Results 1 - 10 of 39
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[en] In this paper, experimental results are presented for the spatial and energy distributions of charge-discriminated Sn ions ejected from laser-produced plasmas. The plasmas were formed on solid, planar Sn targets, irradiated with a Nd:YAG laser. Ions were investigated using a calibrated electrostatic sector analyzer, scanning an energy-to-charge ratio range of 0.22 to 2.2 keV/e for emission angles between 20 and 80 degrees relative to target normal. Results were obtained for three laser power densities, in the region suitable for inducing significant extreme ultraviolet emission, of the order 1.5-8.1 x 1011 W/cm2. The fully differentiated data were found to be well characterized by Gaussian fits, which allowed trends in the emission profiles to be readily quantified. Ions of set energy and charge were observed to possess a preferential angle of emission, the superposition of which yields a physical basis for the total angular emission observed previously and in this work. The experimental results obtained have been related to physical processes within the plasma that influence the energy and angle of ejection of ions from laser produced plasmas.
[en] A new technique for measuring electron impact ionisation cross-sections using an EBIT is presented. The method involves determining the charge distribution of ions extracted from the trap after well defined confinement times. Analysis of the onsets for the appearance of particular charge states in the trap gives ionisation rates which may be converted, under appropriate conditions, to relative cross-sections without theoretical input. The method has been used to make measurements for Ar15+, Ar16+ and Ar17+. (author)
[en] Rotationally selective vibrational autoionization in molecular hydrogen has been investigated using two-dimensional photoelectron spectroscopy. Measurements of electron yield as a function of both electron and photon energy have been carried out using tuneable synchrotron VUV radiation between the υ = 0 and υ = 1 vibrational thresholds of H2+ X 2Σg+, 15.45-15.70 eV. Constant rotational transition energy spectra have been extracted revealing the decay routes of autoionizing states. No large changes in the rotational quantum number of the ion core during autoionization were observed. (author)
[en] The autoionizing decay routes of doubly excited, 1Po, Rydberg states in helium have been investigated using two-dimensional photoelectron spectroscopy. Constant ionic state spectra for the He+ (N = 4, 5 and 6) states have been extracted from two-dimensional photoelectron spectra obtained in the photon energy region 75.5-79 eV. A preference was observed for autoionizing decays in which the change in the principle quantum number, N, of the electron which remains bound was minimized. This is in accordance with propensity rules determined from theoretical studies. The energies of the lower members of the most prominent Rydberg series (N, N -2n) converging on each of the He+ (N = 5) and He+ (N = 6) thresholds have been determined. (author)
[en] Angularly and rotationally resolved measurements of photoelectron angular distributions for the X2Σg+(ν+=0, N+=0) ground state of para-H2+ are presented, over the photon energy range, 15.47-15.75 eV. This range includes most of the autoionising resonances that decay primarily into the ground vibrational ionic state. The measurements were performed using synchrotron radiation, a high-resolution hemispherical analyser and a magnetic angle changer. The value of the asymmetry parameter in this energy interval is close to 2, but sharp variations are observed at particular photon energies
[en] Resonant triple-differential cross-section (TDCS) measurements were performed on atomic strontium on the 4p → 4d resonance. A variety of energy sharings were examined with the experimental arrangement in the coplanar geometry. The angle of detection of one electron, relative to the direction of the E-vector vector of the fully linear polarized incident photon beam, was set to -90 deg. The mutual angle between the two electrons had a range just short of 90 deg. → 270 deg. These experimental data are presented with comparisons made to similar data from West et al (2001 J. Phys. B: At. Mol. Phys. 34 4169-81) and to the theoretical characterization as derived by Malegat et al (1997 J. Phys. B: At. Mol. Phys. 30 251-61) using the parametrization of Cvejanovic and Reddish (2000 J. Phys. B: At. Mol. Phys. 33 4691-709). All of the present TDCS measurements display unexpected lobes at a mutual emission angle of 180 deg, possible explanations for these lobes are explored
[en] Efficiency optimization of a stable and debris free plasma source at 13.5 nm, is at the forefront of current extreme ultraviolet lithographic (EUVL) research efforts. To date, 1-2.5% soft x-ray conversion efficiencies (CEs) within a 2% bandwidth (BW) around 13.5 nm and into 2π steradians have been attained experimentally for laser-produced plasmas containing Sn at power densities of 0.5-5 x 1011 W cm-2. In order to complement these experimental endeavours, we have undertaken to study the CE, for the given wavelength regime, in the optically thick limit. We have achieved this by coupling time-dependent and steady-state collisional-radiative (CR) equations to the output of the one-dimensional hydrodynamic code MED103 (MEDUSA), where a solid sphere of radius 50 μm was uniformly irradiated by a high intensity laser pulse with a Gaussian temporal profile. The ion populations obtained from these CR results were then used in an integrated spatio-temporal figure of merit (FOM) together with in-band weighted dipole oscillator strengths and transition energies. The maximum FOM, when divided by the laser energy, was found to occur in the range of peak power densities of 2-3 x 1011 W cm-2 for the steady-state and time-dependent models, respectively. The hydrodynamic variables of these peak power densities were then used in a radiative transfer calculation in which the many-celled spherical plasma was treated as a multi-component blackbody. It is found that CEs of 3.5-6% within the 2% BW per 2π steradians may be achieved. These results are of particular relevance to EUVL technologies where a minimum CE of 3% is required by industry
[en] The charge state and energy distributions of ions emitted from a Sn-based laser-produced plasma extreme ultraviolet source, formed at a power density of ∼4 x 1011 W cm-2, have been recorded as a function of angle. Measurements were recorded from 20 deg. to 80 deg. with respect to the target normal. For each individual ion stage detected, more energetic ions showed preferential emission close to the target normal whereas the less energetic ions exhibited peak emission at larger angles. The peak in the observed ion emission moved to higher energies with increasing ionization at all angles. The sum of the emission, for each ion stage recorded, at each observed kinetic energy, decreased with increasing angle from the target normal.
[en] In this work ions emitted from a laser produced plasma created from a solid tin target have been analyzed using a spherical sector energy analyzer (ESA). Employing time of flight analysis, the ESA allows determination of ion energy and charge stage as a function of ion emission angle. Ions of charge Sn+1 - Sn+9 with energy to charge ratios of 0.22 - 3.2keV have been investigated over a range of emission angles from 20 - 80 degrees, relative to the target normal, for three distinct laser pulse energies
[en] Resonant triple-differential cross-section (TDCS) measurements on atomic strontium on the 4p → 4d resonance are presented. All of these TDCS measurements display unexpected lobes at a mutual emission angle for the two electrons of 180o. Possible explanations for these lobes are explored.