1. Introduction . Diode-pumped alkali lasers (DPALs) are optically pumped, near-infrared, continuous-wave (CW) gas lasers. A vaporized alkali metal—such as potassium, rubidium, or cesium—mixed with helium buffer gas at nearly atmospheric pressure serves as the active medium. A DPAL is optically pumped by a narrow-band laser diode at the D 2 transition, and it lases at the D 1 transition. Figure? 1 shows an energy diagram and the transition paths of a Cs DPAL. In a Cs DPAL, methane ...