Transitions in lithiumlike Cu^26+ and berylliumlike Cu^25+ of interest for x-ray laser research

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Abstract
Transitions in highly charged copper ions have been identified in the extreme-ultraviolet spectra from plasmas produced by the Omega laser at the University of Rochester. The 24 beams of the Omega laser were focused to separate spots of diameter 50 μm upon the surface of copper-coated targets 600 μm in diameter. The transitions in lithiumlike Cu26+ and berylliumlike Cu25+ of the type n = 3–4 were observed in the wavelength region 24 to 28 Å and were bright in the focal regions. The intensities of the Cu26+ 2p–3d and 3d–4f transitions indicate that a population inversion occurs between the 3d and 4f levels. Comparisons of the observed relative intensities of the Cu26+ transitions with calculated intensities indicate that the Cu26+ spectrum originates in a plasma region with an electron density of order of 1020 cm−3 and that collisional recombination is important for populating the 4f level. The 3d–4f transitions at 25.525and 25.636 Å in Cu26+, and the same transitions in neighboring elements, appear to be good candidates for achieving gain at wavelengths below the carbon absorption edge at 43.5 Å.