- Abstract The effects of heating, ionization, high electronic excitation and chemical reactions on the operation of diode pumped alkali lasers (DPALs) with a static, non-flowing gain medium are calculated using a semi-analytical model. Unlike other models, assuming a three-level scheme of the laser and neglecting influence of the temperature on the lasing power, it takes into account the temperature rise and losses of neutral alkali atoms due to ionization and chemical reactions, resulting in decrease of the pump absorption and slope efficiency. Good agreement with measurements in a static DPAL [B.V. Zhdanov, J. Sell, R.J. Knize, Electron. Lett. 44 (2008) 582] is obtained. It is found that the ionization processes have a small effect on the laser operation, whereas the chemical reactions of alkali atoms with hydrocarbons strongly affect the lasing power.