electronics.

Laser Ablation Mechanism and Performance of Carbon Fiber-Reinforced Poly Aryl Ether Ketone (PAEK) Composites

The ablation mechanism and performance of carbon fiber (CF)-reinforced poly aryl ether ketone (PAEK) thermoplastic composites were studied in this paper. The results show that the ablation damaged area is controlled by the irradiation energy, while the mass loss rate is controlled by the irradiation power density. In the ablation center, the PAEK resin and CFs underwent decomposition and sublimation in an anaerobic environment. In the transition zone, the resin experienced decomposition and remelting in an aerobic environment, and massive char leaves were present in the cross section. In the heat-affected zone, only remelting of the resin was observed. The fusion and decomposition of the resin caused delamination and pores in the composites. Moreover, oxygen appeared crucial to the ablation morphology of CFs. In an aerobic environment, a regular cross section formed, while in an anaerobic environment, a cortex–core structure formed. The cortex–core structure of CF inside the ablation pit was caused by the inhomogeneity of fibers along the radial direction and the residual carbon layer generated by resin decomposition in an anoxic environment. The description of the ablation mechanism presented in this study broadens our understanding of damage evolution in thermoplastic composites subjected to high-energy CW laser irradiation.

Influence of Laser Process Parameters, Liquid Medium, and External Field on the Synthesis of Colloidal Metal Nanoparticles Using Pulsed Laser Ablation in Liquid: A Review.

Pulsed laser ablation in liquid, used for nanoparticle synthesis from solid bulk metal targets (a top-down approach), has been a hot topic of research in the past few decades. It is a highly efficient and ‘green’ fabrication method for producing pure, stable, non-toxic (ligand-free), colloidal nanoparticles, which is often challenging using traditional chemical methods. Due to the short time scale interaction between the laser pulses and the target, it is difficult to achieve complete control on the physical characteristics of metallic nanoparticles. Laser process parameters, liquid environment, and external fields vastly effect the shape and structure of nanoparticles for targeted applications. Past reviews on pulsed laser ablation have focused extensively on synthesising different materials using this technique but little attention has been given to explaining the dependency aspect of the process parameters in fine-tuning the nanoparticle characteristics. In this study, we reviewed the state of the art literature available on this technique, which can help the scientific community develop a comprehensive understanding with special insights into the laser ablation mechanism. We further examined the importance of these process parameters in improving the ablation rate and productivity and analysed the morphology, size distribution, and structure of the obtained nanoparticles. Finally, the challenges faced in nanoparticle research and prospects are presented.

Organic solvent assisted laser processing of transparent polymer films based on the swelling and penetration behavior

The laser processing of polymer films has significant importance due to the wide applications in various fields. The problems in laser processing of transparent polymer films caused by the poor absorption and current doping methods have prevailed. In this paper, a simple, efficient, and low-cost doping and laser processing method based on polymers’ swelling and penetration behavior was applied to improve the laser processing of transparent polymer films: organic solvent assisted laser processing (SALP). In the SALP method, various common organic solvent molecules (Ethanol, Acetone, N, N-dimethylformamide, Chloroform) were introduced into transparent polydimethylsiloxane (PDMS) films through the swelling and penetration (SP) pretreatment and acted as the dopant to improve the efficiency, capability, and quality of laser processing. Experimental results showed that the SALP method performed higher efficiency and capability (kerf depth: 296.79 ± 11.98 μm, kerf width: 16.59 ± 1.46 μm, kerf aspect ratio: 18.02 ± 1.98) under the same processing conditions compared to the typical laser processing (TLP) method (kerf depth: 137.36 ± 6.47 μm, kerf width: 27.30 ± 1.11 μm, kerf aspect ratio: 5.04 ± 0.31). The roughness of the kerf inner surface and the debris and microcracks on the kerf surface were also significantly reduced. More importantly, this method hardly influenced the original properties of the native polymer films due to the removability of organic solvents. On the one hand, the introduction of organic solvent molecules improved the optical absorption of PDMS films and the heat transfer during laser processing. On the other hand, the excitation, ionization, and dissociation of organic solvent molecules under laser irradiation improved the decomposition process of PDMS, which improved photochemical reaction and promoted the complete and uniform decomposition in laser processing. The SALP method has enlightening significance for improving the laser processing of polymers and investigating the laser ablation mechanism.

Laser ablation for material processing

The laser ablation is an established material processing for many applications in nanotechnology, materials science and biomedicine. The laser ablation can be carried out in vacuum, in air and in liquid. Laser ablation mechanisms and their products depend on laser fluence, wavelength, pulse duration, ablation environment as well as target composition, density, thickness, roughness. This contribution is addressed to laser ablation of solid targets with the aim of hot plasma generation and thin film deposition on substrates located in appropriate positions in vacuum and in air. In the first section is presented an example of forward and backward plasma accelerations using the sub-nanosecond laser at the PALS laboratory (Czech Republic) for pulsed laser deposition processing. In the second section is reported the use of a nanosecond laser coupled to a post-accelerating compact system employed at the INFN in Catania (Italy) to ablate germanium solid targets in vacuum and to deposit thin films on SiO2/Si substrates to modify their native features. The last section is focused on the use of the nanosecond laser at the Tandetron laboratory (Czech Republic) employed for pulsed laser deposition and laser-induced backward transfer processing in vacuum and in air.

Exploring Femtosecond Laser Ablation by Snapshot Ultrafast Imaging and Molecular Dynamics Simulation

Femtosecond laser ablation (FLA) has been playing a prominent role in precision fabrication of material because of its circumvention of thermal effect and extremely high spatial resolution. Molecular dynamics modeling, as a powerful tool to study the mechanism of femtosecond laser ablation, still lacks the connection between its simulation results and experimental observations at present. Here we combine a single-shot chirped spectral mapping ultrafast photography (CSMUP) technique in experiment and a three-dimensional two-temperature model-based molecular dynamics (3D TTM-MD) method in theory to jointly investigate the FLA process of bulky gold. Our experimental and simulated results show quite high consistency in time-resolved morphologic dynamics. According to the highly accurate simulations, the FLA process of gold at the high laser fluence is dominated by the phase explosion, which shows drastic vaporized cluster eruption and pressure dynamics, while the FLA process at the low laser fluence mainly results from the photomechanical spallation, which shows moderate temperature and pressure dynamics. This study reveals the ultrafast dynamics of gold with different ablation schemes, which has a guiding significance for the applications of FLA on various kinds of materials.

Laser Assisted Grinding of Rb-Sic Composites: Laser Ablation Behavior and Mechanism

Laser Assisted Grinding of Rb-Sic Composites: Laser Ablation Behavior and Mechanism