Dual Laser Plasma Research Articles

Application of a picosecond laser plasma continuum light source to a dual-laser plasma photoabsorption experiment

The characteristics of an extreme-ultraviolet (XUV) continuum light source and its application to a dual-laser plasma (DLP) photoabsorption experiment are described. The continuum emitting plasma was formed by focusing a 7 ps, 248 nm, 15 mJ laser pulse onto a number of selected targets known to be good XUV continuum emitters (Sm, W, Au and Pb), while the second absorbing plasma was produced by a 15 ns, 1064 nm, 300 mJ pulse. The duration of the continuum emission for these plasmas has a mean value of ~150 ps, but depends on both the target material and the picosecond laser pulse energy. Using this picosecond DLP set-up we have been able to measure the photoabsorption spectrum of an actinide ion (thorium) for the first time.

Absolute photoionization cross section of K+ ions from the 3p to the 3s threshold

The absolute photoionization cross section of ground state K+ ions has been measured from the 3p threshold to above the 3s threshold (31-49 eV) by VUV radiation using a merged ion-photon beam set-up. The cross section, which reaches a maximum value of 32 Mb ±10% at 31.8 eV and then decreases with energy, is in overall good agreement with absolute measurements by Peart and Lyon, but the present investigation also reveals the 3s3p6np 2P (n = 4-6) resonances and eliminates a previously unassigned structure at 35.5 eV. The energies, widths and shape parameters of the autoionizing 2P resonances are determined and compared with recent data from dual-laser plasma measurements and with theoretical predictions. The present experimental set-up will allow absolute photoionization cross sections 0.1 Mb to be measured, making it possible to measure the absolute photoionization cross sections of ions of astrophysical importance.

New dual laser plasma investigations of inner-shell excitations

Abstract Absorption spectroscopy of laser plasma plumes with XUV continuum radiation from a second laser-produced plasma generated on a high atomic number target provides a flexible approach to the study of inner-shell and multiple-electron excitations in atoms and ions. This technique, termed the Dual Laser Plasma (DLP) photoabsorption technique, is applied here to generate new data for: 2s inner-shell excitations in neutral neon, Na + and Mg 2+ ; 2p photoabsorption in neutral silicon; and 3p photoabsorption in Cr 2+ . Some preliminary interpretative results based on detailed Cowan code calculations are also presented.

Absorption spectroscopy of an expanding laser produced lithium plasma in the extreme ultraviolet using the Dual Laser Plasma technique

We describe the essential features of the Dual Laser Plasma (DLP) vacuum ultraviolet photoabsorption spectroscopy technique and the characteristics of our DLP apparatus. We show that the time- and space-resolved capabilities of this technique are suited to the monitoring of the dynamics of expanding plasma plumes in the regime used for pulsed laser deposition of materials. Examples of spectra showing the spatial and temporal evolution of a lithium plasma expanding in vacuum are presented. A model based on a self-similar expansion for the plume is developed and used to analyse the shape of absorption lines. Measurements in the photoionisation continuum of Li + are also presented.

3d Photoabsorption in Zn II, Ga III and Ge IV

The 3d photoabsorption spectra of Cu I-like Zn II, Ga III and Ge IV have been recorded in the 25-100 eV region using the dual laser plasma technique. The spectra are dominated by transitions of the type which have been identified by comparison with multiconfiguration Hartree-Fock calculations.

Measurement and analysis of the photoabsorption spectra of laser-produced Al and in the region of 2p-subshell excitation

The 2p-subshell photoabsorption spectra of atomic aluminium and singly ionized silicon, measured using the dual-laser plasma technique, are presented. The spectra are dominated by and one- and two-electron excitations, respectively. Relative photoabsorption cross sections, derived from the experimental spectra, are compared with computed theoretical cross sections. An interpretation is provided within the framework of the Hartree-Fock configuration-interaction calculations. It is found that mixing between core singly and doubly excited configurations strengthens with increasing atomic number at the beginning of the aluminium isoelectronic sequence. This observation is in contrast to our findings for the Mg-like isoelectronic species Mg, and (Sayyad M H et al 1995 J. Phys. B: At. Mol. Opt. Phys. 28 1715) in which such mixing weakens with increasing atomic number.

Measurement of the XUV photoabsorption spectra of atomic zinc and its ions : n = 1, 2, and 3 in the region of 3p-subshell excitation

Photoabsorption studies, using the dual laser plasma technique, have been initiated along the zinc isonuclear sequence as far as in the energy region corresponding to 3p-subshell electron excitation. For neutral, singly and doubly ionized zinc the 3d-subshell remains closed and excitations of the type 3p - ns have been found to predominate. The symmetric nature of the resonance profiles is evidence of the weak interaction of these discrete states with the underlying continua. The relatively large widths of the resonances can be interpreted as being mostly due to the nonradiative decay of the 3p core hole through both super and normal Coster - Kronig decay processes. The spectral signature of the `transition metal-like' 3p - 3d resonance is dramatically different, the asymmetric nature of which reflects the increased interaction between direct 3d photoionization and the discrete excitation processes. The main resonances in the spectra of , and have been parametrized and compared with calculations based on both single-particle and collective models.

Infrared Spectroscopy of the C4 Anion: Reassignment of the 1699.8 cm-1 Band

Using a newly developed dual beam laser plasma method, the C4- anion cluster has been formed and deposited in an argon matrix and studied via Fourier transform infrared spectroscopy. An infrared band at 1699.8 cm-1, previously assigned to a combination mode of the neutral C4 cluster, is shown to be due to the asymmetric stretching fundamental of the C4- anion. This attribution is based on the different behavior of the known 1543.4 cm-1 neutral C4 asymmetric stretching mode and the 1699.8 cm-1 band under action of annealing, photolysis, and addition of the electron trap, CCl4, to the plasma gas. Density functional theory and ab initio theory calculations predict a stable, linear C4 anionic cluster that should possess a moderately strong IR band close to this position. Previous isotopic (12C/13C) splitting patterns are reinterpreted and shown to match very well with the theoretically predicted splitting patterns for C4-. An electron photodetachment energy of 4.51 eV is found and compares well with the gas-phase value when account is taken of the matrix stabilization energy of 0.63 eV. It is proposed that anions are formed via electron capture by preformed neutral C4 clusters and that a steady state of neutral and anionic C4 clusters is established in the matrix.

The 3p photoabsorption spectra of K II and Ca III

The 3p photoabsorption spectra of K II and Ca III have been recorded in the 25-55 eV region using the dual laser plasma technique. With the help of calculations performed with the Cowan code and Rydberg series expansions, many 3p to ns, d transitions have been identified in these ions. Strong LS-term-dependent behaviour arising from 3d wavefunction contraction is seen to influence intensities and quantum defects in the 3p to nd series.

2p-subshell photoabsorption by Si2+ ions in a laser-produced plasma

The 2p-subshell photoabsorption spectrum of Mg-like silicon has been recorded for the first time using the dual laser plasma (DLP) technique. The spectrum is discussed within a framework of the evolution of 2p photoabsorption along the Mg-like isoelectronic sequence. Assignments of the Si2+ spectrum based on Hartree-Fock configuration interaction (HFCI) calculations are presented.

4f(1P) giant dipole resonance in La3+

Photoabsorption of free ${\mathrm{La}}^{3+}$ ions in the $4d$ excitation region has been measured using the dual-laser plasma technique. A dramatic strong and broad ${4d}^{9}4f{(}^{1}P)$ giant dipole resonance was observed. The interpretation of the results is provided using theoretical techniques which go beyond the independent particle approximation. In particular the strong term dependence for $4f{(}^{1}P)$ gives evidence of strong polarization effects for the description of the giant dipole resonance.

XUV photoabsorption of laser generated Au vapour

Photoabsorption by atomic Au in the 5p and 4f excitation region has been studied using the dual laser plasma (DLP) technique. The observed features are dominated by two prominent Fano-type resonance lines which can be attributed to 5p to 5d and 4f to 5d transitions of valence excited 5d96s2(2D52/) Au followed by autoionization. The experimental results are compared to spectra calculated for the excitation of 5d106s1(2S12/) ground and 5d96s2(2D52/, 2D32/) valence-excited states within the (R)Hartree-Fock theory and the relativistic time dependent local density approximation.

First observation of a photon-induced triply excited state in atomic lithium.

Using a dual laser plasma technique we have measured for the first time the photoabsorption spectrum of atomic lithium at energies corresponding to the simultaneous excitation of both 1s electrons. We have observed the main triply excited 1${\mathit{s}}^{2}$2s${(}^{2}$S)\ensuremath{\rightarrow}2${\mathit{s}}^{2}$p${(}^{2}$P) transition with Fano parameters ${\mathit{E}}_{0}$=142.32\ifmmode\pm\else\textpm\fi{}0.05 eV \ensuremath{\Gamma}=0.20\ifmmode\pm\else\textpm\fi{}0.04 eV, and q=-2.2\ifmmode\pm\else\textpm\fi{}0.6. Our experiment represents the first step in photoionization studies of this fundamental atomic system in which the motion of the three electrons in the field of the nucleus is so highly correlated.

XUV photoabsorption of laser-generated W and Pt vapours

The absorption spectra of atomic W and Pt have been recorded by the dual laser plasma technique in the range of the 4f and 5p excitations. Broad, strong and asymmetric 5p to 5d resonances dominate the spectra. The Pt 4f to 5d transitions give rise to prominent maxima superimposed on the high energy slope of the 5p to 5d resonances. Strong coupling to the 5d to in f continuum manifests itself in the asymmetric profiles of the resonances and the extremely low cross section below the 5p onset for atomic W. The experimental results are compared to spectra calculated within the many-body perturbation theory and the relativistic random-phase approximation.

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.

LOW LYING ODD PARITY AUTOIONISING STATES IN THE 2p-SUBSHELL ABSORPTION SPECTRUM OF A1 III AND Si IV

The photoabsorption spectrum of an aluminum plasma and of a silicon plasma were photographed in the E W region. The absorption technique used utilises two laser plasmas, one produces the background continuum, the other generates the absorbing medium. Under appropriate experimental conditions the 2p-subshell excitation spectra of the sodium-like ions ARIII and Si IV were observed. The observed spectra are interpreted with the help of multiconfiguration Dirac-Fock type calculations. The study of photoabsorption spectra of atoms and ions provide valuable information relevant to several different areas such as astrophysics or short wavelength laser studies for example. For purpose of systematising, absorption studies should ideally be carried out over extended isoelectronic and isonuclear sequences. However, when using conventional atomic or ionic absorption techniques, one encounters severe difficulties obtaining the spectra of highly refractory and/or corrosive elements in the vapor phase and also the spectra of multiply charged ions. The dual laser-plasma absorption technique1 presents some advantages that overcome these difficulties. The latest development based on this techniquez is characterised by a great versatility which allows time resolved absorption studies over a wide range of ionisation stages as well as neutral species. In this paper we present wavelength measurements of inner-shell transitions in the sodium-like ions ARIII and SiIV. The corresponding spectra are due to the excitation of a 2p-subshell electron into outer shells. Similar studies were carried out in NaI by several groups over the past years 3*4 s5 and In MgII by Esteva and Mehlman6. In the following, we will first describe briefly the experimental technique used, outline the main features of the 2p spectrum of Na-like species, and then present and comment on our results. The experimental technique consisted of equally dividing the output of a 1.55, 30 nanos., Q-switched ruby laser between a cylindrical lens and a spherical lens combination. Two different solid targets in vacuo were positioned at the foci such that a line plasma was formed at the surface of one and a point plasma at the surface of the other. The line plasma (aluminium or silicon) constituted the absorbing medium, the point plasma (tungsten or hafnium) acted as a source of quasi Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1987934