掺稀土离子Yb：CaF2激光晶体光谱调控技术研究

Ytterbium ions doped laser crystal is of the first priority for direct diode laser pumped high power and high energy laser system. Yb:CaF2 crystal is a promising candidate for high repetition rate and high power laser system due to the advantages of obtainable large-sized crystal aperture (φ 440 mm) , high thermal conductivity (9.7 W/mK) and non-linear refractive index (0.43×10^-13 esu, 1/2 of that in phosphate glass). However, Yb:CaF2 crystal has the drawbacks of (1) low absorption and emission cross section leading to low gain cross section; (2) multi-peaks emission spectra although the full-width bandwidth (FWHM) of the emission spectra is large. This project will emphasize on the adjustable spectra from RE3+,Yb3+: Ca1-xSrxF2 (RE3+=Sc3+、Y3+、La3+、Gd3+、Lu3+) following the double-disordered structure from activation ions cluster and asymmetric host crystallographic sites. By designing and adjusting the local crystallographic sites of Yb3+ ions from large-sized and high quality RE3+,Yb3+: Ca1-xSrxF2 (RE3+=Sc3+、Y3+、La3+、Gd3+、Lu3+) crystal, it is highly expected to obtain smooth wide emission spectra with enhanced gain cross section for high power and high energy laser application.

面向二极管（LD）直接泵浦的超高峰值功率、大能量激光系统的发展要求，Yb3+离子是激光增益介质首选的激活离子。Yb:CaF2晶体具有尺寸大（最大尺寸超过φ440mm）、热导率高（9.7W/mK）、非线性折射率低（0.43×10^-13esu，小于磷酸盐玻璃的1/2）等综合性能优异，是目前最有应用前景的重频超高功率激光增益介质之一。但存在：1）吸收和发射截面偏小导致增益系数低；2）发射光谱尽管半高宽（FWHM）大，但光谱包络上仍存在多峰结构等缺点。本项目提出激活离子团簇结构和基质格位结构双无序的研究思路，拟通过碱土离子Sr2+和稀土离子（Sc3+、Y3+、La3+、Gd3+、Lu3+等）共掺的局域结构设计，调控其光谱特性，获得高的发射截面和平滑的宽带发射光谱。并制备出高光学质量的掺稀土离子Yb:CaF2激光晶体，实现在高功率、大能量激光领域的应用验证。

本研究按照原定计划进行探索，发展了一类具有宽光谱、高增益的新型稀土离子掺杂碱土金属氟化物激光晶体。采用改进温梯法制备得到3%Yb:CaF2-SrF2晶体，直径为70mm，透明无裂纹。通过Yb3+离子与稀土离子（如Y3+、Gd3+、La3+）共掺、Yb3+离子与碱金属离子（如Na+）共掺，研究了具有立方结构的碱土金属CaF2-SrF2、CaF2、SrF2晶体的晶体参数、热学与光学参数；通过调控局域结构与光谱特性，获得宽光谱、高增益激光晶体。采用激发波长980nm，15%Yb,20%Na:CaF2-SrF2晶体在1010nm处发射截面为6.52×10^-20cm^2、1036nm处发射截面为4.11×10^-20cm^2，发射光谱半高宽为70.3nm。形成技术总结报告1份。发表带项目编号标注学术论文8篇，其中SCI论文5 篇。申请发明专利4项，其中1项授权。本项研究为开拓新型高能量固体激光增益介质提供了支撑数据。