The nonlinear absorption (NLA) properties of potassium dideuterium phosphate crystals at 515 nm under different excitation laser intensities are investigated with the Z-scan technique. Two critical intensities are highlighted: the critical intensity for exciting the NLA and the critical intensity of the multiphoton absorption mechanism transition. Experimental results indicate the existence of defect states located in the band gap, which can be manipulated by varying laser intensity. A model based on the change of multiphoton absorption mechanism induced by the transformation of defect species is proposed to interpret the experiments. Modeling results are in good agreement with the experiment data.

中文翻译：

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强亚皮秒激光脉冲激发的 DKDP 晶体能带结构变化

采用Z扫描技术研究了不同激发激光强度下磷酸二氘钾晶体在515 nm处的非线性吸收(NLA)特性。突出显示了两个临界强度：激发 NLA 的临界强度和多光子吸收机制转变的临界强度。实验结果表明存在位于带隙中的缺陷态，可以通过改变激光强度来控制缺陷态。提出了一种基于缺陷物质转变引起的多光子吸收机制变化的模型来解释实验。建模结果与实验数据吻合较好。