Yb3+、Ca2+离子共掺新型硼硅酸盐超快激光晶体的研究

Yb3+ ion doped crystals that typically have broad emission bands around 1 μm have been recognized as very attractive gain media for diode-pumped femtosecond (fs) oscillation and amplification. Yb3+ ion has a very simple electronic-level scheme involving only two manifolds 2F5/2 and 2F7/2, which consequently eliminates undesired effects such as excited-state absorption, cross relaxation, up-conversion, and concentration quenching. The re-absorption effect that lead to overlapping between absorption and emission spectra of Yb3+ ion doped crystals enlarges the pumping threshold of the laser system. Many kinds of substrate with different crystal field circumstance were studied to accommodate Yb3+ ion with strong coupling between electron and vibration. However, few studies have focused on the influence of lattice defect on the spectroscopic properties of Yb3+ ion. The structure character of LaBSiO5 is similar to that of borates and silicates to some extent, which could be doped with Yb3+ ion and Ca2+ ion simultaneously. This proposal aims at reducing the re-absorption effect of Yb3+ ion in LaBSiO5 crystal by controlled doping of Ca2+ ion.The substitution of Ca2+ ion for La3+ ion will introduce lattice defect into the LaBSiO5 crystal, and the concentration of lattice defect could be adjusted by the doping of Ca2+ ion. Crystal growth of Yb3+, Ca2+ ions co-doped LaBSiO5 crystal will be studied. Since LaBSiO5 melt incongruently, the top seeded solution method will be chosen to grow Yb3+, Ca2+ ions co-doped LaBSiO5 crystal. The flux, growth rate and morphology of the crystal will be focused on.The proposed research will also involve systematic study of the mechanical, thermal and optical properties of Yb3+, Ca2+ ions co-doped LaBSiO5 crystal.Existence of lattice defect will change the local vibration mode of substrate crystal, which will modify the crystal field circumstance of YbO9 polyhedron. Besides, the lattice defect could make the YbO9 polyhedron nearby distort and reduce its symmetry. These effects could be revealed by spectroscopic characterization of the crystal.Thus, the optical spectroscopy properties of Yb3+ and Ca2+ co-doped LaBSiO5 crystal will be studied by measurements of absorption, emission and low temperature emission spectra. Understanding how the Stark energy level splitting and Stokes energy shift of Yb3+ ion evolve is crucial to revealing the role of lattice defect in raditive transition of Yb3+ ion. Results and knowledge arising from the proposed research will also contribute to the pursuit of new femtosecond laser crystals.

Yb3+离子掺杂激光晶体是重要的超快激光增益介质，如何在保证Yb3+离子掺杂晶体宽带发射特性的同时有效抑制它的自吸收是目前该领域亟待解决的问题之一。加强晶场作用、增大Yb3+离子的斯托克斯位移是解决该问题的有效途径。LaBSiO5晶体同时具有部分硼酸盐和硅酸盐的结构特征，能够为Yb3+离子和Ca2+离子提供合适的物化环境。本课题拟向LaBSiO5晶体中同时掺杂Yb3+离子和Ca2+离子，通过调节Ca2+离子的掺杂浓度来控制晶格缺陷的含量。晶格缺陷能够改变基质晶体的局域振动模式，对与之相邻的YbO9多面体施加额外作用力，促使其发生畸变并降低该多面体的对称性，从而使其斯塔克能级分裂加剧。本课题通过Yb3+、Ca2+共掺LaBSiO5晶体的生长、光谱测试和晶场分析来阐明晶格缺陷对晶体中Yb3+离子发光行为的调控机制，对抑制Yb3+离子的自吸收效应和开发新型超快激光晶体具有理论意义与实际价值。

在LBSO 晶体的熔盐法生长过程中，我们重点探索了将混料设计思想应用于助熔剂探索尤其是复合助熔剂探索的可行性。利用相关实验设计软件，开发出一整套完善的多成分实验设计的实验方案设计及评估方法，并将其应用于系列激活离子掺杂钨钼酸盐晶体的生长。. 在Cr3+：MgWO4、Cr3+:Li2Mg2(WO4)3及Cr3+:Li2Mg2(WO4)3晶体的生长、光谱学及能级和晶场特性的研究方面，我们研究了这三种钨、钼酸盐晶体的助熔剂法生长规律，Cr3+离子在晶体中的能级分布情况以及掺杂之后晶体的光谱学性能，系统分析了异价掺杂之后激活离子在基质中所处的晶场情况及其对晶体光谱学性能的调控作用。. 在Yb3+:MgMoO4及Yb3+:MgWO4晶体的生长、光谱学及能级和晶场特性的研究方面，我们研究了Yb3+离子取代基质中的Mg2+离子之后晶体的生长规律、光谱学特性以及激活离子的能级分裂情况。. 在SrMoO4及Tm3+:SrMoO4等晶体的助熔剂法生长及光谱学性能研究方面，我们基于LBSO晶体的助熔剂法探索基础，成功地将混料设计思想应用于SrMoO4及Tm3+: SrMoO4晶体的助熔剂法生长，找到了适合用于生长SrMoO4及Tm3+: SrMoO4晶体的复合助熔剂体系，并得到了大尺寸高质量的Tm3+: SrMoO4晶体，以此为基础研究了该晶体的光谱学性能。Tm3+离子在该晶体中取代Sr2+离子，也属于异价掺杂情况。