Pulsed Laser Ablation Of Aluminum Research Articles

Dynamic simulation on laser-metal interaction in laser ablation propulsion considering moving interface, finite thermal wave transfer, and phase explosion

Despite extensive investigations on the mechanism of laser-irradiated solid propellants, formulating an accurate model that characterizes more details of laser-target interactions remains a challenging task. In this paper, a thermal model for nanosecond pulsed laser ablation of aluminum was developed using the finite volume method which considers the instant recession on the propellant surface and the non-Fourier effect during heat conduction. The robust coupling iteration scheme adopted in the model tracks the dynamic boundary condition due to instant propellant removal. In particular, the pre-qualified threshold is used as discriminator for phase explosion and the thermal relaxation time is introduced to quantify the non-Fourier effect on heat conduction. In addition, the temperature-dependent physical and optical parameters of the propellant were also regarded in the proposed model. The numerical implementations for Gaussian laser ablation of aluminum were performed at different laser fluences and thermal relaxation times. The theoretical computation of the ablation depth coincides well with the experimental results to validate the feasibility of the model.

Spatial restriction on properties of nanosecond pulsed laser ablation of aluminum in water

The evolution of plasma radiation, shock waves and the bubbles generated by laser ablation in liquids (LAL) has been investigated in spatial restriction conditions by the temporally resolved plasma radiation images and time-resolved laser shadowgraphy. No significant plasma enhancement effect is observed at the moments when two reflected waves converge in opposite directions. Two reasons may account for this phenomenon: one is that cavitation bubbles block the interaction between reflected waves and plasma, which prevents reflected waves from transmitting energy to the plasma; and the other is that the laser energy is significantly absorbed by the water medium and the emission of plasma decays rapidly in water. The results indicate that the plasma luminous intensity attenuates and lifetime decreases under restricted conditions, which is due to the existence of the moving breakdown model in the water. The Bjerknes effect of the wall on the bubbles leads to the asymmetry of the bubble evolution under restricted conditions. The dynamics of the first bubble generated by LAL is described in an analytic method with the Rayleigh–Plesset equation. The results further indicate Bjerknes force exerts little impact upon bubble evolution in the extension phase, but imposes huge effects at the shrinkage phase.

A simple finite element model to study the effect of plasma plume expansion on the nanosecond pulsed laser ablation of aluminum

In this paper, a simple model was proposed using finite element analysis (FEA) with a commercial FEA software ABAQUS to simulate the two-dimensional (2-D) laser heat transfer in an aluminum material. Without relying on the conventional hydrodynamic model, the proposed model not only predicts the evolutions of the temperature field and ablation profiles in the target material, but also provides an estimation on the evolutions of electron density, plasma temperature, and plasma absorption coefficient. The assumptions used in the model include the local thermal equilibrium and additional assumptions regarding the average plasma temperature and vapor density. The assumptions allowed the laser heat transfer equation to be solved together with the Saha–Eggert equation and conservation equations of matter and charge. When compared to the existing hydrodynamic models, the proposed model solves a less number of nonlinear equations and hence is computationally more efficient. The proposed FE model was employed to study the plasma-shielding effect on PLA produced by a 193 nm Excimer laser and a 266 nm Nd:YAG laser. The predictions of ablation depths, electron density, and plasma temperature agree well with the experimental data. Moreover, effects of the laser intensity and the average plasma temperature on the efficiency of the plasma shielding during PLA were also investigated and discussed in this study.

Enhancement of ablation rate and production of colloidal nanoparticles by irradiation of metals with nanosecond pulsed laser in presence of external electric field

This paper presents the results of experimental study on the effect of electric field on the ablation rate during the nanosecond pulsed laser ablation of aluminum and copper in deionized water. The effect of electric field strength on the material removal rate and its mechanisms were investigated both in the electric field parallel and perpendicular to the laser beam path schemes. The ablation rate was estimated by measuring the dimensions of craters on the target induced by laser. The crater dimensions and optical properties of the produced colloidal nanoparticles were characterized by means of optical microscopy and UV–Vis absorption spectroscopy, respectively. The results indicate that pulsed laser ablation in the presence of an electric field significantly leads to higher material removal rate. The experimental results also confirm that the crater geometry extremely depends on the direction of the electric field with respect to the laser beam direction. The UV–Vis spectra show that the nanoparticles production efficiency increases with increasing the electric field strength.

Modeling of pulsed laser ablation of aluminum under the action of infrared nanosecond laser pulses

The paper presents the results of numerical simulation of aluminum ablation process that is caused by a series of incident nanosecond pulses on a wavelength λ=1064 nm. The mechanism of normal evaporation and the effect of plasma shielding were taken into account. As a result of mathematical modeling the ablation depth was obtained. It is shown that plasma shielding reduces the effectiveness of ablation process much more than cooling of the aluminum surface between pulses.

Uncertainty quantification for modeling pulsed laser ablation of aluminum considering uncertainty in the temperature-dependent absorption coefficient

In this paper, an extension of the result of Wang et al. (“Modeling pulsed laser ablation of aluminum with finite element analysis considering material moving front,” Int. J. Heat & Mass Transfer, 113, 1246–1253, 2017) concerning the problem of uncertainty quantification for pulsed laser ablation (PLA) of aluminum is considered, when the source of uncertainty is due to an inherent randomness of the temperature-dependent absorption coefficient. In particular, we use a generalized polynomial chaos (gPC) method to incorporate the parameter uncertainty for the temperature-dependent absorption coefficient within the representation of the laser heat conduction phenomena. Furthermore, numerical simulation studies for the PLA of aluminum, with nanosecond Nd:YAG 266 nm pulsed laser, that demonstrate the proposed gPC predictions are presented. Finally, a sensitivity study is performed to identify whether small changes in the lower and/or upper parameter values of the absorption coefficient provide the most variance in the thermal and ablation responses.

A thermal model for nanosecond pulsed laser ablation of aluminum

In order to simulate the nanosecond pulsed laser ablation of aluminum, a novel model was presented for the target ablation and plume expansion. The simulation of the target ablation was based on one-dimensional heat conduction, taking into account temperature dependent material properties, phase transition, dielectric transition and phase explosion. While the simulation of the plume expansion was based on one-dimensional gas-dynamical equation, taking into account ionization, plume absorption and shielding. By coupling the calculations of the target ablation and plume expansion, the characteristics of the target and plume were obtained. And the calculated results were in good agreement with the experimental data, in terms of ablation threshold and depth within the fluence range of the tested laser. Subsequently, investigations were carried out to analyze the mechanisms of nanosecond pulsed laser ablation. The calculated results showed that the maximum surface temperature remained at about 90% of the critical temperature (0.9Tc) due to phase explosion. Moreover, the plume shielding has significant effects on the laser ablation, and the plume shielding proportion increase as the laser fluence increasing. The ambient pressure belows 100 Pa is more suitable for laser ablation, which can obtained larger ablation depth.

Modeling pulsed laser ablation of aluminum with finite element analysis considering material moving front

During the pulsed laser ablation (PLA) of solid materials, the surface of the target material progressively recedes which in turn necessitates to account for the moving front boundary in the formulation of the laser heat conduction problem. Hence, developing an accurate predictive simulation model that captures the material moving front and updates simultaneously the laser source boundary conditions is an important and yet challenging task. In this paper, the PLA of aluminum is formulated and modeled with finite element analysis (FEA) that considers the instant material removal during the ablation process. Here, the implementation of such an FEA enables a strong coupling between the progressive surface recession (i.e., the shape change of the target material) and the laser heat conduction. Moreover, the proposed numerical simulation model not only predicts the progressive surface recession due to the material evaporation in the low laser fluence regime, but it also captures the ablation depth due to the material phase explosion in the high laser fluence regime. In addition, the temperature-dependent material and optical properties of the aluminum target are considered in the simulation. With nanosecond Nd:YAG 266 and 193nm laser pulses, simulations are performed for the PLA of aluminum under various laser fluence. The predicted ablation depths under low laser fluence clearly show better agreement with experimental data, when compared to other predictions based on the hydrodynamics simulation model. Furthermore, the predicted threshold of the material phase transition in the high laser fluence regime also shows a good degree of consistency with experimental data.

INVITED] Control of femtosecond pulsed laser ablation and deposition by temporal pulse shaping

This study explores the effects of temporal laser pulse shaping on femtosecond pulsed laser deposition (PLD). The potential of laser pulses temporally tailored on ultrafast time scales is used to control the expansion and the excitation degree of ablation products including atomic species and nanoparticles. The ablation plume generated by temporally shaped femtosecond pulsed laser ablation of aluminum and graphite targets is studied by in situ optical diagnostic methods. Taking advantage of automated pulse shaping techniques, an adaptive procedure based on spectroscopic feedback regulates the irradiance for the enhancement of typical plasma features.Thin films elaborated by unshaped femtosecond laser pulses and by optimized sequence indicate that the nanoparticles generation efficiency is strongly influenced by the temporal shaping of the laser irradiation. The ablation processes leading either to the generation of the nanoparticles either to the formation of plasma can be favored by using a temporal shaping of the laser pulse. Insights are given on the possibility to control the quantity of the nanoparticles.The temporal laser pulse shaping is shown also to strongly modify the laser-induced plasma contents and kinetics for graphite ablation. Temporal pulse shaping proves its capability to reduce the number of slow radicals while increasing the proportion of monomers, with the addition of ionized species in front of the plume. This modification of the composition and kinetics of plumes in graphite ablation using temporal laser pulse shaping is discussed in terms of modification of the structural properties of deposited Diamond-Like Carbon films (DLC). This gives rise to a better understanding of the growth processes involved in femtosecond-PLD and picosecond-PLD of DLC suggesting the importance of neutral C atoms, which are responsible for the subplantation process.

Synthesis of aluminum oxide nanoparticles using laser ablation in liquid

AbstractWe report the photoluminescence (PL) properties of aluminum oxide nanoparticles synthesized in a liquid confined ambient using pulsed laser ablation of aluminum. The colloidal suspension was dried on a quartz substrate using an IR heat lamp prior to further structural and optical characterization. TEM measurement confirms the particles of nano dimension with average size of ∼23 nm and of spherical shape. XRD measurement shows a strong peak at 31.5° indicating the presence of aluminum oxide. The PL measurement using xenon lamp as excitation source shows a broad peak. The PL peak position shifts towards longer wavelength as the excita‐ tion wavelength is changed to longer wavelengths. The shift may be due to presence of intermediate compounds like Al2O in addition to Al2O3. The appearance of luminescence bands may be associated with the defects formed in the non‐equilibrium phases and the oxygen vacancy defects which are specific features of the nanostructured state in nanostructures formed during the laser ablation inside the liquid confined ambient. A comparative study of laser ablated aluminum plasma in air and water to elucidate the various processes is also presented. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Ion Kinetic Energy Distributions and Mechanisms of Pulsed Laser Ablation on Al

A detailed investigation on the ion kinetic energy distributions of ions ejected in the nanosecond pulsed laser ablation of aluminum is reported. For laser fluences just over threshold, the emerging ions fit shifted neat Maxwell−Boltzmann-Coulomb (MBC) distributions. For fluences higher than ∼1.3 J/cm2, the Al+ distributions split into two MBC contributions peaked at different energies. It is demonstrated that the observed Al+ ion distribution has two components, one fast, correlated with the direct multiphoton laser ionization, and the other slow, associated with electron−Al0 collisions in the solid. A similar behavior is observed at higher fluences for all Al ion distributions indicating that the electron-impact ionization of Al rate constants is faster than that of recombination and other possible collision channels. In addition, the linear relationship between the Coulomb velocities and the ion charges and the behavior of Coulomb energy of the ions versus the laser fluence suggest the appearance of an...

Anisotropic emission in laser-produced aluminum plasma in ambient nitrogen

We report on the dynamical expansion of pulsed laser ablation of aluminum in ambient pressure of nitrogen using images of the expanding plasma. The plasma follows shock model at pressures of 0.1 Torr and drag model at 70 Torr, respectively, with incident laser energy of 265 mJ. The plasma expansion shows unstable boundaries at 70 Torr and is attributed to Rayleigh–Taylor instability. The growth time of Rayleigh–Taylor instability is estimated between 0.09 and 4 μs when the pressure is varied from 1 to 70 Torr. The pressure gradients at the plasma–gas interface gives rise to self-generated magnetic field and is estimated to be 26 kG at 1 Torr ambient pressure using the image of the expanding plasma near the focal spot. The varying degree of polarization of Al III transition 4s 2S 1/2–4p 2P° 3/2 at 569.6 nm gives rise to anisotropic emission and is attributed to the self-generated magnetic field that results in the splitting of the energy levels and subsequent recombination of plasma leading to the population imbalance.

Reactive pulsed laser ablation: Plasma studies

We report on the pulsed laser ablation of aluminum (Al) plasma in presence of ambient nitrogen to understand the formation of aluminum nitride (AlN). Formation of carbon nitride (CN) and titanium oxide (TiO) by pulsed laser-ablation of graphite and titanium targets in presence of ambient nitrogen and oxygen is also compared. We discuss the dynamics of plasma expansion based on existing models, shock and drag models, and the plasma gas interface distortion, Rayleigh-Taylor instability at various ambient pressures of nitrogen. Since Rayleigh-Taylor instability may give rise to self-generated magnetic field in the plasma, an attempt is made to understand the mechanism of generation as well as the estimation of this field near the focal spot using the information from the images of the expanding plasma. This is the first time images of the expanding plume are used to estimate self generated magnetic fields. At the irradiance level used in the experiment the field is high very close to the target surface therefore we expect splitting of the energy levels thus giving rise to emissions that may be anisotropic in nature. We discuss the extent of anisotropy by measuring the degree of polarization using emission intensity in optical emission spectrum of selected Al III transition 4s2S1/2–4p2P3/2oat 569.6 nm using both nanosecond and picosecond pulses.

Characterization of laser-produced aluminum plasma in ambient atmosphere of nitrogen using fast photography

We report on the pulsed-laser ablation of aluminum in ambient pressure of nitrogen varying from 0.01 to 70 Torr using images of the expanding plasma plume. At pressures ⩾1 Torr plasma–gas interface showed severe distortion in the front of the expanding plume. The plasma expansion velocity showed oscillatory behavior with delay time beyond 260 ns and is attributed to Rayleigh–Taylor instability. The effect of background gas on inducing polarization in the ablated plasma is also reported. At low pressure of 0.1 Torr the degree of polarization of Al III transition 4s 2S1/2–4p 2P3/20 at 569.6 nm increased with delay time. At pressures ⩾1 Torr it showed an oscillatory behavior. The observed steep pressure gradient at the plasma–gas interface may result in strong self-generated magnetic field due to Rayleigh–Taylor instability.

Pulsed laser ablation of aluminum in the presence of nitrogen: Formation of aluminum nitride

We report on the pulsed laser ablation of aluminum in the presence of nitrogen gas using a 1.06 μm wavelength of Nd:YAG laser. A prominent band of aluminum nitride corresponding to the (0-0) band of the system belonging to a π3−π3 transition was observed at 507.8 nm. An attempt is made to identify the ionized states of aluminum and nitrogen contributing to formation of the AlN band. AlN films were deposited at room temperature and characterized using x-ray diffraction. A direct correlation between the laser ablated aluminum plasma and the deposited AlN film is reported.

Study on the Interaction between the Laser-Ablated Aluminum Plume and the Nitrogen Discharge Plasma by Time- and Space-Resolved Spectroscopy

Pulsed discharge of nitrogen was shown to be a very effective means to generate atomic nitrogen whose reactivity favored the synthesis of nitrides. In order to form aluminum nitride, such a plasma was allowed to interact with the plume generated by pulsed-laser ablation of aluminum. The plasma reaction was studied by time- and space-resolved optical emission spectroscopy. Emissions from ionic species of nitrogen (N+ and N2+) in the reaction region were observed. They were believed to be excited by the shock front generated by the pulsed-laser ablation. The delay time between ablation and discharge could be tuned to maximize the N+ emission. That condition also produced the purest aluminum nitride powders.