Laser Induced Plasma Expansion Research Articles

N-waves propagating through the Mars atmosphere

One of the particular interest of the SuperCam microphone onboard the NASA’s Perseverance rover is that it is coupled with its own reproducible sound source, the blast waves generated by the SuperCam laser-induced plasma expansion. This unique emission-reception pair on Mars is used to investigate the propagation of spark-induced N-waves through the turbulent CO2-dominated Mars atmosphere. The analysis of waveforms shows large distortions over a burst of 30 subsequent shots, which is consistent with previous laboratory recordings of N-waves through thermal turbulence. Especially, this distortion leads to a scattering of the peak pressure amplitude, whose distribution can be fitted with a generalized gamma function. For bursts recorded farther than 4 m, the distribution gets asymmetric with a shift of the maximum toward the left of the median due to peaks amplified more than twice the median amplitude, likely due to caustics that randomly focus the acoustic wave. On the other hand, over a Martian year, the absolute peak pressure varies by ∼50% due to changes in the acoustic impedance and Rankine-Hugoniot conditions, due to the seasonal cycles of pressure and temperature at the surface of Mars.

Pliable solid medium as a plasma confinement layer for laser peening

Laser peening is a promising surface treatment technique for enhancing the mechanical performance of metals. In laser peening, the plasma confinement layer contributes to the generation of high-pressure shockwaves by suppressing the expansion of laser-induced plasma. Therefore, the choice of a plasma confinement layer is important for improving laser peening effectiveness. For laser peening in environments where liquid materials cannot be used as a plasma confinement layer, alginate gel, which is a pliable material with shape-following capabilities, has been proposed to reduce the acoustic impedance mismatch caused by surface roughness when using solid materials. In this study, the feasibility of alginate gel as a plasma confinement layer and an appropriate process window for laser irradiation were investigated. The results of this study are then presented.

Comparative study of pulsed laser-induced breakdown at a metal-liquid interface at two liquid temperatures using a beam-deflection probe

A pulsed Nd: YAG laser is tightly focussed on a nickel wire-shaped target immersed in a glass cell filled with distilled de-ionized water. The resultant shock wave and cavitation bubble dynamics, occurring because of the laser-induced plasma expansion, are recorded using a pump-probe set-up. The shock wave and cavitation bubble dynamics are recorded at two temperatures of the liquid. It was observed that a higher liquid temperature results in a higher velocity of shock wave propagation, which consequently led to a higher pressure exerted by the shock wave. The experimentally determined shock wave velocities were 1.8 and 1.9 km/s for cold and hot water, respectively. Consequently, the pressure values amounted to 0.23 and 0.27 GPa, respectively. Cavitation bubble radii determined experimentally were 975 μm and 742 μm, for cold and hot water, respectively. Also, a higher liquid temperature led to a higher order of cavitation bubble formation.

Time-Resolved Imaging of Femtosecond Laser-Induced Plasma Expansion in a Nitrogen Microjet

We report on the study of ultrafast laser-induced plasma expansion dynamics in a gas microjet. To this purpose, we focused femtosecond laser pulses on a nitrogen jet produced through a homemade De Laval micronozzle. The laser excitation led to plasma generation with a characteristic spectral line emission at 391 nm. By following the emitted signal with a detection system based on an intensified charge-coupled device (ICCD) we captured the two-dimensional spatial evolution of the photo-excited nitrogen ions with a temporal resolution on the nanosecond time scale. We fabricated the micronozzle on a fused silica substrate by femtosecond laser micromachining. This technique enabled high accuracy and three-dimensional capabilities, thus, providing an ideal platform for developing glass-based microfluidic structures for application to plasma physics and ultrafast spectroscopy.

Influence of grain size on dynamic characterizations of laser-driven grain ejection

When intense laser pulse irradiates a target surface, the energetic processes of generation and expansion of laser-induced plasma will affect a localized pressure impulse around the irradiation zone. As a result, pulsed laser ablating granular target can drive a physical phenomenon of grain ejection. In this work, taking dry glass beads with different grain sizes as an example of granular targets and using high-speed video camera, we experimentally investigate the grain-size dependent dynamics of grain ejection driven by nanosecond laser pulses. The measured video sequences clearly exhibit that the laser-driven grain ejection process can be separated into two regimes: early-stage fast ejecting process and later-stage slow ejecting process. We find that there exists an obvious grain size effect on the kinetic energy of grains in the early-stage ejecting process. In addition, the temporal evolution of transient ejection of a curtain diameter <inline-formula><tex-math id="M6">\begin{document}$ D\left(t\right) $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20220243_M6.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20220243_M6.png"/></alternatives></inline-formula> corresponding to the later-stage ejecting process obeys the well-known “point source” law, <inline-formula><tex-math id="M7">\begin{document}$ {D\left(t\right)=\alpha t}^{\beta } $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20220243_M7.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20220243_M7.png"/></alternatives></inline-formula>, where both parameters <inline-formula><tex-math id="M8">\begin{document}$ \alpha $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20220243_M8.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20220243_M8.png"/></alternatives></inline-formula> and <inline-formula><tex-math id="M9">\begin{document}$ \beta $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20220243_M9.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="14-20220243_M9.png"/></alternatives></inline-formula> depend on grain size. The observations mentioned above can be reasonably explained by considering the grain size dependent efficiency of impulse coupling between grain and plasma flow and plasma features generated by interaction of laser pulse with granular targets. These experimental results improve the understanding of the mechanism of laser-driven grain ejection.

Characteristics of laser-induced plasma under reduced background pressure with Doppler spectroscopy of excited atomic species near the shockwave front

We present measurements of Laser Induced Plasma expansion relying on classical, laterally resolved spectroscopy. Easy observable Doppler splitting of Cu I 324.75 nm spectral line provides measurement of radial expansion velocity in a straightforward way. The measurements are conducted in atmosphere of air, argon and hydrogen at low pressure in the range 20–200 Pa. We found that expansion velocity is linearly decreasing if pressure of surrounding gas increases, with velocity/pressure slope nearly the same for all three gases. Copper atoms have the highest expansion speed in argon ( ∼ 50 km/s) and the smallest speed in air ( ∼ 42 km/s). It is found that expansion velocity increases linearly with irradiance, while intensity of the spectral line is quite insensitive to the laser irradiance.

Laser induced plasma expansion and existence of local thermodynamic equilibrium

In this paper we present a simple model of the laser induced plasma (LIP) expansion in a low pressure surrounding atmosphere. The model is based on assumption that expansion process is dominantly governed by kinematics of the heavy particles. The model is accompanied with a simple, yet effective, Monte-Carlo simulation. Results of the simulation are compared with spectroscopic measurements of the laser induced copper plasma expanding in low pressure (200Pa) hydrogen atmosphere. We found that characteristic expansion time of the LIP is proportional to the linear dimension of the initial volume heated up by the laser. For sufficiently large initial volume copper plasma remains in local thermodynamic equilibrium on the submicrosecond-microsecond scale. It is shown that diagnostics based on the spectral lines of the hydrogen atmosphere is not suitable for characterization of the core of the copper plasma. We have demonstrated importance of radially resolved spectroscopic measurements as a key step for correct diagnostics and understanding of laser induced plasma.

Generation and expansion of laser-induced plasma as a spectroscopic emission source

Laser-induced plasma represents today a widespread spectroscopic emission source. It can be easily generated using compact and reliable nanosecond pulsed laser on a large variety of materials. Its application for spectrochemical analysis for example with laser-induced breakdown spectroscopy (LIBS) has become so popular that one tends to forget the complex physical and chemical processes leading to its generation and governing its evolution. The purpose of this review article is to summarize the backgrounds necessary to understand and describe the laser-induced plasma from its generation to its expansion into the ambient gas. The objective is not to go into the details of each process; there are numerous specialized papers and books for that in the literature. The goal here is to gather in a same paper the essential understanding elements needed to describe laser-induced plasma as results from a complex process. These elements can be dispersed in several related but independent fields such as laser-matter interaction, laser ablation of material, optical and thermodynamic properties of hot and ionized gas, or plasma propagation in a background gas. We believe that presenting the ensemble of understanding elements of laser-induced plasma in a comprehensive way and in limited pages of this paper will be helpful for further development and optimized use of the LIBS technique. Experimental results obtained in our laboratory are used to illustrate the studied physical processes each time such illustration becomes possible and helpful.

Ultraviolet versus infrared: Effects of ablation laser wavelength on the expansion of laser-induced plasma into one-atmosphere argon gas

Laser-induced plasma from an aluminum target in one-atmosphere argon background has been investigated with ablation using nanosecond ultraviolet (UV: 355 nm) or infrared (IR: 1064 nm) laser pulses. Time- and space-resolved emission spectroscopy was used as a diagnostics tool to have access to the plasma parameters during its propagation into the background, such as optical emission intensity, electron density, and temperature. The specific feature of nanosecond laser ablation is that the pulse duration is significantly longer than the initiation time of the plasma. Laser-supported absorption wave due to post-ablation absorption of the laser radiation by the vapor plume and the shocked background gas plays a dominant role in the propagation and subsequently the behavior of the plasma. We demonstrate that the difference in absorption rate between UV and IR radiations leads to different propagation behaviors of the plasma produced with these radiations. The consequence is that higher electron density and temperature are observed for UV ablation. While for IR ablation, the plasma is found with lower electron density and temperature in a larger and more homogenous axial profile. The difference is also that for UV ablation, the background gas is principally evacuated by the expansion of the vapor plume as predicted by the standard piston model. While for IR ablation, the background gas is effectively mixed to the ejected vapor at least hundreds of nanoseconds after the initiation of the plasma. Our observations suggest a description by laser-supported combustion wave for the propagation of the plasma produced by UV laser, while that by laser-supported detonation wave for the propagation of the plasma produced by IR laser. Finally, practical consequences of specific expansion behavior for UV or IR ablation are discussed in terms of analytical performance promised by corresponding plasmas for application with laser-induced breakdown spectroscopy.

Modeling of laser induced plasma expansion in the presence of non-Maxwellian electrons

The one-dimensional expansion into vacuum of ion-electron plasma produced by laser ablation is investigated. The ions considered as an ideal fluid are governed by a fluid model where charge quasineutrality is assumed to prevail, while electron density follows a non-Maxwellian distribution. Showing that the expansion can be described by a self-similar solution, the resulting nonlinear Euler equations are solved numerically. It is found that the deviation of the electrons from Maxwellian distribution gives rise to new asymptotic solutions of physical interest affecting the density and velocity of plasma expansion.

The role of continuum radiation in laser induced plasma spectroscopy

This paper focuses on the interpretation of the origin of the continuum radiation in Laser Induced Plasma (LIP) emission spectra, a subject that has received little consideration in the literature when compared to the analysis of the line emission spectrum. The understanding of the spectral peculiarities observed immediately after the laser pulse, when the continuum radiation prevails on discrete emission lines, can be extremely important to retrieve the initial conditions of LIP and to correlate the produced plasma to the ablation mechanism. In this work, in addition to a qualitative interpretation of the LIP continuum in the initial stage of expansion, a methodology is proposed for a better measurement of the atomic temperature in the expansion stage of the LIP. Such methodology is based on the analysis of the combined Boltzmann and Planck plots. The results obtained stress once again the importance of considering non equilibrium effects in the initial stage of LIP expansion.

Kinetic model of titanium laser induced plasma expansion in nitrogen environment

A theoretical model to investigate the laser induced plasma (LIP) produced by a nanosecond laser pulse interacting with a metallic titanium target in a nitrogen environment is presented. In this work the influence of chemical processes on the plume expansion has been investigated, applying a 2D fluid dynamic code under local thermodynamic equilibrium or chemical non-equilibrium approximations.

The flip-over effect in self-similar laser-induced plasma expansion

We present a rigorous study of a dynamical model for a nonsymmetric expansion of laser-induced plasma plumes into the vacuum. The model is used in the laser film deposition technique and for remote chemical analysis in the so-called laser-induced breakdown spectroscopy. It defines a particular class of solutions of the hydrodynamics equations when the (plasma) mass density, pressure, and temperature as functions of position have level surfaces that are ellipsoids. The time evolution of ellipsoid semiaxes is determined by the dynamical model. In this model we investigate the flip-over effect: A pancakelike shape of the plasma plume turns into a cigarlike shape and vice versa in due course of its expansion. The effect has been observed in experiments as well as in numerical simulations. In many practical cases, axially symmetric plasma plumes with the adiabatic constant of 53 (ideal gas) are used. For this case we prove that the flip-over effect occurs exactly once in the above dynamical model. This rigorous result agrees with the earlier experimental and numerical evidence and, hence, validates a wide applicability of the model.

Modeling Laser-Induced Plasma Expansion Under Equilibrium Conditions

A theoretical investigation of the expansion of the plasma, produced by a nanosecond laser pulse hitting a titanium metallic target, has been carried out. The study is oriented to understand the interaction of the plasma plume with the surrounding gas (air) not only from the fluid dynamic point of view, but also considering the effects of chemical reactions. To this purpose, a 2-D solver of the Euler equations has been developed and self-consistently coupled with the local thermodynamic equilibrium calculation. The results show the plasma confinement due to the ambient gas and the appearance of metallic oxides in proximity of the plume border.

Selective removal of 10–40-nm particles from silicon wafers using laser-induced plasma shockwaves

Current and projected nanoparticle cleaning requirements, especially in semiconductor and nano-manufacturing, necessitate a technique that is not only capable of removing sub-100 nm particles, but also is damage-free and able to perform localized (selective) area cleaning of a relatively small number of particles. A particle cleaning technique based on laser-induced plasma (LIP) shockwaves has been considered and investigated in recent years as a prospective approach. In the current study, the removal of polystyrene latex (PSL) nanoparticles in the diameter range of 10–40 nm from silicon substrates is demonstrated using shockwaves generated by the expansion of LIP for the first time. The effectiveness and practical uses of the LIP technique in the sub-100-nm range are also discussed.

A combined fluid dynamic and chemical model to investigate the laser induced plasma expansion

In this paper a theoretical model to study the time and space evolution of the plasma generated during the interaction between a KrF laser and a Ti surface has been developed. An optimisation of the initial parameters in the continuous evaporation approximation, such as temperature (T0), rate production of matter (zd), velocity (v0) and ionization degree (α), has been carried out to reproduce the experimental profiles obtained by time and space resolved laser induced plasma spectroscopy. The best initial conditions have been found by “Downhill simplex” method and their effects on the plasma evolution have been discussed.

Non-equilibrium conditions during a laser induced plasma expansion

A theoretical model to simulate the laser induced plasma (LIP) expansion with chemical kinetics has been developed for a Ti target. Our attention has been also focused on the influence of initial conditions on the plume expansion. In particular, changing the initial speed, temperature, pressure and plume extension, the speed of expansion and the width of the time of flight (TOF) peak change. A systematic study of the effect of all these parameters on the plume expansion can lead to a method that allows the determination of initial conditions of the expansion, which are not available experimentally because of the delay necessary to trigger the measure apparatus with the laser pulse.

Modeling of gas dynamics for a laser-generated plasma: propagation into low-pressure gases

The physical phenomena involved during three-dimensional axisymmetric laser-induced plasma expansion into background gas are numerically studied. For this purpose, a multispecies hydrodynamic model is developed which considers the effects of mass and ambipolar diffusions, thermal conduction, viscosity, and nonequilibrium conditions for ionization. This model is applied to describe quantitatively the Si plasma plume expansion into Ar or He gases. It is shown that the mechanism of plasma expansion depends critically on both the pressure and mass of the background gas. The shock front expansion is found to be strongly correlated with ion dynamics. A pronounced difference between heavy-particle and electron temperatures indicates a persistent lack of equilibrium between the heavy particle and the electron in the plasma plume expansion. The Si atoms of the rarefied plume are essentially driven by the backward-moving background gas as a result of a mass diffusion process. It is also noted that the diffusion processes are only important in the last expansion stage, and are less significant in the first stage. Therefore, it is shown that a computation which does not include diffusion effects (Euler equations) can adequately describe only the earliest stage of plasma expansion into background gas. The ability of the Navier-Stokes hydrodynamic multispecies model to predict the key role of the background gas type (Ar, He) and pressure is demonstrated.

Optical spectroscopy of emission from Si—SiOx nanoclusters formed by laser ablation

This paper reports an experimental study of optical emission from Si—SiOx nanoclusters in a laser-induced plasma plume produced by conventional laser ablation techniques. Emission spectroscopy and optical time-of-flight measurements (TOF) were carried out during reactive ablation of Si targets in He, Ar or O2 atmosphere. Several broad emission bands detected and identified as emission from Si nanoclusters formed at early stage of laser induced plasma expansion. The bands observed show a good spectral correlation with photoluminescence bands of Si—SiOx nanoclusters thin films and Si nanoclusters absorption bands. Analysis of plume dynamics showed considerably slower translational velocities and broader energy distribution of nanoparticles than those of neutrals and ions. From TOF measurements large spectral band widths can be explained by superposition of radiation from the clusters of different size. Two fluxes of clusters, forward and reversed, found within the plasma plume. Their spatial behavior and pressure dependence can be explained by the character of their motion, which is determined by complex hydrodynamics of plume expansion.

2d Modeling of Laser Induced Plasma Expansion

ABSTRACTAn axisymmetric two-dimensional modeling of plasma expansion in background gas is carried out to provide a better understanding of pulsed laser deposition (PLD) processes. This model takes into account the plasma plume dynamics just after the laser ablation pulse. It is shown that hydrodynamic behaviour and thermal relaxation of the plasma are strongly dependent on the nature and the pressure of background gas. In good agreement with experimental results backward movement of particles is clearly identified at a late expansion stage (≥ 2 μs).