Beam Energy Determination Via Collinear Laser Spectroscopy

An approach to determine the kinetic beam energy at the 10(-5) level is presented, which corresponds to an improvement by more than one order of magnitude compared with conventional methods. Particularly, collinear fluorescence and resonance-ionization spectroscopy measurements on rare-isotope beams, where the beam energy is a major contribution to the uncertainty, can benefit from this method. The approach is based on collinear spectroscopy and requires no special equipment besides a wavelength meter, which is commonly available. Its advent is demonstrated in a proof-of-principle experiment on a Ni beam. In preparation for the energy measurement, the rest-frame transition frequencies of the 3d(9)4s(3)D(3) -> 3d(9)4p(3)P(2) transitions in neutral nickel isotopes have been identified to be nu(0)(Ni-58) = 850 343 678 (20) MHz and nu(0)(Ni-60) = 850 344 183 (20) MHz.