Laser-produced Al Plasma Research Articles

Material-specific high-order harmonic generation in laser-produced plasmas for varying plasma dynamics

We present a new experimental setup for high-order harmonic generation in laser-produced plasmas, allowing the generation of coherent VUV and EUV light, as well as characterisation of the laser-produced plasmas by studying the emitted harmonics. We have successfully generated high-order harmonics in laser-produced Al, Ni, Ag, In, and Sn plasmas. Large differences in harmonic spectra and signal yields have been observed for these different targets. Harmonics up to order 25, corresponding to a wavelength of 62.4 nm and photon energy of 19.9 eV, have been measured with tin plasmas. Scanning laser parameters and delay between pump and fundamental laser pulses allows us to optimise the harmonic yield and observe the temporal dynamics of the laser-produced tin plasma.

Real optical imaging simulation of laser-produced aluminum plasmas.

We developed a post-processing optical imaging model based on two-dimensional axisymmetric radiation hydrodynamics. Simulation and program benchmarks were performed using laser-produced Al plasma optical images obtained via transient imaging. The emission profiles of a laser-produced Al plasma plume in air at atmospheric pressure were reproduced, and the influence of plasma state parameters on radiation characteristics were clarified. In this model, the radiation transport equation is solved on the real optical path, which is mainly used to study the radiation of luminescent particles during plasma expansion. The model outputs consist of the electron temperature, particle density, charge distribution, absorption coefficient, and corresponding spatio-temporal evolution of the optical radiation profile. The model helps with understanding element detection and quantitative analysis of laser-induced breakdown spectroscopy.

Experimental setup for interaction between highly charged ions and laser-produced plasma near Bohr velocity energy region

Ion energy loss in the interaction between highly charged ions and dense plasma near Bohr velocity energy region is one of the important physical problems in the field of high-energy density physics driven by intense heavy ion beams. Based on the 320 kV experimental platform at the Institute of Modern Physics, Chinese Academy of Sciences, a new experimental setup was built for the research of interaction between ions and laser-produced plasma near the Bohr velocity, where the ion energy loss and charge state distribution can be experimentally investigated. In this paper we introduce the new setup in detail, including the generation and controlling of pulsed ion beam ( ≥ 200 ns); the preparation of high-density laser plasma target (10<sup>17</sup>—10<sup>21</sup> cm<sup>–3</sup>); the diagnostics of plasma and the developed high energy resolution ion measurement system (< 1%). In the experiment, the charge distribution of Xe<sup>15+</sup> ions with 4 MeV penetrating through the laser-produced Al plasma target is measured. The charge-state analysis device observes different results without and with the plasma, in which the outgoing Xe ion charge-state changes correspondingly from the 15+ to 10+, thus the electron capture process is believed to be dominant. In addition, the proton energy loss is also measured by using the magnetic spectrometer, showing that the experimental energy loss is about 2.0 keV, 30% higher than those theoretical predictions , which can be attributed to the fact that in the near Bohr velocity energy regime, the first-order Born approximation condition is not valid, thus the Bethe model and SSM model are inapplicable to the experimental results. In future, a systematic study will be performed based on our ions-plasma ineteraction setup, and the energy loss and charge state data will be introduced.

X-ray spectroscopy of laser produced Al plasma near the target surface in a laser ion source

The spatially resolved x-ray spectrum of a laser produced Al plasma near the target surface has been obtained in the energy range of 1.5–2.2 keV using a compact flat crystal spectrometer. The widely used temperature and density diagnostics, the line ratios of Lyα/Heβ and IC/Heα, were measured and compared with the calculation results of a steady-state collisional-radiative model so that the temperature and density profiles with a spatial resolution of 55 µm were obtained within 200 µm from the target plane. The plasma parameters derived from the spatially integrated spectrum were used to calculate the ionization state distribution near the target surface with the steady-state model, and the result was compared with the ion charge state distribution measured with an Electrostatic Ion Analyzer (EIA) at a distance of 4.2 m from the target surface. The validity of the steady-state model and the difference between the calculated ion charge state distribution and that measured with the EIA are discussed.

Investigation on the charge-state distribution diagnosis oflaser-produced Al plasmas

Laser-produced plasmas (LPP) have been known to possess great application potential under extreme ultraviolet (EUV) lithography, soft X-ray micrography, and heavy ion accelerator, highly charged ion optical frequency standards, pulsed laser deposition, astrophysics and nuclear fusion. The applications in these fields require a clearer understanding of the evolutionary behavior of the LPP. However, LPP is neither homogeneous nor static during their expanding and cooling process, which involves complex physical processes. For a deep understanding of the LPP, many diagnostic methods and techniques have been developed, such as spectroscopy, fast imaging, time-of-flight (TOF), laser interferometry and Thomson scattering. Among these methods, spectroscopy has been the most widely used diagnostic method, which can be used to obtain relatively more state information. However, the diagnosis results of charge-state distribution obtained by spatio-temporally resolved spectroscopy are local and transient, and cannot therefore obtain the overall distribution. In order to have a more comprehensive understanding of charge-state distribution and its evolutionary behavior of the LPP, other diagnostic methods are needed. The TOF method is used for the measurement of highly charged ions of the LPP, which can be used to obtain the overall charge-state distribution information. Therefore, in this work, spectrometry and TOF method were used for the diagnosis of charge-state distribution of the LPP in a vacuum. The EUV emission spectra of laser-produced Al plasmas were measured by using spatio-temporally resolved laser-produced plasmas spectroscopy technique. The charge-state distributions with different delay times at the distance of 2.0 mm from target surface were diagnosed by spectral simulation and their evolution behavior were also analyzed. The TOF spectra of laser-produced Al plasmas were measured by the TOF method, and the overall charge-state distribution of ions in laser-produced Al plasmas was obtained. The results revealed that spectroscopy can diagnose the local and transient charge-state distribution of ions in the laser-produced plasmas, and the TOF method can be used to diagnose its overall distribution, and the two diagnostic methods therefore complement each other. This work aims to clarify the complementarity of the two methods, and to provide a method support for the comprehensive and accurate understanding of the charge-state distribution and evolution evolutionary behavior during the expansion process of the LPP, and also provides a reference for further optimization and modification of the radiation hydrodynamics model of the LPP.

Effects of laser wavelength on aluminum plasma in transverse magnetic fields

The influence of the laser wavelength on nanosecond laser-produced Al plasma in a transverse magnetic field is studied and presented. A Q-switch Nd:YAG pulsed laser (FWHM: 6 ns) is used to ablate an aluminum sample at 50 mJ at the fundamental, second, and fourth harmonics of 1064 nm, 532 nm, and 266 nm, respectively. A permanent magnetic trap is used with a nearly uniform magnetic field of 0.8 T to confine plasma expansion, reduce both fast and slow components of plasma velocity, and increase signal intensity. Fast photography is performed using an Intensified Charged Coupled Device camera to study the plume hydrodynamics as it evolves through the induced magnetic field. Optical Emission Spectroscopy is used to determine the effect of the laser wavelength on key ionic and neutral emission lines, as well as to study the enhancement and reduction of certain emission lines in the presence of a magnetic field. Fast photography results confirm that the laser wavelength has a significant effect on plume hydrodynamics, especially as it evolves through the magnetic field. The magnetic field confines both fast and slow components of the plasma as early as ∼45 ns after laser impact for all laser wavelengths used, as well as reducing the velocity of the plasma by about 5×. It is shown that the 266 nm laser wavelength under the magnetic field enhanced both ionic and neutral lines by up to 11×, while 532 nm laser plasma only showed enhancements in ionic lines with reduction in neutral. A laser wavelength of 1064 nm showed a slight enhancement of ionic lines with a significant reduction in neutral lines under the same conditions.

Energy Spectrum and Charge Composition of Ions of Laser-Produced Gd and Al Plasmas

The energy spectrum and the distribution of the total charge over the ion energy are studied for plasma produced by partially coherent radiation of the neodymium glass laser with a power density of ~1013 W/cm2 in the focusing spot incident on continuous gadolinium (Gd) and aluminum(Al) plates. The spectra of plasma ions for gadolinium and aluminumtargets are presented at laser radiation energies of 2, 7, 20 J and 1 J, respectively. For the gadolinium target, an increase in the peak amplitudes in ion spectra with increasing influencing radiation energy and manifestations of higher-energy ions are observed. The difference in the ion emission for gadolinium and aluminum targets is also recorded at close radiation energies of 2 and 1 J, respectively.

Spatio-temporally resolved spectral measurements of laser-produced plasma and semiautomated spectral measurement-control and analysis software

A spatio-temporally resolved spectral measurement system of highly charged ions from laser-produced plasmas is presented. Corresponding semiautomated computer software for measurement control and spectral analysis has been written to achieve the best synchronicity possible among the instruments. This avoids the tedious comparative processes between experimental and theoretical results. To demonstrate the capabilities of this system, a series of spatio-temporally resolved experiments of laser-produced Al plasmas have been performed and applied to benchmark the software. The system is a useful tool for studying the spectral structures of highly charged ions and for evaluating the spatio-temporal evolution of laser-produced plasmas.

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.

Spatial-Resolved Measurement and Analysis of Extreme-Ultraviolet Emission Spectra from Laser-Produced Al Plasmas**Supported by the National Natural Science Foundation of China under Grant Nos 11064012, 11364037 and 11564037, the Basic Scientific Foundation of Higher Learning of Gansu Province, and the Natural Science Foundation of Gansu Province under Grant Nos 1308RJZA166 and 1104WCGA186.

Extreme ultraviolet emission from laser-produced Al plasma is experimentally and theoretically investigated. Spatial-evolution emission spectra are measured by using the spatio-temporally resolved laser produced plasma technique. Based on the assumptions of a normalized Boltzmann distribution among the excited states and a steady-state collisional-radiative model, we succeed in reproducing the spectra at different detection positions, which are in good agreement with experiments. The decay curves about the electron temperature and electron density, as well as the fractions of individual Al ions and average ionization stage with increasing the detection distance are obtained by comparison with the experimental measurements. These parameters are critical points for deeply understanding the expanding and cooling of laser produced plasmas in vacuum.

A K-shell model for laser-produced Al plasma

The spectra from laser-produced plasma have been simulated by the newly developed model. The simulation agrees well with the experimental results, which can prove that the K-shell model is suitable for the application of the spectrum from laser-produced plasma. Also, the jkl satellite lines were found important for predicting the spectra.

Fast ion generation in the cathode plasma jet of a multipicosecond laser-triggered vacuum discharge

Ion generation in the cathode plasma jet of a moderate-current (approximately 2.3 kA), low-energy (< or = 20 J) vacuum spark discharge triggered by approximately 27 ps, 10 mJ laser pulses is studied using time of flight technique. Fastest ion velocity and velocity corresponding to the peak of the time of flight signals for Al cathode were measured to be approximately 5.25x10(8) cm/s (energy of approximately 143 keV/u) and approximately 8.1x10(7) cm/s (energy of approximately 3.4 keV/u), respectively. Corresponding velocities in the case of ions generated from laser-produced Al plasma (energy of approximately 550 mJ, intensity of approximately 10(14) W/cm(2)) were found to be much smaller, viz., approximately 1.05x10(8) cm/s (energy of approximately 5.75 keV/u) and approximately 2.63x10(7) cm/s (energy of approximately 0.36 keV/u), respectively. Study shows efficient acceleration of ions in a current-carrying cathode plasma jet of a small-energy multipicosecond laser-triggered spark discharge as compared with that in a high-energy multipicosecond laser-produced plasma plume.

Kilovolt radiation from a laser-produced Al plasma

We have characterized kilo-electron-volt (keV) emission from Al plasmas for various laser illuminations at the OMEGA laser with the goal of optimizing the ability to backlight low-atomic-number materials such as beryllium for fusion ignition studies. The plasma is diagnosed by spectral-measurement comparisons to detailed theoretical atomic physics models. It is found that a significant fraction of the radiation is due to the x-ray continuum, that the electron temperature Te depends weakly on laser energy and power, and that the conversion efficiency to Lyman α (Lα, the N=2→1 transition in H-like Al) at 1.73 keV is reduced as laser energy is increased. As the number of beams is increased, the extra laser energy goes into a larger, higher-density plasma in which He-like and H-like ions are more effectively ionized.

Measurement of the degree of polarization of the spectra from laser produced recombining Al plasmas.

Using a polarization-resolved UV-visible spectrometer, the degree of polarization of the spectra from laser produced Al plasmas was measured. The polarization resolution was achieved by using either a dichroic polarizer or a calcite crystal. The degree of polarization of Al III 4s(2)S(1/2)-4p(2)P(o)(3/2) transition at 569.66 nm was measured at different positions from a target surface. The degree of polarization was observed to be 2.1+/-0.13% at a distance of 220 microm from the target and decreased as the distance from the target increased, vanishing at a distance of about 1.3 mm from the target. To avoid the possible error due to the shot-to-shot variation of the line intensity, a calcite crystal was used to simultaneously observe the two polarization components, obtaining a similar result. The electron temperature of about 3 eV and the density of 2 x 10(17) cm(-3) measured spectroscopically indicates that the plasma was in the recombining phase. This is a report on the observation of the polarization of a transition in a laser-produced recombining Al plasma.

Measurement of the degree of polarization of the spectra from laser-produced Al plasma

Using a polarization-resolved UV–visible spectrometer, the degree of polarization of the spectra from laser-produced Al plasma was measured. To generate the Al plasma, Q-switched Nd/glass laser was used. The pulse duration of the laser is 3 ns and the energy per pulse is 6 mJ. The degree of polarization of Al III 4s 2 S 1/2 –4p 2 P 3/2 0 transition was measured at different positions from a target surface using a space and polarization-resolved spectrometer. To resolve the different polarization components of the emission line, a dichroic polarizer was used in front of the entrance slit of the spectrometer. The degree of polarization was observed to be 2.1±0.13% 220 μm from target surface and decreased as the distance from the target increased, vanishing about 1.3 mm from the target surface. To avoid the possible error due to the shot-to-shot variation of the line intensity, a calcite crystal was used to simultaneously observe the two polarization components. Both measurements yielded the same result. The plasma parameters, such as the electron temperature and density, were estimated by spectroscopic methods. The measured electron temperature was about 3 eV and the density was 2×10 17 cm −3 near the target surface and decreased to 4×10 16 cm −3 1.3 mm away from the target surface.

Detailed-term-accounting-approximation simulation of x-ray transmission through laser-produced Al plasmas

An extensive configuration interaction (CI) scheme and the R-matrix method are combined to calculate the x-ray transmission spectrum for high-power laser-produced Al plasmas in local thermodynamic equilibrium by using the detailed-term-accounting (DTA) approximation. All atomic parameters such as state levels and photoabsorption cross sections for different ionization stages are obtained by using the CI and R-matrix method. Special attention is given to the effects of autoionizing resonance broadening on the transmission. A large difference exists between the convergence of the results with and without taking account of autoionizing resonance broadening when the autoionization resonance broadening is the major broadening mechanism. This shows that autoionizing resonance widths of the K-shell excited states have large effects and should be considered to interpret the spectral-resolved transmission.

Investigations of ion emission from picosecond laser-produced Al plasma

The results of a detailed study of the ion emission from Al target irradiated with a high-intensity (up to 5 · 1016 W/cm2)1−ps Nd: glass laser pulse are presented. The ion emission measurements were based on the time-of-flight method. An electrostatic ion energy analyzer and ion collectors were employed. The maximum ion energy of about 132 keV and fully striped Al ions were registered. The ion current density of 3 mA/cm2 was measured at the distance of 1 m in the direction of the target normal. Both the measured ion charge distribution and the angular distribution of ion emission are discussed. The dependencies of the parameters of ions emitted from the plasma on the laser-pulse energy as well as on the location of the focus of the laser beam with respect to the target surface were also established.

Investigation of a laser driven vacuum diode X-ray source of photon energy ∼5 keV

An investigation of a monochromatic point X-ray source of photon energy ∼5 keV was carried out. The source was set up using a laser produced Al plasma as a cathode and a point-tip Ti anode. Optimum parameters of the diode were determined from experimental measurements of X-ray intensity dependence on laser pulse energy, applied accelerating voltage, and distance between target (cathode) and anode, using Nd:glass laser pulses (FWHM 30 ns) of 2 mJ to 4 J energy. Electron temperature characterization of the target plasma was also performed from the XUV emission spectrum (5–80 Å). Parameters of X radiation in Ti K-shells are (1) spectral brightness of ∼1020 photons/cm2-sec-sr-keV, (2) spatial size ∼300 microns, and (3) X-ray pulse duration less than 20 ns.

Effect of ionization and recombination coefficients on the charge-state distribution of ions in laser-produced aluminum plasmas

Various formulations for the ionization and recombination coefficients reported and used in the literature have been compared for laser-produced Al plasmas. Taking into account these formulations, the charge-state distribution of the plasma ions existing in various ionization states through their fractional densities and average charge state has been studied. The local thermodynamic, corona, and collisional-radiative equilibria are considered for the ionization model. Numerical results for Al plasmas with electron temperatures of 0.1{endash}1.0 keV and electron densities of 10{sup 20}{endash}10{sup 22}cm{sup {minus}3} are presented and discussed. It is observed that the several formulations for the ionization and recombination coefficients predict variously their rates. The consideration of these formulations in an ionization model is noted to significantly modify the charge-state distribution of the ions. It is further noted that the corona equilibrium model can be safely applied to laser plasmas with electron densities less than or equal to 10{sup 22}cm{sup {minus}3} for estimating the abundance of high-charge ions relevant to x-ray line radiation studies. {copyright} {ital 1997} {ital The American Physical Society}

Thermoluminescent dosimetry of x-ray radiation emitted from a laser-produced plasma

Thermoluminescent dosemeters of LiF:Mg,Ti (TLD 100), LiF:Mg,Cu,P (GR 200A) and (TLD 200) were used as detectors for absolute brightness measurements of x-ray emission from a laser-produced plasma. The influence of very short (nanosecond) exposure of the dosemeters by x-ray radiation from a keV spectral range is discussed. Thermoluminescent glow curves of (TLD 200) irradiated by x-ray radiation from radionuclide standards and laser-produced Al or Cu plasmas are analysed applying deconvolution based on general TL kinetics. The dependence of the ratios of areas of low-temperature single glow peaks on x-ray photon energy from 1 to 55 keV is shown.