“…For the proper assignment of the intermediate levels in such two step excitations, precise excitation transitions and molecular constants of the corresponding electronic states are necessary, which motivates further spectroscopic studies of electronic states implied in the pump laser transition. Moreover, because of its simple molecular structure, ease of production, stability at a precise pressure and temperature for a long time, and favourable absorption and emission cross sections, investigation of optically pumped laser (OPL) sodium dimers is of special interest (see, for example, [18][19][20][21][22][23][24]). Alkali dimer lasers are not only of practical use in conventional molecular spectroscopy but furthermore allow studies of fundamental processes such as the parametric interaction of two laser fields with a molecule, the saturation of molecular transitions, and the influence of collisions on the line shape and intensity of the laser transitions.…”