Regenerative Soot-VII: Population inversion of He I and Ne I in   regenerative sooting discharges
  The mechanisms for population inversion among the excited states of He I and Ne I in regenerative sooting discharges have been investigated as a function of the geometry and the physical parameters of the graphite hollow cathode sources. The effect of the state of sooting of the hollow cathode, the gas pressure and the role of the cycling of the discharge current idis on the population inversion of the excited He I and Ne I levels have been investigated. 
Sajid Hussain, A Aleem, Rahila Khalid, S D Khan, A Ellahi, S A Janjua   and Shoaib Ahmad
cond-mat.mes-hall