old_02_double_res
Laser-rf double-resonance spectroscopy in a storage ring
M. Kristensen, J. S. Hangst, P. S. Jessen, J. S. Nielsen, O. Poulsen, and P. Shi
Institute of Physics and Astronomy, University of Aarhus, DK-8000 Århus, C Denmark
Laser-rf double-resonance spectroscopy of the hyperfine transition between F”=0 and F’= 1 in the metastable ‘Sl state of Li+ was performed in 100-keV beam in the storage ring ASTRID. High efficiency of optical pumping was demonstrated for complex pumping schemes. A broadband (dc —6 GHz) rf device was designed and used for rf spectroscopy in the storage ring. The possibility of obtaining coherent rf signals (Ramsey fringes) from successive interactions with the same field was investigated. Important limitations for the coherences due to magnetic-field inhomogeneities were observed. These led to randomization of the atomic polarization during only one turn in the storage ring and completely prevented observation of Ramsey fringes. This situation is different from the case of fundamental particles in a storage ring, where the polarization may be preserved for many round-trips. Limits were put on the demands to beam quality, beam positioning, and magnetic-field quality to overcome the problem. The effects of the rf device on the external degrees of freedom of the ion beam were investigated. Its small aperture substantially reduced the beam lifetime, and at very low rf frequencies the electric field in the rf device was able to excite external transverse resonances in the beam.