四能级固体增益介质中长脉冲抽运光的吸收

The Absorption of Pumping Light in Four-level Solid State Medium Pumped with a Long Pulse

从激光介质中光能量的传输方程和速率方程出发,讨论了增益介质对抽运光的吸收问题。理论分析表明,只有在泵浦能量密度较小条件下(其量值因介质不同而不同)固体激光增益介质对抽运光的吸收才随吸收深度呈指数形式;当抽运光的能量密度增大到一定程度时,增益介质对抽运光的吸收随吸收深度由指数关系变为线性关系。把这个理论应用于 YAG晶体的模拟结果表明,当泵浦能量密度小于1.0×104 J·s-1·cm-2时,增益介质对抽运光的吸收随吸收深度近似指数形式;当泵浦能量密度大于1.0×105 J·s-1·cm-2时,在0.7 cm的吸收深度内,透过率与吸收深度的关系呈线性关系。

The theoretical solution of the pump light absorption in a 4-level solid state gain medium was presented by solving light transport and coupled rate equations of pump process in gain medium.It is shown that the absorption of pump light with respect to the depth in the solid medium is not simply a exponential function,when pump photon density is high enough,this absorption becomes a linearity with the absorption depth in the gain medium.The rule of the pump light absorption changing from expeonential to linearity was discussed.The simulation results for YAG crystal show that a rule of the pump light absorption is simplified to Beers formula only under the condition of I_0≤1.0×10~4 J·s^(-1)·cm^(-2),while I_0≥1.0×10~5 J·s^(-1)·cm^(-2) within absorption depth of 0.7 cm this rule is a linear function.