Ions In Laser-produced Plasmas Research Articles

Radiation properties and hydrodynamics evolution of highly charged ions in laser-produced silicon plasma

SynopsisWe present a simplified radiation hydrodynamic model based on the fluid dynamic equations and the radiative transfer equation, which can be used to investigate the radiation properties and dynamics evolution of highly-charged ions in a laser-produced plasma in vacuum.

4d excitation spectra of highly charged Pr ions in laser-produced plasmas

Spectra of laser-produced praseodymium (Pr) plasmas have been acquired for the 7.5–14.5 nm wavelength range using spatio-temporally resolved emission spectroscopy. The characteristic features of experimental spectra are dominated by an intense narrow band and a broad quasi-continuous band. These derive from 4d-4f transitions of Pr3+ up to Pr7+ ions, according to Hartree-Fock calculations that evaluated configuration interaction effects. Plasma parameters have been estimated by comparing experimental and simulated spectra, based on the assumption of a normalized Boltzmann distribution among excited states and a steady-state collisional-radiative model. The results provide further understanding of radiation properties of highly charged ions of middle- and high-Z elements.

Opacity effects on soft X-ray spectra from highly charged lanthanide ions in laser-produced plasmas

We have observed soft X-ray spectra from highly charged ions of seven different lanthanide elements with atomic numbers ranging from 60 to 70 in laser-produced plasmas (LPPs) using CO2 and Nd:YAG laser systems, the wavelengths of which are 10.6μm and 1.064μm, respectively. The spectral feature drastically changes between the two types of LPPs due primarily to the difference in opacity. Narrowband quasicontinuum features arising from n=4–4 transitions, the centre wavelength of which systematically moves to shorter wavelength as the atomic number (Z) increases, are observed in the CO2 LPPs, accompanied by sharp peaks coinciding with the strongest resonance lines of Pd-like ions for lower Z elements. In contrast, the quasicontinuum bands are broader and smoother in the Nd:YAG LPPs, appearing with bands of n=4–5 transitions on the shorter wavelength side. The results are also discussed based on comparisons with atomic structure calculations for ions with outermost 4d and 4f subshells.

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.

Radiation properties and hydrodynamics evolution of highly charged ions in laser-produced silicon plasma.

We present a simplified radiation hydrodynamic model based on the fluid dynamic equations and the radiative transfer equation, which can be used to investigate the radiation properties and dynamics evolution of highly charged ions in a laser-produced plasma in vacuum. The outputs of the model consist of the evolution of the electron temperature, atom, and ion density, and the temporal and spatial evolution of various transient particles in plasma, as well as the simulated spectrum related to certain experimental conditions in a specified spectral window. In order to test the model and provide valuable experimental feedback, a series of EUV emission spectra of silicon plasmas have been measured using the spatio-temporally resolved laser produced plasma technique. The temporal and spatial evolution of the plasma is reliably reconstructed by using this model.

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.

Irradiation Effects of 40 – 250 keV Fe ions on Structural and Optical Properties of CR-39 Polymer

A passive Q-switched Nd:YAG pulsed laser was used to irradiate 99.99% pure Fe target in vacuum ∼10-3 Torr. The CR-39 specimens were exposed to laser produced plasma ions (40-250 keV) emitted along the normal to the Fe target surface. The flux of Fe ions was varied by varying the number of laser shots in the range 500-1500 with an increment of 250. A comparison of structural and optical properties of CR-39 polymer before and after ion implantation was made. The increase in ion flux leads to the transformation of polymer into rather more disordered amorphous state leading to the broadening of XRD peaks. The crystallite size decreases (3.547 to 1.618nm) and Urbach energy increases (0.232 to 0.291eV) exponentially with the increase in ion flux (0 to 6.07 × 105 ions/cm2). Indirect optical band gap is found to decrease (4.118 to 3.917eV) linearly with the increase in ion flux (3.03×105 to 6.07×105 ions/cm2).

Structural and optical properties of CR-39 polymer implanted with laser produced plasma ions of iron

A passive Q-switched Nd:YAG pulsed laser was used to irradiate 99.99% pure Fe target in vacuum ~10−3Torr. The CR-39 specimens were exposed to laser produced plasma ions (40–250keV) emitted along the normal to the Fe target surface. The flux of Fe ions was varied by varying the number of laser shots in the range 500–1500 with an increment of 250. A comparison of structural and optical properties of CR-39 polymer before and after ion implantation was made. The increase in ion flux leads to the transformation of polymer into rather more disordered amorphous state leading to the broadening of XRD peaks. The crystallite size decreases (3.547 to 1.618nm) and Urbach energy increases (0.232 to 0.291eV) exponentially with the increase in ion flux (0 to 6.07×105 ions/cm2). Indirect optical band gap is found to decrease (4.118 to 3.917eV) linearly with the increase in ion flux (3.03×105 to 6.07×105 ions/cm2).

Analytical theory of charge-exchange-caused dips in spectral lines of He-like ions from laser-produced plasmas

Previously we discovered a way for producing not-yet-available fundamental data on charge exchange between multicharged ions, virtually inaccessible by other experimental methods. It was based on the formation of dips (called x-dips) in spectral lines of hydrogen-like ions from laser-produced plasmas. At that time the x-dip phenomenon was considered to be possible only in spectral lines of hydrogenic systems: due to the existence of exact algebraic (higher than geometrical) symmetries relevant only to hydrogenic systems and to the corresponding two-Coulomb-centre systems (dicentres) having one electron. In the present paper, by engaging the concept of an approximate algebraic symmetry of two-electron dicentres (and of helium-like ions), we opened up the way to significantly broaden the scope of experimental studies of the x-dip phenomenon—to studies of possible x-dips in spectral line profiles emitted by He-like ions in laser-produced plasmas. We identified three prospective two-electron dicentres and calculated analytically theoretical positions of the x-dips in the corresponding He-like spectral lines (though future experimental and theoretical studies should not be limited to these three two-electron dicentres). Since future experimental and theoretical studies should not be limited to these three two-electron dicentres, we presented also a table containing 15 prospective He-like spectral lines and 10 corresponding solid targets for observing x-dips in laser-produced plasmas. For completeness we presented also a similar table for H-like lines. It presented 16 prospective H-like spectral lines and 11 corresponding solid targets for observing x-dips in laser-produced plasmas. From the shape of experimental x-dips it is possible to determine the rate coefficient of charge exchange in the corresponding dicentre, as demonstrated previously. Therefore the results of the present paper should very significantly extend the range of fundamental data on charge exchange between multicharged ions that can be obtained via the x-dip phenomenon, but not by any other method.

Ion shock acceleration by large amplitude slow ion acoustic double layers in laser-produced plasmas

A kinetic model for the shock acceleration of ions in laser-produced plasmas is developed. A fraction of the warm ions are accelerated by the large amplitude monotonic potential of the shock created due the plasma compression and electron heating by the laser. The kinetic model for the monotonic shock is based on the slow ion acoustic double layer (SIADL). It is found that the amplitude of the large amplitude SIADL is almost uniquely defined by the electron temperature. Therefore, a balance between electron heating and plasma compression is needed for optimal ion acceleration by this scheme. Typical Mach numbers of the monotonic shocks are close to 1.5. The scheme could potentially produce monoenergetic ions with a relative energy spread of less than 1%. The model is compared with recent simulations and experiments, where efficient shocks acceleration and production of monoenergetic protons have been observed. Similarities and differences with other shock models are pointed out and discussed.

Application of General-Purpose Radiation Transport Code into Study for Laser-Produced Plasma Ions Acceleration

Application of General-Purpose Radiation Transport Code into Study for Laser-Produced Plasma Ions Acceleration

Measurements of electron-induced neutrons as a tool for determination of electron temperature of fast electrons in the task of optimization laser-produced plasma ions acceleration

High intensity laser-plasma interaction has attracted considerable interest for a number of years. The laser-plasma interaction is accompanied by generation of various charged particle beams, such as high-energy proton and ions with high charge to mass ratio (Q/M; same as multi-charged ions). Results of simultaneous novel measurements of electron-induced photonuclear neutrons (photoneutron), which are a diagnostic of the laser-plasma interaction, are proposed to use for optimization of the laser-plasma ion generation. The proposed method is demonstrated by the laser irradiation with the intensity of 1 × 10(21) W/cm(2) on the metal foil target. The photoneutrons are measured by using NE213 liquid scintillation detectors. Heavy-ion signal is registered with the CR-39 track detector simultaneously. The measured signals of the electron-induced photoneutrons are well reproduced by using the Particle and Heavy Ion Transport code System. The results obtained provide useful approach for analyzing the various laser based ion beams.

Characterization of laser-produced plasma ions of various metals and their effect on the optical properties of the CR-39 polymer

The laser-produced plasma (LPP) ions of various metals (Mo, Ni, Cu, Ti and Zn) was implanted in CR-39 polymer, and their influence on its optical properties was investigated. The plasma of these metals was produced using 200 shots of a Q-switched Nd:YAG pulsed laser in a vacuum of 10−3 Torr. The CR-39 specimens were exposed to LPP ions (flux: F=8.01×109−22.14×109 ions/m2, average energy: E av=52−297 keV) emitted along the normal to the metal surface in each case. Both F and E av were found to be a function of the room temperature Debye–Waller thermal parameter B and increase with increase in B-value. The structural behavior of virgin and implanted specimens was investigated using a ultra violet (UV)–visible spectrophotometer. The value of disorder content (Urbach energy E u) was found to lie in the range of 0.287–0.377 eV. The optical band gap energy (E g) for indirect transition decreased on implantation with metallic LPP ions, whereas such a variation in the case of direct transition was negligible. It was observed that E g for indirect transition increases with the increase in E u, whereas the dependence of E g for direct transition on E u was negligible.

Effect of light gas atom inclusions on the characteristics of laser-produced plasma ions

Using the mass-spectrometric method we studied the effect of light gas inclusions on the formation process of multi-component laser-induced plasma ions. Mass–charge characteristics, as well as energy and spatial distribution of the plasma ions are analysed. We found that both the energy and maximal charge of heavy component ions decrease due to the presence of gas atoms in the solid target surface layer.

Methods for improving characteristics of laser source of ions

In this work we discuss three methods to improve characteristics of laser source of ions, namely: (i) effect of the angle of interaction of laser radiation with targets on the plasma ions characteristics, (ii) the effect of target composition on the plasma ions, and (iii) influence of the repetition rate of laser pulses on plasma parameters. Our study will be based on the analysis of mass-charge spectrum of laser-produced plasma ions for different intensity of laser radiation.

Methods for improving characteristics of laser source of ions

In this work we discuss four methods to improve the characteristics of laser source of ions, namely: (i) the effect of the angle of interaction of laser radiation with targets on the plasma ions characteristics, (ii) the use of targets of different densities to improve the parameters of plasma ions, (iii) the influence of laser frequency on the plasma parameters and (iv) the effect of irradiation dose of the target on the emission of multi-charged ions. Our study will be based on the analysis of the mass-charge spectrum of laser-produced plasma ions for different intensities of laser radiation.

Aperiodic x-ray multilayer mirrors and their application in plasma spectroscopy

We discuss the potentialities of aperiodic multilayer structures for the reflection of XUV radiation, including attooptical applications. Pilot samples of aperiodic normal-incidence broadband focusing multilayer mirrors are employed in a stigmatic transmission grating spectrograph with an operating range of 12.5–30 nm.This spectrograph was used to study (i) the XUV spectra arising from the charge exchange of laser-produced plasma ions with rare-gas (Xe, Kr, He) jet atoms, (ii) a debris-free Xe-jet plasma XUV source driven by Nd-laser pulses.

Experimental discovery of charge-exchange-caused dips in spectral lines from laser-produced plasmas.

We report the first experimental observation of charge-exchange-caused dips (also called x dips) in spectral lines of multicharged ions in laser-produced plasmas. Specifically, in the process of a laser irradiation of targets made out of aluminum carbide, we observed two x dips in the Ly(gamma) line of Al XIII perturbed by fully stripped carbon. From the practical point of view, this opens up a way to experimentally produce not-yet-available fundamental data on charge exchange between multicharged ions, virtually inaccessible by other experimental methods. From the theoretical viewpoint, the results are important because the x dips are the only one signature of charge exchange in profiles of spectral lines emitted by plasmas and they are the only one quasimolecular phenomenon that could be observed at relatively "low" densities of laser-produced plasmas.

DETERMINATION OF ELECTRON TEMPERATURE IN LASER-PRODUCED PLASMAS BY ISOELECTRONIC XRAY SPECTROSCOPY

Experiments were performed to determine the electron temperatures of Mg/Al disk target and gold disk target mixed with tracing Mg/Al materials irradiated by laser beams at a wavelength of 0.35μm from the “Xing Guang Ⅱ”high-power laser facility.X-ray spectra from the targets were measured by a crystal spectrometer.The technique of multi-configuration Dirac-Fock was used to calculate relevant atomic parameters.Variations of relative intensity of isoelectronic lines from the two tracing ions in laser-produced plasmas with the electron temperature were derived according to local-thermodynamic-equilibrium model.Based on the above-mentioned experiment the electron temperatures of the plasmas generated by focusing laser pulse on the targets were determined via isoelectronic line ratios.

Multiple reflections in single crystals as a tool for X-ray spectroscopy

The process of multiple x-ray reflections in single crystals is presented as a tool for x-ray spectroscopy. Among the possible applications it is shown that monochromatic spatial resolution of the x-ray source may be obtained through this process. With this method the distribution of variously ionized ions in laser-produced plasmas may be determined. Absolute wavelength values of x-ray transitions can be obtained. The x-ray emission qualities of x-ray tubes can be determined.