Dual Laser-produced Plasma Research Articles

Charge-separated spectra of suprathermal highly charged bismuth ions in a dual laser-produced plasma soft x-ray source.

We investigated the charge-separated spectra of highly charged suprathermal bismuth (Bi) ions from a dual laser-produced plasma soft x-ray source developed for soft x-ray microscopy. The charge distribution of these suprathermal ions emitted from a solid planar Bi target was measured by an electrostatic energy analyzer. The maximum ionic charge state was observed to be Z = 17 and to possess a maximum energy of about 200 keV. This evaluation provides important information essential for the development of debris mitigation schemes in a soft x-ray microscope.

Theoretical Analysis of 4f and 5p Inner-Shell Excitations of W-W3+ Ions

Detailed theoretical calculations are performed for the 4f and 5p inner-shell excitations of W-W3+ ions using the multiconfiguration Hartree—Fock method in order to better understand the origin of the XUV photoabsorption spectra of W atoms from the dual laser-produced plasma experiment (Costello et al. J. Phys. B 24 (1991) 5063) and the spectra of photon-induced single ionization of Wq+ ions (q = 1, 2, 3) (Müller et al. Phys. Scr. T144 (2011) 014052) from photon-ions merged beam experiments, respectively. Two broad and strong resonances in the experimental spectra have also been theoretically identified mainly from 5p–5d resonance. The 4f–5d, 6d and 5p–6d transitions also make a small contribution to each spectrum, which are superimposed on the 5p–5d transition arrays. Based on the assumption of a normalized Boltzmann distribution among the excited states, we succeed in reproducing spectra which are in good agreement with experiments.

Analysis of the xuv photoabsorption spectrum ofAu2+,Au3+, andAu4+

The photoabsorption processes of ${\text{Au}}^{2+}$, ${\text{Au}}^{3+}$, and ${\text{Au}}^{4+}$ have been investigated experimentally and theoretically in the 70--127 eV region. Using the dual laser-produced plasma technique, the $4f$ and $5p$ photoabsorption spectrum has been recorded at 50 ns time delay and was found to be dominated by a great number of lines from $4f\text{\ensuremath{-}}5d$, $6d$ and $5p\text{\ensuremath{-}}5d$, $6s$ transitions, which have been identified by comparison with the aid of Hartree-Fock with configuration interaction calculations. The characteristic feature of the spectrum is that satellite lines from excited configurations containing one or two $6s$ electrons are more important than resonance lines, and with increasing ionization, satellite contributions from states with one $6s$ spectator electron gradually become more important than those with two $6s$ spectator electrons. Based on the assumption of a normalized Boltzmann distribution among the excited states and a steady-state collisional-radiative model, we succeeded in reproducing a spectrum which is in good agreement with experiment.

Absolute photoionization cross-section measurements of the Kr I isoelectronic sequence

Photoionization spectra have been recorded in the $4s$, $4p$, and $3d$ resonance regions for the Kr I isoelectronic sequence using both the dual laser produced plasma (DLP) technique (at DCU) to produce photoabsorption spectra, and the merged ion beam and synchrotron radiation technique (at ASTRID) to measure absolute photoionization cross sections. Profile parameters are compared for the $4s\text{\ensuremath{-}}np$ resonances of ${\mathrm{Rb}}^{+}$ and ${\mathrm{Sr}}^{2+}$. Many $4p\ensuremath{\rightarrow}ns$, $md$ transitions are identified with the aid of Hartree-Fock calculations, and consistent quantum defects are observed for the various $ns$ and $md$ Rydberg series. Absolute single and double photoionization cross sections recorded in the $3d$ region for ${\mathrm{Rb}}^{+}$ and ${\mathrm{Sr}}^{2+}$ ions show preferential decay via double photoionization. This is only the second report to our knowledge where both the DLP technique and the merged-beam technique have been used simultaneously to record photoionization spectra, and the advantages of both techniques (i.e., better resolution in the case of DLP and values for absolute photoionization cross sections in the case of the merged-beam technique) are highlighted.

4d photoabsorption spectra of Sn II and Sn IV in the 30–65 eV region

EUV photoabsorption spectra of tin ions Sn II and Sn IV have been recorded using the dual laser-produced plasma (DLP) technique in the 30–65 eV region. It is known from previous studies by Lysaght et al (2005 Phys. Rev. A 72 014502), in the 30–100 eV domain, that gradual 4f contraction along the isonuclear sequence of Sn I through Sn IV results in a redistribution of the oscillator strength from the continuum to the pseudo-discrete 4d → f channels, with many intense absorption lines dominating the spectra of Sn IV. Using Hartree–Fock with configuration interaction calculations allows us to successfully account for, and permits identification of, pseudo-discrete 4d → np, nf features within the spectra of Sn II and Sn IV.

Photoionisation cross sections of atomic ions

Experimental techniques for photoionisation measurements on atomic ions are described, and recent progress in the measurement of absolute photoionisation cross sections is reviewed. The complementary contributions of the two main experimental methods, merged beam and dual laser produced plasma (DLPP), pointing out both the problems and advantages of the two different techniques, are discussed. Examples are given where absolute measurements have helped to resolve uncertainties in earlier experiments, together with the assistance of theoretical calculations. Future developments are indicated, particularly in the areas of multiply charged ions and negative ions.

Discrete structure in the 4d photoabsorption spectra ofCs III, Cs IV and Cs V

XUV photoabsorption spectra of caesium, in ion stages up to Cs4+, have been obtained experimentally with the dual laser-produced plasma technique. From the results it can be inferredthat the 4d photoabsorption cross-section changes dramaticallyin appearance along the isonuclear sequence Cs throughCs4+. While the spectra of Cs, Cs+ and Cs2+ aredominated by a giant dipole 4d →εfresonance, discrete structure, which essentially increases inintensity with increasing ion stage, is also present below threshold. Between Cs2+ and Cs3+ much of the oscillator strength is abruptly transferred from the continuumto the discrete spectrum so that a few intense broad featuresdominate the spectra of Cs3+ and Cs4+. Multiconfiguration Hartree-Fock calculations successfullyaccount for this behaviour and permit identification of thediscrete features.

The evolution of 4d photoabsorption in Sb with increasing ionization

The photoabsorption spectra of Sb+, Sb2+, Sb3+ and Sb4+ have been obtained in the XUV spectral region with the dual laser-produced plasma (DLP) technique. Photoexcitation from the 4d subshell is the dominant process in the 30-100 eV energy region. In Sb+, for photon energies between 30 and 50 eV, discrete structure corresponding to 4d np, n1f (n5,n14) transitions is obtained, while above 50 eV the spectrum is dominated by an intense 4df resonance. Apart from the 4d5p transitions the features are very weak. The 4df resonance is still observed in Sb2+ as the dominant feature in the spectrum, but in Sb3+ and Sb4+ there is significant transfer of oscillator strength from the continuum to the discrete spectra, in particular to the 4d nf transitions. This behaviour mirrors the effects of contraction of the 4f wavefunction, which is seen to be more gradual here than in elements with Z>54. Multiconfiguration Hartree-Fock and time-dependent local density approximation calculations successfully reproduce this behaviour.

Discrete structure in the 4d photoabsorption spectrum of

The photoabsorption spectrum of Xe-like has been obtained in the XUV spectral region with the dual-laser-produced plasma (DLP) technique. Photoexcitation from the 4d subshell is the dominant process in the 80 - 150 eV energy range and is intermediate in behaviour between the well documented cases of Xe and . Between 80 and 90 eV discrete structure, corresponding to transitions is obtained, while above 90 eV the spectrum is dominated by an intense resonance. Multiconfiguration Hartree - Fock (MCHF) calculations facilitated identification of the majority of the features observed.

Trends in 4d-subshell photoabsorption along the iodine isonuclear sequence: I, I+, and I2+

The 4d absorption spectra of I, ${\mathrm{I}}^{+}$, and ${\mathrm{I}}^{2+}$ have been observed in the 45--300-eV region using the dual laser-produced plasma technique. At lower energies each spectrum is dominated by intense 4d\ensuremath{\rightarrow}5p transitions, which are identified with the aid of multiconfiguration Hartree-Fock calculations. The excited states decay by direct autoionization involving 5s or 5p electrons and rates for the different processes and resulting linewidths were calculated and compared, where possible, with experiment. In the case of neutral iodine 4d\ensuremath{\rightarrow}6p transitions are also observed in the region close to the $^{2}$${\mathit{D}}_{5/2}$ threshold. The dominant feature in each spectrum, however, arises from 4d-f excitation, which evolves from a 4d-\ensuremath{\varepsilon}f shape resonance in neutral iodine to a feature containing discrete 4d\ensuremath{\rightarrow}nf transitions in ${\mathrm{I}}^{2+}$. \textcopyright{} 1996 The American Physical Society.

The M-shell photoabsorption spectrum of Ge2+

The dual laser produced plasma (DLP) technique, has been used to study the EUV absorption spectra of germanium plasmas in the 50-400 AA region. The absorbing plasmas were produced by focusing the output of a Q-switched ruby laser onto a germanium target while the background continuum was produced by focusing the output of a Nd:YAG oscillator/amplifier system onto a samarium target. At a time delay of 50 ns and an absorbing plasma column length of 2 mm the spectrum recorded was predominantly due to Ge2+. We have investigated 3d and 3p sub-valence transitions. In the former, 3d104s2 to 3d94s2nf and 3d94s2np series converging on the 2D5/2 and 2D3/2 limits of Ge3+ were identified by isoelectronic comparison and Hartree-Fock calculations. In the 3p case no strong line transitions were observed which was shown by many body calculations to result from line broadening caused primarily by super Coster-Kronig decay of the 3p hole.

3d absorption spectra of Sr I through Sr IV.

The extreme ultraviolet photoabsorption spectra of neutral to three-times-ionized strontium have been recorded in a comprehensive series of experiments with the dual laser-produced plasma technique. Striking differences were found in the spectra, which can be attributed to the transfer of oscillator strength from 3d\ensuremath{\rightarrow}np to 3d\ensuremath{\rightarrow}nf transitions at ${\mathrm{Sr}}^{2+}$ due to nf wave-function contraction. In Sr and ${\mathrm{Sr}}^{+}$, 3d\ensuremath{\rightarrow}5p transitions dominate; in ${\mathrm{Sr}}^{2+}$, 3d\ensuremath{\rightarrow}nf transitions are most intense, while in ${\mathrm{Sr}}^{3+}$ the 4p subshell opens and 3d\ensuremath{\rightarrow}4p transitions are the strongest features. Partial cross sections for 3d\ensuremath{\rightarrow}\ensuremath{\varepsilon}f and 3d\ensuremath{\rightarrow}\ensuremath{\varepsilon}p photoionization were calculated and compared with experiment.

Even-parity autoionizing states in the extreme-ultraviolet photoabsorption spectra of Mg, Al+, and Si2+

The dual-laser-produced plasma (DLP) photoabsorption technique has been used to study 2p\ensuremath{\rightarrow}3s excitations in the isoelectronic species Mg, ${\mathrm{Al}}^{+}$, and ${\mathrm{Si}}^{2+}$ prepared in the excited configuration 2${\mathit{p}}^{6}$3s3p. The autoionizing upper states belong to the 2${\mathit{p}}^{5}$3${\mathit{s}}^{2}$3p even-parity configuration. The versatility of the technique is demonstrated through a careful combination of space- and time-resolved photoabsorption scans. Plasma conditions optimized for the observation of the inaccessible parity regime were successfully reproduced along the isoelectronic sequence of interest. All the observed transitions were interpreted with the help of multiconfigurational atomic structure calculations. In the case of magnesium, the photoabsorption data are compared with the ejected-electron spectra excited by low-energy electron impact of Pejcev et al. [J. Phys. B 10, 2389 (1977)].

Ultraviolet Absorption of Refractory Elements by a Dual Laser Plasma Method

AbstractThe dual laser-produced plasma technique for the study of ionic absorption spectra has been developed by the use of two Q-switched ruby lasers to enable independent generation of the absorbing and back-lighting plasmas. Optical pulse handling is used in the coupling cicuits to enable reproducible pulse delays from 250 nsec. to 10 msec, to be achieved. At delay times > 700 nsec. spectra of essentially pure neutral species are observed. The technique is valuable, not only for obtaining the neutral spectra of highly refractory and/or corrosive materials but also for studying behaviour of ionic species as a function of time. Typical spectra are shown in Fig. 1.