Generation of neutral atomic beams utilizing photodetachment by high power diode laser stacks.

We demonstrate the use of high power diode laser stacks to photodetach fast hydrogen and carbon anions and produce ground term neutral atomic beams. We achieve photodetachment efficiencies of ∼7.4% for H(-) at a beam energy of 10 keV and ∼3.7% for C(-) at 28 keV. The diode laser systems used here operate at 975 nm and 808 nm, respectively, and provide high continuous power levels of up to 2 kW, without the need of additional enhancements like optical cavities. The alignment of the beams is straightforward and operation at constant power levels is very stable, while maintenance is minimal. We present a dedicated photodetachment setup that is suitable to efficiently neutralize the majority of stable negative ions in the periodic table.

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

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.

Experimental results for H2 formation from H- and H and implications for first star formation.

During the epoch of first star formation, molecular hydrogen (H2) generated via associative detachment (AD) of H- and H is believed to have been the main coolant of primordial gas for temperatures below 10(4) kelvin. The uncertainty in the cross section for this reaction has limited our understanding of protogalaxy formation during this epoch and of the characteristic masses and cooling times for the first stars. We report precise energy-resolved measurements of the AD reaction, made with the use of a specially constructed merged-beams apparatus. Our results agreed well with the most recent theoretically calculated cross section, which we then used in cosmological simulations to demonstrate how the reduced AD uncertainty improves constraints of the predicted masses for Population III stars.

A simple double-focusing electrostatic ion beam deflector.

We have developed an electrostatic, double-focusing 90 degrees deflector for fast ion beams consisting of concentric cylindrical plates of differing heights. In contrast to standard cylindrical deflectors, our design allows for focusing of an incoming parallel beam not only in the plane of deflection but also in the orthogonal direction. The optical properties of our design resemble those of a spherical capacitor deflector while it is much easier and more cost effective to manufacture.

A novel merged beams apparatus to study anion-neutral reactions.

We have developed a novel laboratory instrument for studying gas phase, anion-neutral chemistry. To the best of our knowledge, this is the first such apparatus which uses fast merged beams to investigate anion-neutral chemical reactions. As proof-of-principle we have detected the associative detachment reaction H(-)+H-->H(2)+e(-). Here we describe the apparatus in detail and discuss related technical and experimental issues.

Testing QED screening and two-loop contributions with He-Like ions.

We report wavelength measurements of H-like and He-like ions obtained with a novel x-ray spectrometer at the Heidelberg Electron Beam Ion Trap. The experimental uncertainty for the Lyman-alpha1 wavelength in Cl16+ is reduced by a factor of 3 and, as expected, excellent agreement with theory is maintained. For the resonance line in He-like Ar16+, an uncertainty of only deltalambda/lambda=2x10(-6) was achieved. This is the most precise x-ray wavelength reported for highly charged ions to date, and allows to test recent predictions on QED two-electron and two-photon radiative corrections for He-like ions. The results also point to the advantages of establishing absolute x-ray wavelength standards using Lyman-alpha transitions (in the present case Ar17+ Lyman-alpha1) to supersede the current ones.

Exploring relativistic many-body recoil effects in highly charged ions.

The relativistic recoil effect has been the object of experimental investigations using highly charged ions at the Heidelberg electron beam ion trap. Its scaling with the nuclear charge Z boosts its contribution to a measurable level in the magnetic-dipole (M1) transitions of B- and Be-like Ar ions. The isotope shifts of 36Ar versus 40Ar have been detected with sub-ppm accuracy, and the recoil effect contribution was extracted from the 1s(2)2s(2)2p 2P(1/2) - 2P(3/2) transition in Ar13+ and the 1s(2)2s2p 3P1-3P2 transition in Ar14+. The experimental isotope shifts of 0.00123(6) nm (Ar13+) and 0.00120(10) nm (Ar14+) are in agreement with our present predictions of 0.00123(5) nm (Ar13+) and 0.00122(5) nm (Ar14+) based on the total relativistic recoil operator, confirming that a thorough understanding of correlated relativistic electron dynamics is necessary even in a region of intermediate nuclear charges.

Relativistic electron correlation, quantum electrodynamics, and the lifetime of the 1s(2)2s(2)2p2p0(3/2) level in boronlike argon.

The lifetime of the Ar13+ 1s(2)2s(2)2p2p0(3/2) metastable level was determined at the Heidelberg Electron Beam Ion Trap to be 9.573(4)(5). The accuracy level of one per thousand makes this measurement sensitive to quantum electrodynamic effects like the electron anomalous magnetic moment (EAMM) and to relativistic electron-electron correlation effects like the frequency-dependent Breit interaction. Theoretical predictions, adjusted for the EAMM, cluster about a lifetime that is approximately shorter than our experimental result.

State-selective quantum interference observed in the recombination of highly charged Hg 75+...78+ mercury ions in an electron beam ion trap.

We present experimental data on the state-selective quantum interference between different pathways of photorecombination, namely, radiative and dielectronic recombination, in the KLL resonances of highly charged mercury ions. The interference, observed for well resolved electronic states in the Heidelberg electron beam ion trap, manifests itself in the asymmetry of line shapes, characterized by "Fano factors," which have been determined with unprecedented precision, as well as their excitation energies, for several strong dielectronic resonances.