A new Collinear Apparatus for Laser Spectroscopy and Applied Science (COALA)

High voltage determination and stabilization for collinear laser spectroscopy applications

Fast beam collinear laser spectroscopy is the established method to investigate nuclear ground state properties such as the spin, the electromagnetic moments, and the charge radius of exotic nuclei. These are extracted with high precision from atomic observables, i.e., the hyperfine splitting and the isotope shift, which become possible due to a large reduction of the Doppler broadening by compressing the velocity width of the ion beam through electrostatic acceleration. With the advancement of experimental methods and applied devices, e.g., to measure and stabilize the laser frequency, the acceleration potential became the dominant systematic uncertainty contribution. To overcome this, we present a custom-built high-voltage divider, which was developed and tested at the German metrology institute, and a feedback loop that enabled collinear laser spectroscopy to be performed at a 100-kHz level. Furthermore, we describe the impact of field penetration into the laser-ion interaction region. This affects the determined isotope shifts and hyperfine splittings if Doppler tuning is applied, i.e., the ion beam energy is altered instead of scanning the laser frequency. Using different laser frequencies that were referenced to a frequency comb, the field penetration was extracted laser spectroscopically. This allowed us to define an effective scanning potential to still apply the faster and easier Doppler tuning without introducing systematic deviations.

Collinear Laser Spectroscopy of 2 ^{3}S_{1}→2 ^{3}P_{J} Transitions in Helium-like ^{12}C^{4+}

Transition frequencies and fine-structure splittings of the 2 ^{3}S_{1}→2 ^{3}P_{J} transitions in helium-like ^{12}C^{4+} were measured by collinear laser spectroscopy on a 1-ppb level. Accuracy is increased by more than 3 orders of magnitude with respect to previous measurements, enabling tests of recent nonrelativistic (NR) QED calculations including terms up to mα^{7}. Deviations between the theoretical and experimental values are within theoretical uncertainties and are ascribed to mα^{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.

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.