Velocity dependence of the performance of flowing-gas K DPAL with He and He/CH₄ buffer gases: 3D CFD modeling and comparison with experimental results

Accurate 3D computational fluid dynamics (CFD) modeling of flowing-gas K DPAL is presented, taking into account ionization and ion–electron recombination processes, ambipolar diffusion of K ions, and electron heating. Whereas in a static K DPAL with He buffer gas, the neutral K atoms in the lasing medium are depleted by these processes, the depletion can be mitigated by application of gas flow. The lowest gas velocity necessary for effective operation of a laser with He buffer is ∼500 m/s, and is much higher than previously estimated [Opt. Express 25, 30793 (2017)]. The predictions of the model for different He/CH₄ mixtures are presented and verified by comparing them with experimental results obtained at the Air Force Institute of Technology [“Kinetics of higher lying potassium states after excitation of the D₂ transition in the presence of helium,” dissertation (Air Force Institute of Technology, 2018)].