A note on the population densities of He excited states of n⩾3 and their contribution to the total Penning excitation rate in the positive column He-Cd+laser discharge

Population densities of He excited states of n>or=3 in a positive column He-Cd + laser were measured accurately using end light from a discharge tube. It is shown that the sum of these populations is certainly smaller by about one order of magnitude than the population density of the 2 3 S metastable state. It is further shown that the monotonic increase of the intensity of the Cd(II) 441.6 nm line with discharge current cannot be explained with the Penning collision process between He excited state atoms and Cd ground state atoms even if all the He excited states of n>or=3 and 2 3 , 1 P states are taken into account.