Highly Charged Ions at GSI
For extensive tests of the quantum electrodynamic theory, laser spectroscopy of highly charged ions provides an excellent test ground. In the SPECTRAP facility, systematic measurements on severalspecies of highly charged ions will be possible with up to three orders of magnitude better spectroscopic resolution than in former experiments.
The setup will consist of the cryogenic Penning trap (SPECTRAP) which will be loaded by the HITRAP-facility with highly charged ions, a controllable laser and a detection system. The open-endcap cylindrical Penning trap developed in collaboration with the Imperial College London is performing tests at the Mainz University. The detectors will be provided by the University of Münster. The development of the laser system for the spectroscopy of Bi82+ is done at the Technical University of Darmstadt.
The required wavelength of 243,87(4) nm is provided by a 975 nm diode laser which is amplified and frequency-quadrupled in two cascaded second-harmonic generation stages. This enables a wide tuning range which can be achieved modehop free over approximately 80 GHz (UV) and by manually tuning of the grating stabilized master oscillator over approximately 5 nm (UV).
The master oscillator is stabilized to a resonator. This resonator is stabilized to a tunable laser system consisting of two diode lasers that can be detuned by a RF-Synthesizer with respect to a spectroscopic rubidium probe at 780 nm. This tunable offset lock allows precise control of the resonance frequency of the cavity.