Effects of Plasma Formation on the Cesium Diode (DPAL) and Excimer (XPAL) Pumped Alkali Laser

Diode pumped alkali lasers (DPALs) and excimer pumped alkali lasers (XPALs) are being investigated as a means to convert optical pumps having poor optical quality to laser radiation having high optical quality [1]. DPALs sustained in Cs vapor are pumped on the D$_{\mathrm{2}}$(852.35 nm), Cs(6$^{\mathrm{2}}$S$_{\mathrm{1/2}})\to $ Cs(6$^{\mathrm{2}}$P$_{\mathrm{3/2}})$, transition and lase on the D$_{\mathrm{1}}$(894.59 nm) transition, Cs(6$^{\mathrm{2}}$P$_{\mathrm{1/2}})\to $ Cs(6$^{\mathrm{2}}$S$_{\mathrm{1/2}})$. Collisional mixing (spin orbit relaxation) of the Cs(6$^{\mathrm{2}}$P$_{\mathrm{3/2}})$ and Cs(6$^{\mathrm{2}}$P$_{\mathrm{1/2}})$ levels is a key part of this three-level (in fact, a quasi-two-level) laser scheme. In the five-level XPAL pumping scheme, the CsAr(B$^{\mathrm{2}}\Sigma ^{\mathrm{+}}_{\mathrm{1/2}})$ state is optically pumped by 836.7 nm pulses, which later dissociates and produces Cs(6$^{\mathrm{2}}$P$_{\mathrm{3/2}})$. As in DPAL, a collisional relaxant transfers the population of Cs(6$^{\mathrm{2}}$P$_{\mathrm{3/2}})$ to Cs(6$^{\mathrm{2}}$P$_{\mathrm{1/2}})$, which enables lasing on D$_{\mathrm{1}}$ transition. A first principals global computer model has been developed for both systems to investigate the effects of plasma formation on the laser performance. Argon is used as a buffer gas and nitrogen or ethane are used as a collisional relaxant at total pressure of 600 Torr at temperatures of 350-450 K, which produces vapor pressures of Cs of \textless 0.1 Torr. In both systems, a plasma formation in excess of 10$^{\mathrm{14}}$ - 10$^{\mathrm{16\thinspace \thinspace }}$cm$^{\mathrm{-3}}$ occurs, which potentially reduces laser output power by electron collisional mixing of upper and lower laser levels [2]. [1] W.F. Krupke, et. al., Opt. Lett. \textbf{28} 2336 (2003). [2] B.D. Barmashenko, et. al. Opt. Comm. \textbf{292}, 123 (2013).