XUV spectra of 150 ps laser-produced samarium (Sm) plasmas in the 1.8-10 nm wavelength region, where Δn=1, n=4−n=5 and Δn=0, n=4−n=4 transitions dominate the observed emission, were investigated experimentally and theoretically. Ab initio calculations using the flexible atomic code, as well as consideration of isoelectronic trends, are all employed to identify a number of new features in spectra from Sm 16+ to Sm 34+ . The results show that Δn=0, n=4−n=4 emission from highly charged ions merge to form an intense unresolved transition arrays in the 7.5 nm region and Δn=1, n=4−n=5 resonance transitions contribute in the 3-7 nm region of the Sm spectrum. In addition, a number of strong individual lines at shorter wavelengths are seen to arise from Cu-and Zn-like ions and a number of new assignments are made for Zn-like Sm 32+ .
The effects of shape and thickness of a tin surface layer and of the energy of a 170 ps neodymium:yttrium-aluminum-garnet laser pulse on the conversion efficiency (CE) into extreme ultraviolet emission in the 13.5 nm region is investigated. Whereas a CE of up to 1.16% into the 2% reflection band of multilayer Mo/Si optics was measured for a bulk Sn target at a laser energy of 25 mJ, significant CE enhancement up to 1.49% is demonstrated for a 200-nm-thick Sn layer on a microstructured porous alumina substrate.
The soft x-ray emission spectra of femtosecond-laser-produced plasmas from 2nd row transition elements from yttrium (Z = 39) to palladium (Z = 46), with the exception of technetium (Z = 43), were measured in the 1–5 nm region. Plasmas were produced by shining pulses from a titanium–sapphire laser with 65 fs pulse duration and an energy per pulse of 4.5 mJ focused to an intensity of 3 × 1015 W cm−2 onto bulk targets. While the emission spectra from yttrium to molybdenum (Z = 42) contain only the unresolved transition arrays (UTA) already observed in nanosecond and picosecond laser-target interactions described in our previous paper (Lokasani et al 2015 J. Phys. B: At. Mol. Opt. Phys.
48 245009), transitions from higher ionization states are clearly demonstrated in the spectra emitted from ruthenium (Z = 44), rhodium (Z = 45) and palladium targets heated by the femtosecond laser. These UTAs are interpreted by comparing the experimental spectra to calculated results, obtained using the Cowan suite of codes, the flexible atomic code as well as previous predictions of isoelectronic trends. The 3d–4f transitions arrays emitted from Ru XXI-XXIII, Rh XXI-XXIII and Pd XXI-XXIII ions are clearly seen in the observed spectra. To our knowledge, such high ionization states are demonstrated for the first time at such moderate laser energies.
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