Laser-produced Aluminum Plasma Research Articles

Digital holographic measurement of electron temperature and density of laser-produced plasmas with an ultrashort laserpulse.

Holography, which can provide the information of phase as well as amplitude of a laser probe, could be a powerful method to diagnose the electron density and temperature of a plasma simultaneously. In this paper, digital holography with an ultrashort laser pulse is applied to diagnose laser-produced aluminum plasmas. Detailed analyses show that the reconstruction of the wave amplitude could be profoundly affected by the difference between the phase and group velocity of the ultrashort laser pulse in the plasma, which makes it a challenge to accurately reconstruct the amplitude in the case when ultrashort laser pulses are utilized for high-temporal resolution of holography.

Spatio-temporal dynamics of anisotropic emission from nano-second laser produced aluminium plasma

We report the polarization of spectral emission from aluminium plasma generated using a ns laser. The results show an interesting behaviour of polarization flips with the plasma plume propagation direction.

Anomalous time of flight behavior of fast ions in laser produced aluminum plasma

In this work, dynamics of multi-charged ions emitted from an aluminum plasma produced by Q switched Nd: Yag laser is studied using time of flight (TOF) measurements from Langmuir probe and spectroscopy under Ar ambient of 0.02 mbar. The temporal evolution of multi-charged ions, background neutrals, and ions is systematically studied for varying laser intensities. The temporal evolution shows all species have double-peak structure for all laser intensities considered in the study. The fast peak is sharp whereas the slow peak is broadly similar to that observed in previous studies. Moreover, higher charged ions have higher velocity, indicating acceleration from the transient electric field produced at the very initial temporal stages of expansion. Interestingly, the fast peak gets delayed, whereas the slow peak advances in time with increased laser intensity, which has not been reported in earlier studies. The observations point toward the possible role of ambipolar electric fields in the unexpected observed behavior of the TOF profiles.

Shock front interaction and dynamics of laterally colliding laser-produced plasmas

The effects of ambient gas pressure on the propagation dynamics of laterally colliding laser-produced aluminum plasma is investigated under various ambient conditions. In lower pressure range the interaction zone formed in between the seed plasmas exist for a short span of time. A strong stagnation region is observed at 10−2 mbar pressure in Ar ambient. Interaction zones are formed due to the shock waves generated at the seed plasmas at pressures above 0.1 mbar. A peculiar type of plume splitting is also observed at 0.15 mbar in air ambient at 150 ns. In Ar ambient, a channel like structure is observed in between the plasma plumes whose width increased with time. Shock interaction in air ambient is explained by regular reflection of shock waves where an illuminated interaction zone was formed where as in heavier Ar ambient, Mach reflection of shock waves occurs.

On the delayed emission from a laser-produced aluminum plasma under an argon environment

We report long time (250 μs) emission from Al I in laser produced plasma in argon ambient and its dependence on laser power density, background pressure and distance from the target surface. Role of argon metastables as energy reservoirs is discussed.

The role of nanoparticles concentration in the emission intensity enhancement of the laser-produced aluminum plasma

The nanoparticles-enhanced Laser-Induced Breakdown Spectroscopy (NELIBS) is an attractive technique to achieve the emission intensity enhancement of the LIBS spectrum. In this article, we present a study on the enhancement in the LIBS signals of seven different aluminum spectral lines using silver (Ag) nanoparticles on the surface of the Al target. The intensity enhancement factor of about 2–8 as compared with the conventional LIBS has been realized. The results showed an increase in the enhancement factor with the increasing concentration of the Ag nanoparticles. Plasma parameters, such as excitation temperature was estimated using the Boltzmann plot method whereas, the electron number density was estimated from the Stark broadened Al I lines. An increase in the excitation temperature and electron number density has been observed in NELIBS as compared with the conventional LIBS. Furthermore, the relative concentration of the neutral aluminum atoms estimated from the Boltzmann plot is found to be higher in NELIBS as compared with conventional LIBS. The presence of silver nanoparticles resulted in a better interaction of the laser beam with matter revealing enhanced emission intensity.

Temporal and Spectral Characterization of Electromagnetic Pulse Emitted From Nanosecond Pulsed Laser Produced Aluminum Plasma

The electromagnetic pulse (EMP) emitted from the plasma produced by interaction of 5-ns pulsed Nd:YAG ( $\lambda =532$ nm) laser with the aluminum target was measured. The laser irradiance at the target was varied in the range of $3.12\times 10^{9} - 4.56\times 10^{10}$ W/cm2 and its influence on the temporal and spectral parameters of the EMP was investigated. The EMP starts well after the termination of laser pulse and the duration of EMP is up to several hundred nanoseconds. The EMP start time was found to decrease from approximately 150 to 60 ns with the rise of laser irradiance. The rise time of EMP (~50 ns) does not seem to vary with the laser irradiance. The signal consists of several resonance peaks in the frequency bin of 20–200 MHz, whose intensity also depends on the laser irradiance. The observed dependence of EMP intensity on the laser irradiance and frequency of fundamental-mode emission is compared with the theoretical predictions. The considerable delayed emission of EMP indicates that its origin can be related to the macroscopic charge separation phenomena during the plasma expansion.

Effects of continuous phase plate on plasma corona homogeneity and laser-plasma instabilities in experiments with three target materials

Corona homogeneity and spectra of scattered light and hot electrons produced by laser-plasma instabilities inside laser-produced plastic, aluminum, and gold plasmas were investigated with and without the use of continuous phase plate (CPP) to the laser beam. Improvement of the corona homogeneity was observed for all three materials after applying CPP, while the inhibition of the intensity of backward-scattered light and the amount of emitted hot electrons was not always synchronous for different materials, which is interpreted as a result of the changes in thresholds of the stimulated Raman scattering (SRS) and the two-plasmon decay (TPD) instability before and after the application of CPP. By comparing the changes of SRS scattered light intensity with the amount of hot electrons in different kinetic energy ranges for all three target materials in our experiments, we conclude that SRS is more responsible for the diagnosed hot electrons between 50–150 keV, and those above 150 keV should be generated by TPD, which could be explained by the difference in phase velocity of electron plasma waves between SRS and TPD calculated from measured and simulated parameters of corona and laser-plasma instabilities.

Effect of laser beam size on the dynamics of ultrashort laser-produced aluminum plasma in vacuum

In laser-produced plasma experiments, the diameter of the irradiating laser beam on the target surface is a major parameter that influences the ablation mechanisms, plasma emission intensity, charged particle ejection, and plume morphology. In this work, the expansion dynamics of an ultrashort laser-produced aluminum plasma is investigated as a function of the laser beam size on the target, using a combination of diagnostic tools, viz., optical emission spectroscopy, fast gated time-resolved imaging, and ion current measurements. A Ti:sapphire laser delivering 100 fs, 6 mJ pulses at 800 nm is used for producing plasma from a pure Al target placed in vacuum (10−5 Torr) at different positions with respect to the geometrical focus of the beam. Optical emission spectroscopic analysis of the plasma shows that higher emission intensities and ion populations are obtained for smaller beam sizes. Time-resolved Intensified Charge Coupled Device (ICCD) imaging of the expanding plasma shows a spherical morphology for plumes produced by smaller beam sizes and a cylindrical morphology for those produced by larger beam sizes. Temporal profiles of ion emission measured using a Faraday cup are in agreement with ICCD data, featuring a dual peak structure for larger beam sizes indicating distinct slow and fast ionic species, arising from changes in the ablation mechanism for varying laser fluences. Plume expansion is modelled by free expansion for the fast species and by shock wave propagation for the slow species. Ion flux and velocities are relatively high for smaller beam sizes. These studies can be of potential importance for laser processing applications, including laser welding, drilling, and micromachining.

Ion dynamics of a laser produced aluminium plasma at different ambient pressures

Plasma is generated by pulsed laser ablation of an Aluminium target using 1064 nm, 7 ns Nd:YAG laser pulses. The spatial and temporal evolution of the whole plasma plume, as well as that of the ionic (Al2+) component present in the plume, are investigated using spectrally resolved time-gated imaging. The influence of ambient gas pressure on the expansion dynamics of Al2+ is studied in particular. In vacuum (10−5 Torr, 10−2 Torr) the whole plume expands adiabatically and diffuses into the ambient. For higher pressures in the range of 1–10 Torr plume expansion is in accordance with the shock wave model, while at 760 Torr the expansion follows the drag model. On the other hand, the expansion dynamics of the Al2+ component, measured by introducing a band pass optical filter in the detection system, fits to the shock wave model for the entire pressure range of 10−2 Torr to 760 Torr. The expansion velocities of the whole plume and the Al2+ component have been measured in vacuum. These dynamics studies are of potential importance for applications such as laser-driven plasma accelerators, ion acceleration, pulsed laser deposition, micromachining, laser-assisted mass spectrometry, ion implantation, and light source generation.

Comparison of the polarisation of line and continuum emission in a laser produced plasma

Anisotropic emission from a laser-produced aluminium plasma emission has been studied using time and polarisation resolved spectroscopy. The time-resolved degree of polarisation of emission from a bound – bound transition in Al+ (466.3 nm) was compared to the time-resolved degree of polarisation from nearby continuum emission. The results are interpreted in the framework of radiative recombination and statistical imbalances in the populations of magnetic sub-states. It is found that the continuum emission is more strongly polarised than the line emission. Thus, this technique is a valid alternative to gated LIBS.

Time resolved anisotropic emission from an aluminium laser produced plasma

The polarisation anisotropy of the emission from a laser produced aluminium plasma has been studied using time and polarisation resolved spectroscopy at various background pressures of air. A Wollaston prism was used to resolve the emission from the plasma into polarisation components that are parallel and orthogonal to the plasma expansion axis. Spectroscopy reveals that as the background pressure is increased, strongly polarised continuum emission dominates at early stages of the plasma formation. The results are compared and contrasted to similar experiments and discussed in the framework of a recombining plasma.

Time evolution analysis of dynamics processes in laser-produced Al plasmas based on a collisional radiative model

The temporal evolution of extreme ultraviolet emission from a laser-produced aluminum plasma has been experimentally and theoretically investigated. Spectra of highly charged Al ions have been measured by using the temporal-spatially resolved laser-produced plasma emission technique. In order to deeply understand the evolution of plasmas and achieve the purpose of rapid diagnosis, a collisional-radiative model has been resolved in the steady-state and time-dependent cases, respectively. The evolution of rate coefficients as a function of the electron temperature, electron density, and time delay has been discussed, respectively. In addition, the influence of the photo-ionization process has also been evaluated for the ionization balance. The results indicate that the time evolution analysis of spectra is useful for the accurate understanding of the evolution behavior of highly charged ions in laser-produced plasmas.

K-shell X-ray spectroscopy of laser produced aluminum plasma

Optimization of a laser produced plasma (LPP) X-ray source has been performed by analyzing K-shell emission spectra of Al plasma at a laser intensity of 1013–1014W/cm2. The effect of varying the laser intensity on the emissivity of the K-shell resonance lines is studied and found to follow a power law, Ix=(IL)α with α=2.2, 2.3, 2.4 for Heβ, Heγ, Heδ respectively. The emission of these resonance lines has been found to be heavily anisotropic. A Python language based code has been developed to generate an intensity profile of K-shell spectral lines from the raw data. In theoretical calculations, the temperature is estimated by taking the ratio of the Li-like satellite (1s22p–1s2p3p) and the Heβ (1s2–1s3p) resonance line and the ratio of the He-like satellite (1s2p–2p2) and the Lyα (1s–2p) resonance line. To determine the plasma density, stark broadening of the Lyβ spectral line is used. Simulation was carried out using the FLYCHK code to generate a synthetic emission spectrum. The results obtained by FLYCHK are Te=160eV, Th=1keV, f=0.008, ne=5×1020cm-3 and the analytical model resulted Te=260–419eV and ne=3x1020cm-3.

Investigation of temporal-resolved emission spectra of highly charged Al ions from laser-produced plasmas

Temporal evolution of extreme ultraviolet emission from laser-produced aluminum (Al) plasma has been experimentally and theoretically investigated. Al plasmas have been measured by using the temporal-spatially resolved laser-produced plasma technique. The emission lines can be identified from 2p-3s, 3d, 4s, 4d, 5d transition lines from Al3+ to Al6+ ions. In order to quickly diagnose the plasma, the assumptions of a normalized Boltzmann distribution among the excited states and a steady-state collisional-radiative model are used to estimate the values of electron temperature and electron density in plasma. We succeeded in reproducing the simulated spectra related to the different time delays, which are in good agreement with experiments. Temporal evolution behavior of highly charged Al ions in plasma has been analyzed, and the exponential decay about electron temperature and electron density has been obtained. The results indicate that the temporal-spatially resolved measurement is essential for accurate understanding of evolution behavior of highly charged ions in laser-produced plasmas.

A quantitative study of the forbidden and intercombination transitions arising from the Li-like Al autoionizing levels

This work presents results from detailed quantitative description of the level population kinetics responsible for the relatively high line-intensity of the forbidden and intercombination transitions arising from autoionization states. The goal is to investigate the influence of different atomic processes on the emission spectrum of the laser-produced aluminum plasma obtained at the nhelix-laser test bed facility at GSI (PRA 63, 032716). In the experiment a Nd-glass YAG laser beam having 50 J pulse energy, 15 ns full width half maximum duration and 1.064 μm wavelength is focused on a massive Al target. To simulate the experimental reported spectrum, the population kinetics is investigated based on a collisional radiative model. The theoretical spectroscopic investigation reported here indicates the existence of anomalous high intensity X-ray intercombination and two-electron transitions arising from autoionizing states in Li-like Al ion. Detailed atomic structure calculation and kinetics modeling is performed to find out the individual states involved, and the population density distribution over them. Presented results are useful for femtosecond-laser produced plasma experiments and diagnostics.

Ion flux enhancements and oscillations in spatially confined laser produced aluminum plasmas

Ion signals from laser produced plasmas (LPPs) generated inside aluminum rectangular cavities at a fixed depth d = 2 mm and varying width, x = 1.0, 1.6, and 2.75 mm were obtained by spatially varying the position of a negatively biased Langmuir probe. Damped oscillatory features superimposed on Maxwellian distributed ion signals were observed. Depending on the distance of the probe from the target surface, three to twelve fold enhancements in peak ion density were observed via confinement of the LPP, generated within rectangular cavities of varying width which constrained the plasma plume to near one dimensional expansion in the vertical plane. The effects of lateral spatial confinement on the expansion velocity of the LPP plume front, the temperature, density and expansion velocity of ions, enhancement of ion flux, and ion energy distribution were recorded. The periodic behavior of ion signals was analyzed and found to be related to the electron plasma frequency and electron-ion collision frequency. The effects of confinement and enhancement of various ion parameters and expansion velocities of the LPP ion plume are explained on the basis of shock wave theory.

Investigation of dominant states for dielectronic recombination in short-pulse laser-produced aluminum plasma

AbstractThis paper presents the results of relativistic calculation intended specifically to investigate the dominant states for dielectronic recombination of Li-like into Be-like Al ions in short-pulse laser produced plasmas. The relativistic Dirac R-matrix calculation is performed to output resonance energy levels and rates. The target energies and orbitals are calculated with the extended average level multi-configurational Dirac-Fock method in the general-purpose relativistic atomic structure package. This type of calculation gives a set of 13 bound orbitals that is optimized over all the levels included. The resulting 13 relativistic orbitals produced 74 Jπ levels, all of which are to be used in the close-coupling expansion. To the best of our knowledge, the work reported herein describes for the first time such detailed calculation for this atomic system and the results are relevant to the short-pulse laser produced plasma modeling.

Measurements of Plasma Electron Temperature Utilizing Magnesium Lines Appeared in Laser Produced Aluminum Plasma in Air

We have utilized the relative intensity of magnesium lines originated from the Mg I at 285.2 nm and Mg II at 280.27, 279.55 nm to measure the plasma electron temperature. The plasma was produced via interaction of Nd:YAG laser with solid aluminum target contains traces of magnesium. The magnesium lines were found to suffer from optical thickness which manifests itself on the form of scattered points around the Saha-Boltzmann line. We have utilized a simple method used for rapid calculation to the amount of absorption to these lines via comparison of the electron densities as deduced from magnesium lines to that evaluated from the optically thin hydrogen Hα line at 656.27 nm appeared in the same spectra under the same condition. A correction to the magnesium spectral lines intensities was carried out; hence the corrected temperatures were re-evaluated. The measurements were repeated at different delay times ranging from 1 to 5 μsec. This work emphasizes on the importance of correcting the emitted spectral line intensity against the effect of self absorption before using them in the calculation of plasma electron temperature in laser induced breakdown spectroscopy (LIBS) experiments.

Space-Resolved Diagnosis for Electron Temperature of Laser-Produced Aluminum Plasma

The K-shell emission spectra of laser-produced aluminum plasma are measured by a space-resolved spectrometer consisting of a flat crystal spectrometer with a 20 μm wide space-resolved slit. By using the approximation of the steady collisional-radiative equilibrium model, the interstage line intensity ratios of Ly-α resonance line to He-α resonance line are given as a function of electron temperature. The spectra profiles are decomposed to resonance line and the overlapped high-order satellites manifold. Thus reliable electron temperature is deduced from the interstage line intensity ratios of the decomposed resonance lines. The results of spaced-resolved temperature are compared with the hydrodynamic simulations. The diagnostics of electron temperature for laser-produced plasma is developed.