High-precision laser-assisted absolute determination of x-ray diffraction angles

Abstract

A novel technique for absolute wavelength determination in high-precision crystal x-ray spectroscopy recently introduced has been upgraded reaching unprecedented accuracies. The method combines visible laser beams with the Bond method, where Bragg angles (θ and -θ) are determined without any x-ray reference lines. Using flat crystals this technique makes absolute x-ray wavelength measurements feasible even at low x-ray fluxes. The upgraded spectrometer has been used in combination with first experiments on the 1s2p(1)P(1) → 1s(2)(1)S(0) w-line in He-like argon. By resolving a minute curvature of the x-ray lines the accuracy reaches there the best ever reported value of 1.5 ppm. The result is sensitive to predicted second-order QED contributions at the level of two-electron screening and two-photon radiative diagrams and will allow for the first time to benchmark predicted binding energies for He-like ions at this level of precision.

Chantleret al.Reply:

“…A similar analysis for the expanded data set gives n ¼ 5:0, but with 2 r being high: 2.4. Although the inclusion of the new datum [4] does not change the main conclusions of our earlier paper [3], and the exponent is in reasonable agreement with our previous result, the minimum 2 r more than doubles, suggesting that the expanded data set includes a data point with greatly underestimated uncertainty or that the assumed form of the deviation should be revised.…”

Experimental study of the x-ray transitions in the heliumlike isoelectronic sequence: Updated results

“…4. The scaling by Chantler et al treats the two highly precise measurements of A rl(l+ [27,28] as outliers [34]. Our datum will undoubtedly be treated similarly, but no more so than they treat their own datum for V2I+ [21], the A rl6+ datum from Deslaltes et al [9], and the three points from Engstrom and Litzen [31] as outliers.…”

“…This is true also today, as several very high precision measurements of Arl6+ have been recently reported with uncertainties as low as 2 ppm [27][28][29], although very recently some of these uncertainties have been revised upward by a factor of two [30]. These measurements again were performed using an electron beam ion trap.…”

Transition energies of theDlines in Na-like ions

“…In Table IV, we compare our result to some of the most accurate tests available in other few-electron highly charged ions [17,[31][32][33][34][35][36]. The results for H-like ions were reported by Gumberidze et al [33] in terms of binding energies, but we have used the information contained in their paper to extract the transition energies shown here (this also removes their assumption that there is zero error in the upper calculated level).…”

“…For high Z, R QED is currently limited by experiment for the hydrogen sequence, by theory for the lithium sequence, and shared roughly equally by theory and experiment for the sodium sequence. For the helium sequence, a recent analysis [37] suggests that the uncertainty in theory and/or experiment may have been underestimated, but in Table IV we quote the results for He-like Ar as originally published [32,34].…”