Recently it was observed that adding a small amount of methane to the He buffer gas of a static potassium diode pumped alkali laser (K DPAL) increases considerably the laser power. Further increase in the amount of methane leads to a moderate decrease in power. In the present work the effect of methane addition was investigated theoretically applying a 3D computational fluid dynamics (CFD) and potassium kinetics model, which was supplemented by the analysis of the electron temperature and K ion ambipolar diffusion. It was found that for a pure He buffer the K DPAL power is lower than for ${\rm He}/{{\rm CH}_4}$ mixtures due to slow ion-electron recombination and high electron temperature exceeding 3000 K. The high electron temperature in pure He results in fast ambipolar diffusion of K ions to the wall and depletion of the neutral K atoms in the lasing region. These effects are mitigated when methane is added to the buffer gas. The calculated results for the normalized laser power are in satisfactory agreement with the experimental ones.

中文翻译：

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静态K DPAL性能对向He缓冲气体中添加甲烷的依赖性：3D CFD建模并与实验结果进行比较

最近，观察到向静态钾二极管泵浦碱金属激光器（K DPAL）的He缓冲气体中添加少量甲烷会大大提高激光功率。甲烷量的进一步增加导致功率适度降低。在本工作中，使用3D计算流体动力学（CFD）和钾动力学模型从理论上研究了甲烷添加的效果，并通过分析电子温度和K离子双极性扩散对其进行了补充。发现对于纯He缓冲区，K DPAL功率低于$ {\ rm He} / {{\ rm CH} _4} $由于缓慢的离子电子重组和超过3000 K的高电子温度而产生的混合物。纯He中的高电子温度导致K离子快速双极性扩散到壁上，并耗尽了激光区域中性K原子。当将甲烷添加到缓冲气体中时，这些影响会减轻。归一化激光功率的计算结果与实验结果令人满意。