P. Seelig

Laser spectroscopy of the 1s HFS of H-like ions at a bunched beam in the storage ring ESR

The investigation of the 1s HFS provides a good possibility for testing QED effects in a combination of a strong electric and magnetic field. Here, we report about the laserspectroscopic measurements of the ground state hyperfine splitting in 207Pb81+. To handle this M1-transition in the infrared optical regime with its long lifetime, we developed a new detection technique using a bunched ion beam. For the observation of fluorescence light, a new mirror system is adapted to the emission characteristics from an ion beam at relativistic velocities.

New access to the magnetic moment distribution in the nucleus by laser spectroscopy of highly charged ions

Abstract The availability of high intensity, high quality beams of highly charged ions has started a new application for laser spectroscopy. High resolution spectroscopy can now be applied to a study of hydrogen-like atomic states in heavy elements. In principal, this will allow a determination of the hyperfine splitting with an accuracy in the 10 −6 -range or better. Presently this exceeds the limits given by the uncertainties of the nuclear quantities, especially the distribution of the nuclear magnetization in the nucleus. Since the new approach can be applied to a family of test cases, it can provide a wide experimental basis for the separation of nuclear and QED effects. This is especially true since measurements of the hyperfine splitting have now also been performed at the Super-EBIT ion trap. For the determination of nuclear parameters it will be of benefit to measure more candidates close to the doubly magic 208 Pb. In such systems theoretical efforts to clarify details of the nuclear structure and of the interaction between the nucleus and the electron can be expected to even surpass the present experimental accuracy.

Laser systems specialized for laser spectroscopy at storage rings

Laser spectroscopy at storage rings often suffers from a limited resolution due to Doppler-broadened resonances. Broadening is caused by the velocity spread of the ions stored in the beam. In the following, the present status of our work on laser systems specialized on the specific needs of laser spectroscopy at storage rings is reported.Two pulsed laser systems were developed. One is a dye laser whose spectral bandwidth can be switched by inserting different Littrow-prisms into the resonator. An increase in bandwidth up to a factor of 45 was achieved. This laser was used for fast qualitative scans and high resolution measurements. The other laser system is a Nd : YAG laser pumped optical parametric oscillator. It is a tunable laser system covering the spectral range from 410 to 4000 nm. Furthermore, a continuous wave laser with a frequency shifted feedback cavity is described. It shows broadband emission with an adjustable bandwidth of up to 4.5 GHz. This laser can be advantageous for laser cooling of ion beams.

Population and spectroscopy of highly‐charged ions by laser‐induced recombination in the ESR

Laser‐induced two‐step recombination of bare Ar18+ ions with free electrons was obtained at the ESR storage ring of GSI, with spectral resolution a factor of 15 better than earlier measurements. The pulses of a Nd:YAG laser, overlapped with the ion beam and the cooling electron beam, induced transitions from the continuum to high‐lying Rydberg states. To avoid field ionization in the bending magnet before reaching the detector, a transfer to a final state well below the reionization threshold was required. Executing this second step with a narrow‐band dye laser yielded a line width almost at the Doppler limit. Consequently, a spectroscopic determination of the velocity β of the ion beam was achieved.

Bunched laser cooling of a stored weak 7Li+ ion beam in a pure triplet state

A preparation scheme for a 7Li+ ion beam in a storage ring is presented which provides ions in the metastable triplet states with well controlled longitudinal phase space properties. For both state selective preparation and beam cooling, laser- and electron-cooler forces are applied. The spatial- and momentum distributions of the ions are directly detected by a time resolved measurement of the fluorescence light. At low beam intensities, the remaining heating rate of such a beam is completely determined by residual gas scattering.

Ion beam preparation of 7Li+ for precision experiments at heavy ion storage rings

Abstract Heavy ion storage rings allow for tests of the structure of local space time via the Doppler effect. At the TSR/Heidelberg an experiment with high resolution laser spectroscopy at 7 Li + is performed. To gain the maximum resolution for saturation spectroscopy new methods of relativistic ion beam preparation and diagnostics have been developed. The laser cooling of the beam allows for precision determination of the mean velocity of the ions. A novel phase synchronous detection scheme, ultimately sensitive to single ions, gives insights into the cooling mechanism and dynamics. With an additional synchronous excitation scheme systematic uncertainties of the test experiment can be drastically reduced. After separation of the ground state ions from the triplet states of 7 Li + by the combination of laser and electron cooling, a bunched and cooled ensemble of fast moving high precision clocks with minimized perturbations by space charge effects and intra beam scattering is available.

Preparation of relativistic 7Li+ ion beams for precision experiments at storage rings

Heavy ion storage rings allow for tests of the structure of local space time via the Doppler effect. At the TSR/Heidelberg an experiment with high resolution laser spectroscopy at 7Li+ is performed. To gain the maximum resolution for saturation spectroscopy new methods of relativistic ion beam preparation and diagnostics have been developed.The laser cooling of the beam allows for precision determination of the mean velocity of the ions. A novel phase synchronous detection scheme, ultimately sensitive to single ions, gives insights into the cooling mechanism and dynamics. With an additional synchronous excitation scheme systematic uncertainties of the test experiment can be drastically reduced. After separation of the ground state ions from the triplet states of 7Li+ by the combination of laser and electron cooling, a bunched and cooled ensemble of fast moving high precision clocks with minimized perturbations by space charge effects and intra beam scattering is available.

A NEW DETECTOR FOR LASER INDUCED RECOMBINATION AT THE ESR

For laser induced recombination of heavy ions a new detector was developed that in comparison to a multiwire proportional counter provides better time resolution. It is able to cope with very high rates and gives the possibility for very easy online monitoring of the detected beam.

Precision laser spectroscopy of highly charged ions

Recently, intense beams of highly charged ions have become available at heavy ion cooler rings. The obstacle for producing these highly interesting candidates is the large binding energy of K-shell electrons in heavy systems in excess of 100 keV. One way to remove these electrons is to strip them off by passing the ion through material. In the cooler ring, the ions are cooled to a well defined velocity. At the SIS/ESR complex it is possible to produce, store, and cool highly charged ions up to bare uranium with intensities exceeding 108 atoms in the ring. This opens the door for precision laser spectroscopy of hydrogenlike-heavy ions, e.g.209Bi82+, and allows to examine the interaction of the single electron with the large fields of the heavy nucleus, exceeding any artificially produced electric and magnetic fields by orders of magnitude. In the electron cooler the interaction of electrons and highly charged ions otherwise only present in the hottest plasmas can be studied.

New Tests of Special Relativity and QED by Laser Spectroscopy in Heavy Ion Storage Rings

The advent of heavy‐ion cooler rings has created a completely new scope for the application of laser spectroscopy on accelerator beams. The unique potential opened for laser spectroscopic applications by the exotic properties of the stored ions can be exploited to address fundamental problems of physics.The high, but very well controlled velocity of the ions has been used as a test ground for the theory of special relativity. The availability of highly‐charged ions beyond all previous possibilities has been exploited for precision laser spectroscopy of the ground state hyperfine splitting of heavy hydrogen‐like ions. This represents a novel opportunity to study QED corrections in the previously unexplored combination of strong magnetic and electric fields.