Measurement of the Plasma Environment in a Rb DPAL

Diode-pumped alkali lasers (DPAL) offer the potential for scaling to high output powers required for directed energy weapons systems. As power-scaling studies have progressed, increasing concern has emerged about uncertainty in the roles of higher-lying states and the degree of ionization, and their effects on device performance. Ionization by multi-photon absorption and collisional energy pooling may result in a plasma that reduces optical efficiency, increases gas heating, and diminishes beam quality. To address these concerns, advanced diagnostic concepts are required for measurements of the key plasma parameters, electron density and electron energy distribution function (EEDF), in optically pumped Rb/He mixtures representative of high-power DPAL systems. Physical Sciences Inc. (PSI) and its STTR partner, the Air Force Institute of Technology (AFIT), propose to develop a combination of advanced, high-sensitivity diagnostics for direct measurements of plasma electron density and EEDF. The Phase I effort will conduct experimental measurements using microwave interferometry at PSI and Stark broadening of Rb transitions at AFIT, together with theoretical and model-based analyses of electron number density and EEDF, to create a detailed Phase II plan to determine the plasma properties in a surrogate Rb DPAL system. Approved for Public Release | 22-MDA-11339 (13 Dec 22)