Influence of the lower levels population on the oscillation of the green lines in He-Cd laser

A study of the influence of the lower levels population on the saturation of the green lines output power of a hollow cathode He-Cd laser is presented. Results from measurements show that limitation of the output power of the green Cd lines at higher Cd pressure is due not only to the decrease of ground state He ions population, but also to processes populating the lower laser level. These can be direct electron, impact, or Penning processes between He metastable atoms and ground state atoms and helium molecular ions