Measurement of the concentration of metastable helium atoms in a single pulsed discharge

The concentration of metastable helium atoms was measured during the pulse of a laser and in afterglow. The concentration of metastable helium atoms in the 2(1)S(0) and 2(3)S(1) states reaches a maximum at the beginning of the excitation pulse which is independent of the pulse duration. The concentration of 2(3)S(1) atoms exhibits a second sharply defined maximum during afterglow, the position of which is dependent on the length of the excitation pulse. The absolute concentration in the afterglow rises with increasing pulse length. The presence of residual plasma conditions the destruction of metastable helium atoms in the following excitation pulses.