The diode-pumped rare gas laser (DPRGL) has been suggested as a potential high-gain, high-energy laser which requires densities on the order of 10<sup>13</sup> cm<sup>−3 </sup>at pressures around 1 atmosphere for efficient operation. Argon 1s<sub>5</sub> number densities have been measured in micro-hollow cathode discharges with electrode gaps of 127 and 254 μm and hole diameters from 100-400 μm. The dependency of the metastable argon (1s<sub>5</sub>) density on total gas pressure, electrode gap distance and hole diameter were explored. The measured densities were all in the range of 0.5 − 2 × 10<sup>13</sup> cm<sup>−3</sup> with the 400 μm hole diameters being the lowest.
Fine-structure mixing cross-sections for the alkalis in collisions with the rare gases are reviewed. Included in the review are all the rare gases in collisions with all of the first excited state of the alkalis, the second excited state for K, Rb and Cs and the third excited state for Rb and Cs. The cross-sections are converted to probabilities for energy transfer using a quantum-defect calculated cross-section and are then presented as a function of adiabaticity. The data shows a clear decreasing trend with adiabaticity but secondary factors prevent the probabilities from decreasing as quickly as expected. Polarizability is introduced as a proxy for the secondary influences on the data as it increases with both rare gas partner and alkali excited state. The polarizability is shown to cause the probability of fine structure transition to be higher than expected. An empirical model is introduced and fit to the data. Future work will develop a model using time-independent perturbation theory in order to further develop a physical rational for the dependence of fine structure cross sections on adiabaticity and to further understand the secondary influences on the probability for fine structure transition.