X-ray laser experiments using laser-vaporized copper-foil plasmas

Recent exploratory experiments used laser-vaporized copper films in a search for gain on 3s–3p transitions in neonlike Cu xx plasmas. The Naval Research Laboratory Pharos iii laser was operated at 100–330 J with mostly 2-nsec pulses. The plasma length, the laser energy and pulse shape, and the copper thickness were varied. Vacuum-ultraviolet and x-ray spectroscopy and pinhole photography measured axial emission, homogeneity, front–rear symmetry, and electron temperature. A novel slotted-copper-foil target showed similar characteristics. Spectral features from a selenium target are described. A distinct dependence of plasma expansion and radiative transport on the rise-time characteristics of the laser pulse is observed. Various explanations for the lack of distinguishable gain in these initial tests are discussed.