In a pulsed discharge in a He‐Hg gas mixture favorable for laser oscillation of Hg ion at the green line, the temporal and spatial behavior of the population densities of Hg(63P2) and He(21S0) atoms has been studied experimentally. These reactants are thought to be responsible for the Penning‐like excitation process. It is found that the depression of the population of reactants coincides in space and time with the occurrence of the laser oscillation.