Expansion Of Laser-produced Plasma Research Articles

The wide spectral range characteristics and dynamic evolution of laser-produced tin plasmas

The energy levels and transitions of highly charged Sn ions are key data for analyzing emission spectra, radiative opacity, and conversion efficiency of laser-produced Sn plasmas. Temporally–resolved spectra in the 6–45-nm range were acquired via high-precision, spatio–temporally resolved techniques. In addition, the Cowan code, based on Hartree–Fock multi-configurational interactions, was used to perform structural calculations for Sn4+–Sn13+ ion spectra. Emission spectra in the 11–18-nm range were primarily attributed to Sn8+–Sn12+ ions, with transitions involving principal quantum numbers Δn=0 and Δn=1. Whereas, emission spectra in the 6–11-nm and 18–45-nm ranges were mainly attributed to Sn9+–Sn13+and Sn4+– Sn9+ions, with transitions involving principal quantum numbers Δn=1,2. Furthermore, Segmented simulations were conducted based on the assumptions of a normalized Boltzmann distribution among the excited states and a steady-state collisional-radiative model to explain the characteristics of the radiation spectra and variations in state parameters variations during laser-produced plasma expansion from the core to the outer periphery. A specific analysis was conducted on the temporal evolution of the electron temperature and density, while the charge state of the plasma was analyzed over the 6–18-nm range. Based on the spectral diagnostics, this work focused on the impact of non-uniformity in the expansion of the Sn plasma.

Geometrical Analysis of the Stagnation Zone in Laterally Colliding Plasmas: Effects of Plasma Plume Separation and Ablating Target Material

The influence of an ablating target’s atomic mass on the development and growth of the interaction zone in laterally colliding plasmas has been investigated. As diagnostic tools, fast imaging and optical emission techniques were used to evaluate the characteristics of the seed plasma as well as the interaction zone created by different target materials (i.e., aluminum and silicon). The current findings show that the dynamical, spectral, and geometrical properties of the generated interaction zone are affected by the features of the ablated species and the geographical separation of the interacting plumes. The interaction of aluminum plume species results in a sharper, more intense, and more directed stagnation zone than that reported for silicon targets using a 450 nm filter. Furthermore, the investigation of the interaction area emission from both regions for aluminum (Al) and silicon (Si) plasma explains the variation in plasma properties in the stagnation zone. As a part of this work’s description, a comparative study of the dynamics and characteristics of the homogenous interaction region produced by colliding plasma plumes by laser ablation of flat Al and Si targets has been presented, which can provide deep insight into the characterization of colliding laser-produced plasma expansion and related physical and technical properties.

Numerical simulation of laser-produced plasma expansion on a droplet surface

In this study, a numerical model of the plasma expansion on a droplet surface based on the initial plasma method was proposed. The initial plasma was obtained through the pressure inlet boundary condition, and the effect of ambient pressure on the initial plasma and adiabatic expansion of the plasma on the droplet surface, including the effect on the velocity and temperature distribution, were investigated. The simulation results showed that the ambient pressure decreased, leading to an increase in the expansion rate and temperature, and therefore a larger plasma size was formed. Plasma expansion creates a backward driving force and eventually envelops the entire droplet, indicating a significant difference compared to planar targets.

Sub-Alfvenic Expansion of Spherical Laser-Produced Plasma: Flutes, Cavity Collapse and Field-Aligned Jets

Sub-Alfvenic Expansion of Spherical Laser-Produced Plasma: Flutes, Cavity Collapse and Field-Aligned Jets

Time evolution of copper-aluminum alloy laser-produced plasmas in vacuum

Spectral and transient image measurements of the spatiotemporal evolution of laser-produced plasma of copper-aluminum alloy in vacuum and corresponding radiation hydrodynamics simulations are reported. The visible spectrum and time resolved plasma plume images were obtained for time delays from 10-100 ns at different positions near the target surface using space and time-resolved spectroscopy and time-resolved transient imaging. Using a program developed for multi-element laser-produced plasma simulation based on the radiation hydrodynamics model combined with experimental spectrum, ion/electron densities and plasma temperature as well as their time evolutions were obtained. The temporal and spatial distribution characteristics for Cu and Al ions in the plasma are clarified. These results will be helpful for understanding the dynamics of the different ions during expansion of multi-element laser-produced plasma and its applications.

Water temperature as acoustic impedance control for efficient laser peening

Laser peening is a shock processing technology that shows great potential for enhancing the surface properties of metals. In the process of laser peening, a high-pressure shock wave can be obtained by covering the metal surface with a transparent overlay, which induces plasma confinement. The plasma confinement layer suppresses the expansion of laser-produced plasma to increase the shock wave pressure amplitude. The acoustic impedance of the plasma confinement layer is an influential factor for effective laser peening. In this study, to investigate the effect of controlling the acoustic impedance of water on laser peening, experiments were carried out by varying the water temperature. The results showed that in laser peening experiments, warm water with a temperature around 60 °C could significantly improve the mechanical performance of stainless steel, suggesting that a simple method has been developed for efficient laser peening.

Diagnosis of electron temperature and density in the early stage of laser-produced Si plasma expansion

We measured time-resolved spectra of laser-produced plasma of Si in a vacuum at the early phase evolution (30–100 ns) and found clear signs of spectral line broadening. Based on the measured line intensities of Si2+ and Si3+ ions, the Saha–Boltzmann method is used to diagnose the electron temperature. The Stark broadening of different high-charge ion lines is combined with a modified Griem semi-empirical formula to diagnose the electron density of Si plasma in the early evolutionary stage. The effects of self-absorption, natural broadening, and Doppler broadening on the spectral profiles were evaluated. We also conducted experiments to verify that current experimental conditions satisfied the local thermodynamic equilibrium conditions. Finally, time evolutions for the electron temperature and electron density in the early stage of plasma evolution were obtained.

Effect of expanding plasma on propagation of electromagnetic pulses by laser-plasma interaction

Experiments were performed using the Prague Asterix Laser System to study the effect of expanding plasma on electromagnetic pulse propagation (EMP) in the interaction chamber in an intensity regime of 1016 W cm−2. Similar to the interaction that occurs between radio waves and the ionosphere, the expansion of laser-produced plasma causes the vacuum chamber to be gradually filled with inhomogeneous plasma that interacts with the emitted EMP. Combining the space-time analysis of a plasma density inside the interaction chamber and the fast Fourier transform filtering of antenna signals, we have resolved the influence of the expanding plasma on space-time characteristics of EMP.

Ion and extreme ultraviolet emission features of CO2 laser produced Sn and SnO2 plasmas

The plasma plume expansion, ion debris and extreme ultraviolet (EUV) emission features of CO2 laser-produced Sn and SnO2 plasmas are investigated in this work. The expansion parameters of laser-produced plasma (LPP) are estimated using a fast-gated intensified charge-coupled device (ICCD) imaging system, while the ion debris is detected using a Faraday cup and the time-of-flight (TOF) method. Additionally, the EUV emissions from CO2 laser-produced Sn and SnO2 plasmas are measured using a grazing incidence flat-field spectrograph and EUV photodiodes. The ICCD images show that the SnO2 plasma plume has a broader edge when compared with that of the Sn plasma. Because of the differences between the thermodynamic parameters of the samples, the total ion number and the kinetic energy were both higher for the SnO2 plasma than for the Sn plasma. The maximum estimated conversion efficiencies (CEs) of the Sn and SnO2 plasmas were 1.1% and 0.9%, respectively; the difference is due to the lower Sn fraction in SnO2. The results of the angularly-resolved EUV emission measurements showed that the detected EUV energy decreases as the angle with respect to the laser axis increases.

Ion charge state and energy enhancement by axial magnetic field applied during laser produced plasma expansion

AbstractThe effects of axial magnetic field on the properties of the ions ejected from Nd:YAG laser (wavelength = 1064 nm, pulse duration = 6 ns) produced expanding Cu plasma were investigated. A plane Cu target, without and with 0.23 T axial magnetic field at its surface, was irradiated in the fluence range of 2–24 J/cm2. The ions emitted along the target surface normal were analyzed with the help of ion collector and time-of-flight electrostatic ion energy analyzer. The integrated ion yield, highest ion charge state, average ion energy, and energy of individual ion charge states were found to increase by application of the magnetic field. The initial parameters of the non-equilibrium plasma such as average ion charge, equivalent potential, electron temperature, electron density, Debye length, and transient electric field were estimated from the experimental results obtained without and with application of the magnetic field. The increase of ion yield and ion charge state by application of magnetic field are most probably due to the trapping of electrons in front of the target surface, which boosts up the electron impact ionization process. The ion energy increment due to the magnetic field is discussed in the frame work of electrostatic model for ion acceleration in laser plasma.

The influence of plasma shielding effect on laser-ablated copper samples: a focus on signal-to-background ratio and plasma expansion

AbstractThe influence of plasma shielding effect induced by ambient gas pressure and laser intensity on the laser-produced Cu plasma parameters, signal-to-background ratio (S/B) and expansion are experimentally and numerically investigated. A Q-switched Nd:YAG laser at 1064 nm at various intensities ranging from 2 to 7.1 GW/cm2 intensity (40–150 mJ) is used to produce Cu plasma in air, argon (Ar), helium (He), and neon (Ne) ambient gas at various pressures ranging from 5 to 1000 mbar. Laser-induced breakdown spectroscopy reveals that spectral radiation, S/B, electron temperature, number density, and front edge velocity of the plasma have an increasing trend up to a certain value of laser intensity and gas pressure. Afterwards, a saturation trend is achieved, which is attributed to the shielding and self-regulation effect. The numerical modeling of the laser-produced Cu plasma in the presence of air at atmospheric pressure is carried out using the MULTI radiation hydrodynamics code. We have shown that the feature of plasma shielding effect observed in the experiments can be reproduced using a continuum hydrodynamics model. Laser intensity at about 3.5 GW/cm2 is found to produce the highest S/B at 1000 mbar air. He, Ne, air, and Ar show the best S/B, respectively and the best S/B is found for air, Ar, He, and Ne at 10, 5, 10, and 20 mbar, respectively. The expansion of plasma plume is studied using a simple and effective technique based on probe laser absorption and scattering method. The plasma plume expansion through He, Ne, air, and Ar at 1000 mbar pressure has the highest velocity, respectively. The simulated results of strong shock wave model and Rankine–Hugoniot jump condition are fitted to the experimental data, which are then used to estimate the values of the ablation parameters.

Self-similar solution of laser-produced plasma expansion into vacuum with kappa-distributed electrons

Abstract The expansion of semi-infinite laser produced plasma into vacuum is analyzed with a hydrodynamic model for cold ions assuming electrons modeled by a kappa-type distribution. Self-similar analytic expressions for the potential, velocity, and density of the plasma have been derived. It is shown that nonthermal energetic electrons have the role of accelerating the self-similar expansion.

Magnetized relativistic electron–ion plasma expansion

The dynamics of relativistic laser-produced plasma expansion across a transverse magnetic field is investigated. Based on a one dimensional two-fluid model that includes pressure, enthalpy, and rest mass energy, the expansion is studied in the limit of λD (Debye length)≤RL (Larmor radius) for magnetized electrons and ions. Numerical investigation conducted for a quasi-neutral plasma showed that the σ parameter describing the initial plasma magnetization, and the plasma β parameter, which is the ratio of kinetic to magnetic pressure are the key parameters governing the expansion dynamics. For σ≪1, ion's front shows oscillations associated to the break-down of quasi-neutrality. This is due to the strong constraining effect and confinement of the magnetic field, which acts as a retarding medium slowing the plasma expansion.

Temporal evolutions of the plasma density and temperature of laser-produced plasma expansion in an external transverse magnetic field

The nanosecond laser produced plasma expansion in an external transverse magnetic field is explored by using optical imaging of plasma self-luminescence, optical spectrum and optical interferometry techniques. The plasma displays bifurcation and focusing phenomena in a transverse magnetic field, which is different from the scenarios without external magnetic field significantly. We set up a simplified magnetohydrodynamics model according to the feature of experimental parameters. The theoretical results of the temporal evolutions of the plasma density and the temperature are in good agreement with the experimental results, which confirms the important role of the magnetic diffusion in the plasma evolution.

Spectral and spatial structure of extreme ultraviolet radiation in laser plasma–wall interactions

Intense extreme ultraviolet (XUV) radiation was observed during the interaction of low-temperature laser plasmas and wall materials. Laser plasmas with electron temperature Te ∼ 40 eV were created on massive solid targets (CF2 and Al) by an excimer KrF laser (248 nm/0.5 J/13 ns/1 Hz). The wall was installed in the path of the laser-produced plasma expansion at distances between 0.5 and 3.5 mm. The spectral and spatial structure of XUV radiation (spectral range of λ ∼ 6–20 nm) was studied using a grazing incidence spectrometer with a back-illuminated CCD camera as a detector. XUV spectra of F and Al ions were analyzed. At large plasma–wall distances three-body recombination was identified as the dominant process responsible for ionic level population and radiation. The experiments demonstrate an effective way of creating low-temperature (Te ∼ 1–10 eV) plasmas interacting with solid surfaces (walls).

Effect of transverse magnetic field on laser produced plasma expansion into vacuum

A one-dimensional time-dependent magneto-hydrodynamic ideal model is used to investigate the dynamics of initially magnetized laser produced plasma expansion into vacuum, in the context of inertial fusion. The plasma is assumed to be fully ionized and in local thermodynamic equilibrium (LTE), allowing all charged particles to have the same temperatures. Self-similar solution shows that the density, velocity, and temperature increase with the strength of the magnetic field. The transverse magnetic field causes significant changes in the plasma expansion dynamics, including the plasma confinement. The plasma velocity increasing is also observed and the temperature is found to be larger compared to temperature in un-magnetized case.

On the use of shockwave models in laser produced plasma expansion

Interaction of medium to high peak power laser pulses with solid materials produces a plasma that expands supersonically. Expansions of such plasmas have been studied and several models have been proposed to describe it. This work presents a study of the expansion of laser produced plasmas in both vacuum and gas environment by using Langmuir probe and photography. It compares some of the most used models to identify that which better describes the expansion process. In vacuum, such process is properly described by the Anisimov model. However when expanding in a background gas it is found that the Sedov-Taylor model fits properly the position of generated shockwave but overestimates both kinetic energy and pressure of the expanding plasma. Such problem is solved by using a modification of the Freiwald-Axford model. Finally it is demonstrated that after the plasma stopping distance the plasma inters in a diffusive regime.

Multi-peak structure of the ion current in laser produced plasma

The experimental multi-peak structure of the transient ion current recorded by a charge-collector probe during the laser produced plasma expansion is reported for Sn and Li targets, and various focusing conditions and laser beam energies. Using a simple hydrodynamic model, the numerical simulations can reproduce well this type of behavior. Theoretically, a fractal hydrodynamic model is developed in a non-differentiable space-time. The solutions of Gaussian wave packet and ‘bouncing’ Gaussian wave packets types are found to explain the plasma expansion and to give a reasonable mathematical description of plasma splitting process.

Lateral confinement of laser ablation plasma in magnetic field

The expansion of copper laser-produced plasma along a magnetic field was investigated with the aim of confining the lateral expansion of the plasma. Time-resolved optical imaging, time- and space-resolved optical emission spectroscopy and time-of-flight Langmuir ion probe measurements were used to study the plasma dynamics. Thin films of copper were deposited without, and with, the magnetic field. It was observed that the magnetic field gives rise to substantial confinement of the plasma, leading to an increase by a factor of 6 in the ion yield and 2.6 in the deposition rate.

Interferometric investigations of influence of target irradiation on the parameters of laser-produced plasma jets

Our recent experimental results demonstrate that the formation of plasma jets is a fundamental process accompanying the laser produced plasma expansion, if a massive planar target with relatively high atomic number is irradiated by a defocused laser beam. In this paper some new results on the influence of target irradiation conditions on plasma jet parameters are presented. The experiment was carried out at the PALS iodine laser facility, with the third harmonic beam of the pulse duration of 250 ps (FWHM). The beam energies varied in the range of 13–160 J, the focal spot radii in the range of 35–600 µm. The planar massive targets used in the experiment were made of Cu, Ag and Ta. For measurements of the electron density evolution a three frame interferometric system was employed. The jets were observed in the whole range of the laser energy used. The initial velocities of the plasma jets produced in the reported experiment reached the value of up to 7·107 cm/s, the jets were up to 4 mm long including the jet pedestal and about 400 µm in diameter. Calculations of the efficiency of the plasma jet production show that it decreases with increasing the laser energy.