Absolute line intensities for photon pumping of x-ray lasers

Absolute intensities of certain resonance lines which are considered to be promising candidates for matched-line (photoexcitation) pumping of x-ray lasers are measured. Most are in the 3--8-nm wavelength range. A promising Na⁹⁺ candidate at 1.1 nm is also tested. The measured radiation is emitted from high-density plasmas formed near the surface of laser-heated slab targets of selected materials. It is concluded that gain-length products of 3 can be achieved with a driving-laser irradiance of 10¹² W/cm² and with characteristic dimensions in the 10--100-{μ}m range. Also, among the one-, two-, and three-electron ions tested, an apparent decreasing 2p{→}1s, 3d{→}2p, 3p{→}2s order of preference for resonance pumping transitions may exist, subject to limitations of the present measurement accuracy. One 3d{→}2p transition in a neonlike ion is proven to be a particularly poor pumping candidate; however, the 3s{→}2p transition appears to be more promising.