不同荷电态替位缺陷S_p对磷酸二氢钾激光损伤的影响

S substituting for P point defect-induced laser damage in KDP crystals

采用第一性原理方法计算了KH2PO4(KDP)晶体中各种荷电态的硫取代磷替位缺陷(SP)的几何驰豫构型及电子结构.讨论了该缺陷形成后电荷密度的重新分布、相应的电子态密度、能带结构等性质.主要结果为:虽然中性态、±1以及+2荷电态的Sp替位缺陷并没有在带隙中形成占据态,但它们削弱了SO4基团与周围原子的结合力,从而形成相对孤立的SO4基团,相对于无缺陷晶体而言,这种局域松散的结构有利于杂质原子的填隙,因而会间接地影响该材料的抗激光损伤能力.-2荷电态的Sp替位缺陷则在带隙中形成能够容纳4个电子的未占据态,使KDP晶体的带隙大大降低,提高了光吸收能力,降低了激光损伤阈值,同时该荷电态导致SO4四面体畸变严重,甚至使得周围的两个O—H键断裂,从而造成微结构的几何损伤.以上结果清楚地阐明了硫酸根影响KDP激光损伤阈值的微观物理背景.

In this paper, we present the ab initio calculations of S substituting for P point defects （Sp） in KDP crystal. The electronic structure and the relaxing configuration of Sp are studied. The properties of density of states and band structure of KDP with Sp are discussed. The Sp’s in neutral, ±1, and ＋2 charge states lead to the formation of an isolated SO4 in KDP and no defect state appearing in the energy gap. However, Sp in the -2 charge states induces defect states in the energy gap and therefore laser-induced damage threshold will be reduced.