为了研究固体激光器弛豫振荡的时间特性，针对高功率大口径Nd:YAG薄片激光器，从工作物质的能级结构和离子跃迁过程出发，采用四能级速率方程模型，综合考虑泵浦速率、损耗因子、温度等因素对激光器起振延迟时间的影响，建立了速率方程组，推导出激光起振延迟时间的数学表达式，模拟分析了泵浦速率、损耗因子、温度对激光起振延迟时间的影响。为验证理论分析结果，在kW级重复频率运行V型腔Nd:YAG薄片激光器上开展了实验研究。在泵浦电流分别为34，40，50，70 A时测量了反应谐振腔内光子数和反转粒子数变化的弛豫振荡曲线。并测量了在泵浦电流为30~80 A情况下的激光器起振延迟时间。实验结果表明起振延迟时间随泵浦速率的增加而减少，与理论分析结果一致。

Considering the four-level rate equations and the effects of pumping rate, loss factor and temperature, this paper theoretically deduced the expression of turn-on delay time for high power thin-disc laser. The numerical simulation results demonstrate the relationship of the pumping rate, loss factor and temperature versus the turn-on delay time. Corresponding experimental research was carried out on a kW-level repetition-frequency V-cavity Nd:YAG thin-disc laser. The relaxation oscillation curves illustrating the variations of photon number and inverted population were measured. The turn-on delay time was measured when the pump current was in the range of 30 A to 80 A. The experiment results show that the turn-on delay time reduces with the increase of pumping rate, which is consistent with the theoretical analysis.