基于微结构工程的YAG基激光陶瓷品质提升研究

Since the first demonstration of high efficient Nd:YAG ceramic laser in 1995, rapid progress has been made on the ceramic laser materials and ceramic lasers. However, ceramic is intrinsically different from a sing le crystal by that it is polycrystalline. Despite of the fact that there has been significant progress on the ceramic laser materials and ceramic lasers in the past decade, a number of questions such as how is the effects of the polycrystalline on the laser beam properties of a ceramic laser, and how does the existence of the grain boundaries affect the performance of a ceramic laser, are so far still not clearly addressed. Further detailed experimental studies identified that the grain boundaries of a ceramic laser gain medium could introduce doping non-uniformity into the ceramic laser materials. As a result of the doping segregation more doped ions are in the grain boundary region than in the grain. The doping non-uniformity further causes that the refractive index of the laser ceramic becomes non-uniform, which in return causes extra scattering loss. The proposed project aims to investigate experimentally the relationship between the grain boundary induced doping non-uniformity and the grain microstructure, ceramic fabrication processes parameters, and the doping concentrations. Here we propose a novel dopant segregation characterization method based time resolved photoluminescence spectra. Through the experimental research we aim to identify an optimized ceramic fabrication processing so to fabricate laser ceramics with the desired properties.

自1995年Ikesue博士制备出世界上首块高效激光陶瓷以来，陶瓷激光材料和陶瓷激光器取得了迅猛发展。然而，陶瓷的多晶态特征使得其与单晶存在本质不同。陶瓷增益介质的晶界可能会在陶瓷激光材料中引入不均匀掺杂--掺杂离子偏析的结果使得晶界处比晶粒内部的掺杂离子浓度要高。这种不均匀掺杂进而导致激光陶瓷的折射率不均一，并反过来会产生额外的散射损耗，这可能是目前陶瓷散射损耗仍略高于高质量单晶的原因。本课题拟从实验出发探索晶界引入的非均一性和晶界微结构、陶瓷制备工艺参数和掺杂浓度之间的关系。创新的提出采用时间分辨微区荧光光谱对激光陶瓷进行 3D 扫描，直观准确地研究激光陶瓷中掺杂引入的非均匀现象, 给出激光陶瓷由掺杂引入不均匀性的3D信息，找出不同种类激光陶瓷理想的微结构参数如平均晶粒尺寸、晶界厚度等，并反馈优化激光陶瓷制备的工艺参数，以制备出具有理想结构的激光陶瓷材料。

高质量激光透明陶瓷材料可以弥补激光晶体和激光玻璃的不足，这使得陶瓷激光材料和陶瓷激光器取得了迅猛发展。然而，陶瓷的多晶态特征使得其与单晶存在本质不同。陶瓷增益介质的晶界可能会在陶瓷激光材料中引入不均匀掺杂。这种不均匀掺杂进而导致激光陶瓷的折射率不均一，并反过来会产生额外的散射损耗，这可能是目前陶瓷散射损耗仍略高于高质量单晶的原因。本项目制备了一系列不同稀土离子掺杂、不同晶粒尺寸的YAG基透明陶瓷。通过空间分辨共聚焦Raman光谱证实了稀土掺杂离子在YAG透明陶瓷中的偏析现象，并给出激光陶瓷由晶界引入的掺杂不均匀性的3D信息。通过优化陶瓷的制备工艺参数，制备出高质量的稀土掺杂YAG透明陶瓷，其透过率达到了理论值，散射损耗在千分之一水平。成功实现了Ho:YAG和Ho:LuAG透明陶瓷的激光输出。