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The identification of sources for applications that include nanolithography, surface patterning and high resolution imaging is the focus of a considerable activity in the extreme ultraviolet (EUV) or soft x-ray (SXR) spectral regions. We report on the result of a study of the spectra from laser produced plasmas of a number of medium and high Z metals undertaken in order to identify potential sources for use with available multilayer mirrors. The main focus was the study of unresolved transition arrays emitted from ions with 3d, 4d and 4f valence subshells that emit strongly in the water window (2.34-4.38 nm).and that could be used for biological imaging or cell tomography.

Much effort has gone into the development of plasmas as sources of radiation in the 2 to 9 nm region in recent times with particular interests in the "water window" region (2.3 to 4.4 nm) and the 6.X nm region. Plasmas were formed on a range of targets of medium to high atomic number (Z) elements using Nd:YAG lasers with various illumination parameters. Spectra were recorded using a 0.25 m grazing-incidence spectrograph and spectral analysis was carried out with the aid of Hartree-Fock with configuration interaction calculations using the Cowan suite of codes [1].

Resonant triple-differential cross-section (TDCS) measurements have been used to study the double photoionization process in strontium. Two sets of measurements were made at the photon energy of the 4p ? 4d resonance. The coplanar geometry was used and the fixed analyser, positioned at ?90? to the main axis of polarization of the photons, detected electrons with ~65% of the available excess energy. The mutual angle between the two electrons had a range just short of 90 ? 270?. The TDCS exhibit unexpected lobes at a mutual angle of 180?. Comparison with other measurements made with the same geometry but with different sharings of the available energy indicate that these TDCS all show the unexpected lobe. Some possible explanations for the lobe are considered.

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.