Residual infrared absorption is a key problem affecting the laser emission efficiency of Ti:sapphire crystal. In this paper, the origin of residual infrared absorption of Ti:sapphire crystal is systematically studied by using the first principles method. According to the contact conditions of O octahedron in the crystal structure of ${\mathrm{Al}}_2{\mathrm{O}}_3$, four ${\mathrm{Ti}}^{3+}-{\mathrm{Ti}}^{3+}$ ion pair models and three ${\mathrm{Ti}}^{4+}-{\mathrm{Ti}}^{3+}$ ion pair models were defined and constructed. For what we believe is the first time, the near-infrared absorption spectra consistent with the experimental results were obtained in specific theoretical models. The electronic structures, absorption spectra, and charge distributions calculated show that the line-contact ${\mathrm{Ti}}^{3+}-{\mathrm{Ti}}^{3+}$ ion pair with antiferromagnetic coupling and the face-contact ${\mathrm{Ti}}^{4+}-{\mathrm{Ti}}^{3+}$ ion pair are two main contributors to the residual infrared absorption of Ti:sapphire, while some other ion pair models provide a basis to explain more complex residual infrared absorption.

中文翻译：

---

钛蓝宝石激光晶体残余红外吸收的理论研究

残余红外吸收是影响钛蓝宝石晶体激光发射效率的关键问题。本文采用第一性原理方法系统地研究了钛:蓝宝石晶体残余红外吸收的起源。根据O八面体在晶体结构中的接触条件${铝}_2{\mathrm{哦}}_3$, 四 ${钛}^{3+}-{钛}^{3+}$ 离子对模型和三个 ${钛}^{4+}-{钛}^{3+}$定义并构建了离子对模型。我们认为这是第一次在特定的理论模型中获得与实验结果一致的近红外吸收光谱。计算的电子结构、吸收光谱和电荷分布表明，线接触${钛}^{3+}-{钛}^{3+}$ 具有反铁磁耦合和面接触的离子对 ${钛}^{4+}-{钛}^{3+}$ 离子对是 Ti:sapphire 残余红外吸收的两个主要贡献者，而其他一些离子对模型为解释更复杂的残余红外吸收提供了基础。