铌酸锂晶体电光调Q温度稳定性的关键影响因素及其机理研究

Lithium niobate (LiNbO3, LN) crystals are one of few practical crystals used for electro-optic (EO) Q-switching. They have the advantages of mature growth technology, no hygroscopic and large EO coefficients, which make them the preferred crystals in the field of optoelectronic application with wide temperature range. However, in practical application, the problems that the LN Q-switching performance has poor consistency at low temperatures and the cold performance for some crystals drop sharply are exposed. At present, there are few research on this issue, the reasons reported are various, and the mechanism for the deterioration of Q-switching performance at low temperature has not been studied. Thus, the results are unable to provide a guidance for the preparation of LN EO Q-switching crystals with high temperature stability.. This project will firstly study the cold Q-switching performance of the nominally pure LN and highly Mg-doped LN crystals under specified laser parameters and Q-switching modes, and select out the crystals with great difference, then contrastively and systemically explores their optical homogeneity, pyroelectric coefficient, conductivity, thermal refractive index coefficient and defect structures at low temperatures, ascertain the low-temperature defect structures of different LN crystals and their influence on properties. On these basis, combining with the theories of pyroelectric effect, EO effect, elasto-optic effect and thermo-optic effect, ascertain the key factors and related defect structure that affect the cold Q-switching performance. The research work of this project will lay the foundation for the preparation of LN EO Q-switching crystals with high temperature stability.

作为极少数可实用化的电光调Q晶体之一，铌酸锂（LN）晶体具有生长技术成熟、不潮解、电光系数较大等优势，是宽温度范围光电领域的首选晶体。然而，在实际应用中发现，LN晶体低温调Q性能一致性较差，部分晶体低温下调Q性能会大幅下降，严重影响了应用。目前，围绕这一问题的研究较少，报道的原因也各不相同，且未分析低温调Q性能变差的机理，从而无法为高温度稳定性LN电光调Q晶体的制备提供指导。. 本项目针对常用的名义纯及高掺镁LN晶体，首先在典型激光条件和调Q方式下，筛选出低温调Q性能差异较大的晶体，然后对其低温下的光学均匀性、热释电系数、电导率和折射率温度系数等性能参数以及低温缺陷结构进行系统对比研究，查明不同晶体的低温缺陷结构及其对性能的影响，在此基础上，结合热释电、电光、弾光、折射率温度效应等理论，探明影响低温调Q性能的关键因素及有关缺陷结构，为高温度稳定性LN电光调Q晶体的制备奠定基础。

铌酸锂（LN）晶体是极少数可实用化的电光调Q晶体之一，特别在宽温度范围光电领域是首选晶体，但在实际应用中发现其低温电光调Q性能一致性较差，部分晶体低温下调Q性能会大幅下降，影响因素和机理不明，严重影响了应用。本项目通过对名义纯及不同掺镁量LN晶体的低温电光调Q性能进行系统测试，筛选出了低温性能差异较大的晶体，通过表征低温光学均匀性，查明低温下晶体通光口径内各处双折射特性不同但分布具有规律性，不同晶体的双折射分布规律相同但变化程度不同，通过对比测量各晶体的热释电系数和电导率，结合理论分析探明了不均匀分布的热释电电场是影响低温调Q性能的主导因素，分析了其影响机理，查明各晶体电导率的差异造成了低温调Q性能的不同。在此基础上，采用热化学还原工艺，在碳酸锂粉末气氛下对名义纯LN晶体进行了退火还原处理，制备了电导率较高的LN电光Q开关，另外，为了克服热释电场的影响，还设计制备了沿Z轴加电场的双晶匹配LN电光Q开关，两种电光Q开关的低温调Q性能均明显提高。测试了各晶体样品的拉曼光谱和OH-吸收光谱，研究了不同晶体的缺陷结构，并结合晶体性能测试结果，分析了晶体缺陷对性能的影响。