研究了用于三倍混频的Ⅱ类DKDP晶体在35 ps，850 ps和7.6 ns三种不同脉宽355 nm波长激光作用下的损伤特性。实验对比分析了损伤阈值、概率和损伤针点形貌、尺寸和密度，并根据损伤阈值及概率得到前驱体阈值及密度。结果表明，前驱体的激光能量吸收量与脉宽线性相关。35 ps激光作用下DKDP有一种前驱体吸收激光能量形成熔融状损伤针点。850 ps激光作用下有两种前驱体吸收激光能量并产生力学破坏形成中心熔融四周断裂的损伤针点。7.6 ns激光作用下只有一种前驱体吸收激光能量，并且形成的损伤针点与850 ps对应的损伤针点有相同特征。

This paper researches on laser damage characteristics of Ⅱ-type DKDP crystals used for nonlinear frequency conversion of third harmonic under 355 nm laser with 35 ps, 850 ps and 7.6 ns pulse duration. The damage threshold, probability and the damage pinpoints morphology, density, size under different pulse duration are compared and analyzed. The results show that the laser energy absorption of the precursors is linearly related to the pulse duration. Under 35 ps laser, one type of precursors absorbs laser energy, which results in melting damage pinpoints. Under 850 ps laser, two types of precursors absorb laser energy and generate mechanical response form damaged pinpoints made of melting center point and surrounded by cracks. Under 7.6 ns laser, only one type of precursors takes effect and shares the same pinpoints characteristics with 850 ps laser.