LASER SCANNING MEASUREMENT OF THE DENSITY DISTRIBUTION OF CONFINED LI-6(+) IONS

The density distribution of metastable 1s2s 3S1 Li+ ions confined in a radio-frequency quadrupole ion trap has been studied using a laser scanning technique. The laser beam, resonant with the 5485-Å 1s2s 3S1-1s2p 3P1 transition, is scanned in a plane normal to the trap z axis. Intercombination photons, 1s2 1S0-1s 2p 3P 1 at 202 Å, are counted and stored as a function of laser-beam position. Application of the Abel transform to the data gives the density profile in the plane of the scan. In all cases, the density profiles were consistent with a Gaussian distribution of ions. The radial and axial widths of the distribution were measured as a function of the number of ions and potential well depth and shape. The results are discussed in terms of a model in which the ions are in thermal equilibrium at a temperature of several thousand degrees Kelvin.