Dependence of the optically pumped Ne*-He lasing threshold on the position of the pump beam

The dependence of pumping thresholds of the optically pumped Ne*-He laser on the position of the pump beam between the electrodes was obtained for
$\mathrm{s}_{5}\rightarrow \mathrm{p}_{9}$
or
$\mathrm{s}_{5}\rightarrow$
p
8
pumping transitions. It was found that pumping thresholds strongly depended on the position of the pumping beam, and the minimum is reached near the center between the electrodes. The ratio of p
8
/p
9
thresholds at their minima is 13.