基于2μm以上波段高重频应用的新型电光晶体Na3La9O3(BO3)8的电光性能及其应用基础研究

Electro-optical crystals are the key materials for the electro-optical Q switch, electro-optical modulation, and electro-optical deflection, which have very improtant applications in the rapid development of modern optoelectronics and all solid-state laser technologies. High peak power, short pulse, and high average power lasers are needed in mordern micro-machining, medical, and military applications. In order to obtain higher peak power, shorter pulse width, it is urgently needed to develop new electro-optical crystal which are favorable to the high repetition frequency and high power applications above 2 μm wavelength range. A new promising nonlinear optical (NLO) crystal, Na3La9O3(BO3)8 (abbreviated as NLBO)，was discovered in our group (US Patent No: US6,921,498 B2, China Patent: ZL01134393.1). NLBO crystal has excellent properties of frequency conversion. NLBO crystal has relatively larger electro-optical coefficient (γ22(NLBO)=2.3 pm/v), wide optical transparency range (220-2500 nm), high refractive indices and small thermal refractive index coefficients, high thermal conductivity and low thermal expansion coefficients, high laser damage threshold (5GW/cm2), and good mechanical properties (Mohs hardness 7). More importantly, NLBO crystal is stable in atmosphere and free from moisture, which make its devices without any protections to be stably used for long time at room temperature. NLBO crystal meet many basic requirements of the practical application of electro-optical crystal, and the electro-optical performances are comparable to commercial BBO crystal. This project aims at to develop the electro-optical applications of NLBO crystal. The key growth technology of the NLBO crystals with large size and high optical quality will be achieved. The as-grown can be used to fabricate electro-optical devices. The electro-optical properties will be investigated systemically. This project will be of significance to promoting the development of NLBO crystal in electro-optical application field, which will maintain the competitive advantage and extend independent intellectual property rights of NLBO crystal.

电光晶体是光电子学和激光技术中实现光电信号相互转换、控制或调制的关键材料，可满足材料加工、医疗、军事等应用对高重频、高峰值功率和窄脉宽激光的迫切需求。目前适合2μm以上波段高重频高功率应用的电光晶体依然稀缺，仍需发展综合性能良好的电光晶体。Na3La9O3(BO3)8(NLBO)是我们发现并拥有完全自主知识产权的新型非线性光学晶体，不仅具有良好的频率变换性能，而且还因其具有电光系数大、透光范围宽、折射率大、温度效应小、损伤阈值高、完全不潮解等优点，满足作为实用电光晶体的基本要求，显示出与BBO相当的电光性能，是一种亟待开发的新型电光晶体。本申请目标是发展NLBO的电光应用，特别是在2μm以上波段高重频方面的应用，为此开展大尺寸高光学质量晶体生长、电光器件优化设计制作、电光性能表征等研究。本项目研究将获得NLBO在电光应用领域的原创性成果，对扩大NLBO的研究优势，推进其实用化具有重要意义。

Na3La9O3(BO3)8 (NLBO)是我们发现并拥有完全自主知识产权的新型非线性光学晶体，不仅具有良好的频率变换性能，而且还因其具有电光系数大、透光范围宽、折射率大、温度效应小、损伤阈值高、完全不潮解等优点，满足作为实用电光晶体的基本要求，显示出与BBO相当的电光性能，是一种亟待开发的新型电光晶体。本项目旨在探索综合性能更佳的新助熔剂体系，通过相平衡关系研究，确立适合NLBO晶体生长的组分及其比例，通过改造晶体生长装置，优化生长工艺条件，获得较大尺寸高光学质量NLBO晶体；研究晶体缺陷及其与生长工艺条件的关系，寻求提高晶体质量的有效途径；测量晶体透过率、折射率、抗光损伤阈值等基本性质；制备晶体器件，评估其应用前景。.通过本项目研究，探索出挥发性小、粘度低的适合生长NLBO晶体的新助熔剂体系BaO-MoO3，通过相平衡关系的研究，确定了生长组分的摩尔比NLBO:BaO:MoO3=1:0.8:0.4；改进了生长炉结构，构建出大范围恒温生长区间，通过优化旋转速率、降温速率、退火程序等关键工艺参数，生长出40×35×20 mm3的完整透明未开裂的晶体；研究了生长台阶、空洞、解理、气相和液相包裹体缺陷的初步成因及其克服途径；测量了晶体的弱吸收、抗光损伤阈值、折射率及其温度系数、电光系数、介电常数等基本性质；加工出4×4×10 mm3三倍频器件，实现了108 mW的355 nm激光输出。项目执行期间，还发现了多种新型非线性光学晶体，其中Na3Y3(BO3)4属六方晶系，P63mc空间群，粉末倍频效应强度为2.4倍KDP，紫外截止边为253 nm；LiGaP2O7属单斜晶系，P21空间群，粉末倍频效应强度约为1.2倍KDP，紫外截止边为271 nm；Rb7SrY2B15O30属三方晶系，空间群R32，单晶粉末样品倍频测显示其倍频效应强度为1.2倍KDP，但不能实现相位匹配。.本项目发展的NLBO晶体新的生长体系，将有助于获得大尺寸高光学质量NLBO晶体，为其实际应用奠定良好基础。这对于拓展NLBO晶体的应用领域，扩大我国在NLBO晶体研究方面的优势，为全固态激光技术的发展提供新的备选晶体材料，具有重要意义。新发现的非线性光学晶体，在紫外区也具有潜在应用价值，对于深入理解结构与性能的关系，拓展非线性光学晶体的研究范围具有积极意义。