Absolute line intensities for photon pumping of x-ray lasers

Abstract

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-\ensuremath{\mu}m range. Also, among the one-, two-, and three-electron ions tested, an apparent decreasing 2p\ensuremath{\rightarrow}1s, 3d\ensuremath{\rightarrow}2p, 3p\ensuremath{\rightarrow}2s order of preference for resonance pumping transitions may exist, subject to limitations of the present measurement accuracy. One 3d\ensuremath{\rightarrow}2p transition in a neonlike ion is proven to be a particularly poor pumping candidate; however, the 3s\ensuremath{\rightarrow}2p transition appears to be more promising.