Bright narrow band emission observed in optically thin plasmas of high-Z elements in the extreme ultraviolet spectral region follows a quasi-Moseley's law. The peak wavelength can be expressed as λ=(21.86±12.09)×R∞−1×(Z−(23.23±2.87))−(1.52±0.12), where R∞ is the Rydberg constant. The wavelength varies from 13.5 nm to 4.0 nm as the atomic number, Z, increases from Z = 50 to Z = 83. The range of emission wavelengths available from hot optically thin plasmas permits the development of bright laboratory-scale sources for applications including x-ray microscopy and x-ray absorption fine structure determination.

Extreme ultraviolet spectra of highly-charged rhenium ions were observed in the 1–7 nm region using two Nd:YAG lasers with pulse lengths of 150 ps and 10 ns, respectively, operating at a number of laser power densities. The maximum focused peak power density was 2.6 × 1014 W cm−2 for the former and 5.5 × 1012 W cm−2 for the latter. The Cowan suite of atomic structure codes and unresolved transition array (UTA) approach were used to calculate and interpret the emission properties of the different spectra obtained. The results show that n = 4-n = 4 and n = 4-n = 5 UTAs lead to two intense quasi-continuous emission bands in the 4.3–6.3 nm and 1.5–4.3 nm spectral regions. As a result of the different ion stage distributions in the plasmas induced by ps and ns laser irradiation the 1.5–4.3 nm UTA peak moves to shorter wavelength in the ps laser produced plasma spectra. For the ns spectrum, the most populated ion stage during the lifetime of this plasma that could be identified from the n = 4-n = 5 transitions was Re23+ while for the ps plasma the presence of significantly higher stages was demonstrated. For the n = 4-n = 4 4p64dN-4p54dN+1 + 4p64dN−14f transitions, the 4d-4f transitions contribute mainly in the most intense 4.7–5.5 nm region while the 4p-4d subgroup gives rise to a weaker feature in the 4.3–4.7 nm region. A number of previously unidentified spectral features produced by n = 4-n = 5 transitions in the spectra of Re XVI to Re XXXIX are identified.

We demonstrate efficient enhancement of soft X-ray (SXR) emission from molybdenum plasmas produced using dual pulse irradiation, in which 10-ns and 150-ps pre-pulses were followed by a 150-ps main pulse. The number of photons was observed to be 5.3 × 1016 photons/sr, which corresponded to a conversion efficiency of 1.5%/sr in λ = 2.34–4.38 nm region at a pulse separation time of 1 ns with the 150-ps pre-pulse. The conversion efficiency became 1.3 times as large as that produced by a single pulse. The results indicate the advantage of dual pulse irradiation using sub-ns pre-and main pulses to produce the bright plasmas required for applications such as laboratory based SXR microscopy.

The unresolved transition arrays (UTAs) emitted from laser produced bismuth (Bi) plasma sources show potential for single-shot live cell imaging. We have measured extreme ultraviolet spectra from bismuth laser produced plasmas in the 1–7 nm region using a λ = 1064 nm Nd:YAG laser with a pulse duration of 150 ps. Comparison of spectra obtained under different laser power densities with calculations using the Hartree–Fock with configuration interaction Cowan suite of codes and the UTA formalism, as well as consideration of previous predictions of isoelectronic trends, are employed to identify lines and a number of new features in spectra from Bi XXIII to Bi XLVII. The results show that Δn = 0, n = 4–4 emission from highly charged ions merges to form intense UTAs in the 4 nm region and Δn = 1, n = 4–5 resonance transitions UTAs dominate the 1–3 nm region of the Bi spectrum.

No abstract