Detailed analysis of kinetic and fluid dynamic processes in diode-pumped alkali lasers

Abstract

Kinetic and fluid dynamic processes in diode-pumped alkali lasers (DPALs) are analyzed in detail using a simple, semi-analytical model, applicable to both static and flowing-gas devices. Unlike other models, it takes into account the effects of temperature rise, excitation of neutral alkali atoms to high lying electronic states and their losses due to ionization and chemical reactions, resulting in a decrease in pump absorption, slope efficiency, and lasing power. Effects of natural convection in static DPALs are also taken into account. The applicability of the model is demonstrated in Cs DPALs by (1) obtaining good agreement with measurements in static [Electron. Lett.44, 582 (2008)] and flowing-gas [Quantum Electron.42, 95 (2012)] DPALs, (2) predicting the dependence of power on the flow velocity in flowing-gas DPALs, and (3) checking the effect of using a buffer gas with high molar heat capacity and a large relaxation rate constant between the P3/22 and P1/22 fine-structure levels of the alkali atom. The power strongly increases with flow velocity and by replacing, e.g., ethane by propane as a buffer gas, the power may be further increased by up to 30%; 7 kW is achievable in a small-scale laser with 10  cm3 of propane for a 20 kW pump at a flow velocity of 20 m/s..