用于直接产生3.0μm超快激光的Er3+掺杂ABC3O7系列晶体的设计、生长和性能研究

Mid-infrared wavelength ultrafast laser has found important potential applications in the fields of medicine, dectection, national defense and fundamental science researches etc.,which is the hot topic in the past decades, now it is just beginning to thrive in China. Nonlinear optical conversion techniques including OPO, difference frequency and OPA are the main methods to realize mid-infrared ultrafast laser currently. But as we know these optics system are very complicated, therefore,we bring forward to LD pump on one kind of novel Er3+:ABC3O7 (A=Ca,Sr,Ba; B=Y, La,Gd; C=Ga,Al) Melilite crystals to achieve 3.0 micron ultrafast laser directly. They have low phonon energy (around 560cm-1) and highly disordered structure, as a result the absorption and emission spetra of the active ion Er3+ inside are broadened extremely, which is very favorable for generation of the mode-locked ultrafast laser. In addition,they have high thermal conductivity,and high mechanical strength etc, and large-sized crystals with high optical quality can be grown by Czochralski technique. All these factors make Er3+:ABC3O7 crystals excellent candidates for 3.0μm ultrafast laser. In this project, we will design the crystal structure and elements,to target on 2~3 kinds ABC3O7 crystals and adjust Er3+ and the co-dopant sensitizing ions concentrations,then explore the crystal growth technique to obtain high-quality Er:ABC3O7 crystals, next study their spetral and laser characterizations.The emphasis is focused on study of the adjustment of the multi-locations in the hybrid crystals and the co-dopant sensitization ions through energy levels coupling theorically and experimentally, in order to further broaden their absorption and emission spectral width inhomogeneously. Finally,1~2 kinds of optimized Er:ABC3O7 crystals are obtained to carry on LD pumping and passive mode-locking with the excellent saturable absorber mirrors such as graphene and carbon nanotube, finally achieve high efficiency, short pulse and stable 3.0 micron ultrafast laser, for providing foundation for their application in mid-infrared ultrafast laser.

中红外超快激光在医疗、遥感、军事和科研等领域具有重要的应用前景。然而采用光参量振荡、差频、参量放大等非线性方法获得此波段的超快激光具有结构较为复杂的缺点。因此，本项目提出LD泵浦新型Er3+掺黄长石结构ABC3O7晶体直接实现3.0μm超快激光的方法。该体系的低声子能量(约560cm-1)和局部无序结构使Er3+的吸收和荧光光谱有显著展宽，非常有利于产生锁模超快激光。另外，该体系还具有热导率高、机械强度大及较易获得大尺寸优质单晶等优点。本项目从组成设计出发，从体系中筛选出2~3种ABC3O7晶型并调控Er3+及共掺敏化离子浓度，研究晶体生长工艺、光谱和激光性能，重点是通过混晶多格位调控和共掺敏化离子能级耦合的理论及实验研究，使谱线进一步非均匀展宽，优化出1~2种Er: ABC3O7晶体进行LD泵浦、被动锁模研究，实现高效率、窄脉宽、稳定运转的3.0μm超快激光输出，为其进一步应用奠定基础。

中红外超快激光在生物医疗、遥感、国防及基础科学研究等领域具有重要的应用，采用LD直接泵浦Er掺杂的低声子能、无序黄长石结构ABC3O7 (A=Ca,Sr,Ba; B=Y, La,Gd; C=Ga,Al) 晶体实现该波段激光具有重要的科学意义和潜在的应用价值。在本项目中，我们从ABC3O7体系中筛选出SrGdGa3O7、SrLaGa3O7、CaLaGa3O7、BaLaGa3O7、CaLaGa3-xAlxO7五种晶型，调控Er3+及共掺敏化离子浓度，获得几十种组分类型，研究多晶料合成和晶体生长工艺，采用提拉法分别生长出五个系列的Er单掺、Er及敏化离子双掺和三掺的晶体，系统研究其光谱和激光性能。提拉法生长获得晶体尺寸最大达到ф35mm×150mm，光学均匀性系数达到10-5量级。通过物化、热学和光谱性能表征，以及基于速率方程模型模拟激光性能的研究，该系列晶体可以实现连续或脉冲激光输出。该项目重点研究了晶体中稀土离子的浓度效应、共掺敏化离子能级耦合的敏化机理和能量传递机制、荧光动力学、混晶多格位调控引起的光谱性能的变化等。结果发现共掺合适浓度的敏化离子以及混晶多格位调控均使得吸收谱和中红外荧光谱线非均匀展宽，通过比较其光谱参数，优化出适合进行激光性能测试研究的最佳掺杂晶体类型为：Nd,Er:SrGdGa3O7、Yb,Er,Ho:SrLaGa3O7、Yb,Er,Pr:CaLaGa3O7等晶体。接下来对筛选出来的优质晶体进行了器件加工、激光腔型和膜系参数设计，采用LD泵浦和被动锁模进行了激光性能测试和研究，实现了高效稳定的中红外激光输出，激光输出波长2704nm，最高输出功率489mW，斜效率12.1%。这些成果为今后全固化中红外医疗激光器及产业化等方面奠定前期基础。在国内外学术刊物上发表论文55篇，授权发明专利2项，申请发明专利8项，培养研究生5名。