PhD topic: Laser spectroscopy of Be-like krypton ions at the ESR

Heavy few-electron ions, such as He-, Li-, and Be-like ions, are ideal atomic systems to study effects of correlation, relativity and quantum electrodynamics. Very recently, theoretical and experimental studies of these species achieved a considerable improvement in accuracy. The Be-like ions are interesting because their first excited state, i.e. the (1s22s2p) 3P0, has an almost infinite lifetime in the absence of nuclear spin (I), as it can only decay by a two-photon E1M1 transition to the (1s22s2) 1S0 ground state. If the nucleus has spin, the corresponding hyperfine structure will reduce this lifetime by orders of magnitude. In addition, the energy difference between the 3P0 and the 3P1 states is expected to be almost completely unaffected by radiative QED effects, and is therefore dominated by the effects of correlation and relativity. We want to determine the (1s22s2p) 3P0 - 3P1 level splitting in Be-like krypton (84Kr32+), which has I=0, by means of laser spectroscopy at the Experimental Storage Ring (ESR) at GSI in Darmstadt. In such an experiment, the energy splitting can be obtained with very good accuracy, i.e. of the order of ~10-5, and be compared with recent calculations.

In April 2010 we successfully applied for a beamtime to perform the proposed experiment at the ESR, and were granted all requested 18 shifts (1 shift = 8 hours). In principle, this means that the experiment can be performed whenever we are ready. The PhD student should be concerned with setting up the detection system and the laser system, in order to perform the laser spectroscopy measurements at the ESR. The detection system should be based on MCP technology, and must be designed, constructed, and tested for the detection of photons with an energy of about 120 eV. The laser system has to be set up, tested, and be routinely operational for the beamtime.

We are looking for a motivated candidate with a degree (bachelor, master, Diplom) in physics. It would be very advantageous when the candidate already has some experience with lasers, or ions, or detectors. During the PhD period, you will learn about: particle confinement, manipulation and detection at the ESR, ion sources and ion optics, vacuum techniques, and high-precision laser spectroscopy (i.e. laser excitation and light detection). Also, you will have the opportunity to work in one of the world's best laboratories for experiments with exotic ions (heavy highly-charged ions). You will be part of a multi-cultural team of excellent scientists, which collaborates with other well-known research groups from all over the world.


Location: GSI Darmstadt

Start: as soon as possible

Duration: 3 years

Salary: PhD stipend

PhD students at GSI are a member of HGS-HIRe for FAIR


This project also offers good possibilities for master or Diploma theses!



Dr. Danyal Winters (project supervisor)

Phone: +49 (0)6159 71 2125

E-Mail: d.winters(at)


Prof. Dr. Thomas Stöhlker (PhD supervisor)

Phone: +49 (0)6159 71 2722

E-Mail: t.stoehlker(at)