Resonant-line overlap for photopumping and spoiling of x-ray lasing transitions in neonlike Fe xvii and Cu xx

High-precision measurements (25--175 ppm) have been performed of selected 2p-3s and 2p-4d transitions in neonlike Fe and Cu that are of possible use in resonant photopumping x-ray lasing experiments. A marginal resonance of 600 ppm is found for the 2p-4d transition in neonlike Fe with the 1s-2p transition in hydrogenic Ne. By contrast, an excellent resonance of 200 ppm is determined for photopumping of the 2p-4d transition in neonlike Cu with the 1s-2p transition in heliumlike Mg, suggesting that the Cu-Mg pair is a good candidate for resonant photopumping experiments. Moreover, the separation of the 2p-3s transition in neonlike Fe and the 1s-2p transition in heliumlike F is measured to assess the resonance for use in a scheme to spoil x-ray lasing. The overlap (2000 ppm), however, appears insufficient.