Collinear laser spectroscopy of highly charged ions produced with an electron beam ion source

Collinear laser spectroscopy has been performed on He-like C$^{4+}$ ions extracted from an electron beam ion source (EBIS). In order to determine the transition frequency with the highest-possible accuracy, the lineshape of the fluorescence response function was studied for pulsed and continuous ion extraction modes of the EBIS in order to optimize its symmetry and linewidth. We found that the best signal-to-noise ratio is obtained using the continuous beam mode for ion extraction. Applying frequency-comb-referenced collinear and anticollinear laser spectroscopy, we achieved a measurement accuracy of better than 2\,MHz including statistical and systematic uncertainties. The origin and size of systematic uncertainties, as well as further applications for other isotopes and elements are discussed

Collinear Laser Spectroscopy of 2 3 ⁣S1→2 3 ⁣P ⁣J2\,{}^3\!S_1 \rightarrow 2\,{}^3\!P_{\!J} transitions in helium-like 12C4+^{12}\mathrm{C}^{4+}

Transition frequencies and fine-structure splittings of the $2\,{}^3\!S_1 \rightarrow 2\,{}^3\!P_{\!J}$ transitions in helium-like $^{12}\mathrm{C}^{4+}$ were measured by collinear laser spectroscopy on a 1-ppb level. Accuracy is increased by more than three orders of magnitude with respect to previous measurements, enabling tests of recent non-relativistic QED calculations including terms up to $m\alpha^7$. Deviations between the theoretical and experimental values are within theoretical uncertainties and are ascribed to $m\alpha^8$ and higher-order contributions in the series expansion of the NR-QED calculations. Finally, prospects for an all-optical charge radius determination of light isotopes are evaluated

On the performance of wavelength meters: Part 2 — frequency-comb based characterization for more accurate absolute wavelength determinations

Wavelength meters are widely used for frequency determinations and stabilization purposes since they cover a large wavelength range, provide a high read-out rate and have specified accuracies of up to 10⁻⁸. More accurate optical frequency measurements can be achieved with frequency combs but only at the price of considerably higher costs and complexity. In the context of precise and accurate frequency determinations for high-resolution laser spectroscopy, the performance of five different wavelength meters was quantified with respect to a frequency comb. The relative precision as well as the absolute accuracy has been investigated in detail, allowing us to give a sophisticated uncertainty margin for the individual instruments. We encountered a prominent substructure on the deviation between both device types with an amplitude of a few MHz that is repeating on the GHz scale. This finally limits the precision of laser scans which are monitored and controlled with wavelength meters. While quantifying its uncertainty margins, we found a high temporal stability in the characteristics of the wavelength meters which enables the preparation of wavelength-dependent adjustment curves for wide- and short-ranged scans. With this method, the absolute accuracy of wavelength meters can be raised up to the MHz level independently from the wavelength of the reference laser used for calibrating the device. Since this technique can be universally applied, it can lead to benefits in all fields of wavelength meter applications

The large GTPase Sey1/atlastin mediates lipid droplet- and FadL-dependent intracellular fatty acid metabolism of Legionella pneumophila

The amoeba-resistant bacterium Legionella pneumophila causes Legionnaires' disease and employs a type IV secretion system (T4SS) to replicate in the unique, ER-associated Legionella-containing vacuole (LCV). The large fusion GTPase Sey1/atlastin is implicated in ER dynamics, ER-derived lipid droplet (LD) formation, and LCV maturation. Here, we employ cryo-electron tomography, confocal microscopy, proteomics, and isotopologue profiling to analyze LCV-LD interactions in the genetically tractable amoeba Dictyostelium discoideum. Dually fluorescence-labeled D. discoideum producing LCV and LD markers revealed that Sey1 as well as the L. pneumophila T4SS and the Ran GTPase activator LegG1 promote LCV-LD interactions. In vitro reconstitution using purified LCVs and LDs from parental or Δsey1 mutant D. discoideum indicated that Sey1 and GTP promote this process. Sey1 and the L. pneumophila fatty acid transporter FadL were implicated in palmitate catabolism and palmitate-dependent intracellular growth. Taken together, our results reveal that Sey1 and LegG1 mediate LD- and FadL-dependent fatty acid metabolism of intracellular L. pneumophila

Collinear Laser Spectroscopy of Helium-like ¹¹B³⁺

Collinear laser spectroscopy in the 1s2s³S₁→1s2p³P₀,₂ transitions of helium-like ¹¹B³⁺ was performed using the HITRAP beamline at the GSI Helmholtz Centre. The ions were produced in an electron beam ion source, extracted, and accelerated to a beam energy of 4 keV/q. Results agree with previous measurements within uncertainty. Thus, it was demonstrated that the metastable state in He-like ions is sufficiently populated to carry out collinear laser spectroscopy. The measurement is a pilot experiment for a series of measurements that will be performed at a dedicated collinear laser spectroscopy setup at TU Darmstadt with light helium-like ions

Laser Spectroscopy of the Boron Isotopic Chain

The charge radius of a nucleus is a fundamental physical property that corresponds to the binding strength and the structure of the bound nuclear system. This observable is particularly important for the investigation of so-called halo nuclei, which consist of a compact nuclear core with typical nuclear density and a dilute cloud of halo nucleons. Neutron halo nuclei have been subject to numerous investigations, but little is known about proton-halo systems. The isotope 8B is believed to be a prototype of a proton-halo, which was concluded indirectly from measurements of its quadrupole moment and analysis of the momentum distribution of breakup fragments. High-precision laser spectroscopy can provide direct proof of the halo structure by measuring the nuclear charge radius. Such measurements were performed previously for the most prominent (neutron) halo isotopes up to Z = 4 (beryllium). Extending these investigations to the boron isotopes (Z = 5) is the subject of this thesis. It covers the design and installation of the experimental setup for the on-line measurement of the short-lived 8B (t1/2 = 770 ms) as well as first off-line measurements of the charge radius difference between the two stable isotopes 10B and 11B. The halo-candidate 8B is produced in a 3He(6 Li,8B)n reaction in inverse kinematics and the energetic 8B ions are stopped in a gas cell and then transported to the collinear beamline by radiofrequency ion guides. The production of 8B was optimized by improving the cryogenic gas target to avoid saturation effects. It was observed that the 8B ions that leave the gas cell have water molecules attached. While this improves the transport process, it prohibits laser spectroscopy on the atomic system. Therefore, a molecular breakup station based on the transmission of the molecules through nanometer-thin carbon foils was designed, built and tested. The apparatus to perform collinear laser spectroscopy was also installed at the experimental site during this work and the performance of its fluorescence detection region has been significantly improved. The progress achieved represents a significant step towards laser spectroscopy on the exotic proton-halo candidate 8B in the near future. The isotope shift between the stable isotopes of boron 10B and 11B was measured on a collimated atomic beam. Beams of two lasers crossed the atomic beam in perpendicular alignment to perform resonance ionization mass spectrometry. The first laser excited the 2p → 3s ground state transition and the second laser was used for non-resonant ionization of the excited atoms. Exact control of the overlap angle of laser and the atomic beam is essential to eliminate the first-order Doppler effect, which otherwise introduces significant uncertainties for the spectroscopy of these light ions. Therefore, an elaborated double-pass scheme has been used where the uncertainty in the overlap angle was minimized together with other sources of systematic uncertainties that are typically prevalent in laser spectroscopy. The isotope shift between 10B and 11B was measured for the first time with sufficient accuracy to extract the difference in the mean-square nuclear charge radius. Results are compared with predictions from state-of-the-art ab-initio nuclear structure theories and show reasonable agreement with the no-core shell model as well as Green’s function Monte Carlo calculations

Transition frequencies and hyperfine structure in 113,115In+^{113 , 115}In^+ : Application of a liquid-metal ion source for collinear laser spectroscopy

We demonstrate the first application of a liquid-metal ion source for collinear laser spectroscopy in proof-of-principle measurements on naturally abundant In$^+$. The superior beam quality, i.e., the actively stabilized current and energy of a beam with very low transverse emittance, allowed us to perform precision spectroscopy on the 5s^2\;^1\mathrm{S}_0 \rightarrow 5s5p\;^3\mathrm{P}_1 intercombination transition in $^{115}$In$^+$, which is to our knowledge the slowest transition measured with collinear fluorescence laser spectroscopy so far. By applying collinear and anticollinear spectroscopy, we improved the center-of-gravity frequency $\nu_\mathrm{cg}=1\,299\,617\,759.\,3\,(1.2)$ and the hyperfine constants $A=6957.19\,(28)$\,MHz and $B=-443.7\,(2.4)$\,MHz by more than two orders of magnitude. A similar accuracy was reached for $^{113}$In$^+$ in combination with literature data and the isotope shift between both naturally abundant isotopes was deduced to $\nu(^{113}\mathrm{In})-\nu(^{115}\mathrm{In})=696.3\,(3.1)$\,MHz. Nuclear alignment induced by optical pumping in a preparation section of the ion beamline was demonstrated as a pump-and-probe approach to provide sharp features on top of the Doppler broadened resonance profile

On the performance of wavelength meters: Part 2 — frequency-comb based characterization for more accurate absolute wavelength determinations

Wavelength meters are widely used for frequency determinations and stabilization purposes since they cover a large wavelength range, provide a high read-out rate and have specified accuracies of up to 10⁻⁸. More accurate optical frequency measurements can be achieved with frequency combs but only at the price of considerably higher costs and complexity. In the context of precise and accurate frequency determinations for high-resolution laser spectroscopy, the performance of five different wavelength meters was quantified with respect to a frequency comb. The relative precision as well as the absolute accuracy has been investigated in detail, allowing us to give a sophisticated uncertainty margin for the individual instruments. We encountered a prominent substructure on the deviation between both device types with an amplitude of a few MHz that is repeating on the GHz scale. This finally limits the precision of laser scans which are monitored and controlled with wavelength meters. While quantifying its uncertainty margins, we found a high temporal stability in the characteristics of the wavelength meters which enables the preparation of wavelength-dependent adjustment curves for wide- and short-ranged scans. With this method, the absolute accuracy of wavelength meters can be raised up to the MHz level independently from the wavelength of the reference laser used for calibrating the device. Since this technique can be universally applied, it can lead to benefits in all fields of wavelength meter applications