PRECISION LIFETIME MEASUREMENTS ON ALKALI ATOMS AND ON HELIUM BY BEAM-GAS-LASER SPECTROSCOPY

The results of a new series of precision lifetime measurements on alka li atoms by means of beam-gas-laser spectroscopy are reported and disc ussed. The lifetimes of the Ist excited states in lithium, sodium, pot assium and rubidium were measured with uncertainties ranging from +/-0 .14% to +/-0.25%. The results are discussed in comparison with other r ecent experimental and theoretical work. The longstanding discrepancy between ab initio line strength calculations and the measurements of G aupp et al. [Phys. Rev. A26, 3351 (1982)] for the resonance transition s in lithium and sodium is resolved by the new measurements in favour of the theoretical calculations. Finally the role bf the beam divergen ce in lifetime measurements on fast particle beams is discussed and a method to correct far this effect is presented. The importance of the beam divergence effect is illustrated by additional recent lifetime me asurements on helium and on lithium.