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Abstract

We report about high-precision wavelength determination of H-like and He-like ions at the Heidelberg Electron Beam Ion Trap (HD-EBIT). The experiment was carried out with a novel flat crystal (Si-111) spectrometer applying a reference technique without collimation. The result for the transition energy of the 1s2p 1P1→ 1s2 1S0 resonance line in He-like S14+ agrees with theoretical predictions with an experimental accuracy five times higher than earlier experiments. The same line in Ar16+ was measured with a relative uncertainty of δλ/λ = 2 × 10-6, a factor of 2.5 more accurate than any X-ray wavelength in highly charged ions ever reported, and for He-like ions probes QED two-electron and two-photon radiative corrections. Beside relative wavelength measurements absolute ones were carried out using the Bond method. The results point at the possibility of establishing absolute Lyman-α1 transition X-ray wavelength standards in the future.