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 ${\mathrm{Na}}^{9+}$ 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 ${10}^{12}$ W/${\mathrm{cm}}^2$ and with characteristic dimensions in the 10–100-μm 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.