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.