紫外低吸收GdAl3（BO3）4晶体生长和266nm激光输出研究

GdAl3(BO3)4 (GAB) crystal has been discovered since the 1960s, which was mainly studied as a self-frequency-doubling material for laser application. So far it is rarely reported that GAB is studied as a nonlinear crystal in the ultraviolet applications,because the UV cut-off edge of GAB crystal grown from molybdate flux is about 300nm. Recently, we explored a new flux system(Metal oxides-B2O3- Fluoride). The UV cut-off edge of GAB crystal grown from the new flux is about 175nm and GAB large size crystal growth is easier than YAl3(BO3)4 base on the new flux system. The powder SHG of GAB is about 3.5 times of KDP and laser damage threshold is 11.31GW/cm2. GAB grown crystal exhibits good chemical stability, free of moisture and hygroscopy, and excellent mechanical properties. Therefore, GAB is able to use as a nonlinear optical crystal in the ultraviolet. This study includes exploration and optimization of flux system for low UV absorption GAB growth, crystal growth process, and linear and nonlinear optical characterization. It is the first time to achieve fourth harmonic (266nm) laser output through using GAB crystal. As a result, GAB crystal is possible to use as a new alternative four-frequency-doubling crystal material in the Nd: YAG (1064nm) laser.

GdAl3(BO3)4(GAB)晶体自1960年代被发现以来，研究集中在稀土掺杂GAB晶体生长和其在激光自倍频方面的应用。由于通常采用钼酸盐助熔剂生长的GAB晶体紫外截止边在300nm左右，到目前为止，GAB作为应用于紫外短波段非线性光学晶体研究很少。近期，我们探索出一种"金属氧化物-B2O3-氟化物"助熔剂体系，生长的GAB晶体紫外截至边在175nm，且较同结构类型YAl3(BO3)4更易生长出大尺寸晶体。GAB晶体的粉末倍频效应约为3.5倍KDP且能够实现相位匹配，GAB晶体不潮解、硬度大，抗激光损伤阈值约为11.31GW/cm2，使其在紫外短波段应用成为可能。本研究包括紫外低吸收GAB晶体的助熔剂体系探索与优化、单晶生长，线性与非线性光学性能表征等，将首次实现GAB晶体的Nd:YAG(1064nm)激光266nm输出。GAB晶体可能成为有应用前景的四倍频非线性光学晶体。

在“Li2O-B2O3-NaF”新助熔剂体系基础上，通过调节各个助熔剂之间的摩尔比以及助熔剂与溶质的摩尔比，根据晶体生长实验确定出了合适的摩尔比为Gd2O3 : Al2O3 : H3BO3 : Li2CO3 : NaF =1 : 3 : 5～7 : 1～3 : 1～3，在此基础上成功生长出了尺寸为181835mm3的高质量GAB晶体。通过测定单晶在紫外区域的透过率，发现晶体的紫外截止边在175nm。通过粉末倍频实验，确定GAB晶体的NLO系数是KDP的3.5倍。同时也测量了晶体的折射率，根据折射率数据，拟合了晶体的Sellmeier方程，拟合结果能够与数据吻合；根据方程计算了晶体的相匹配的相关参数，结果表明晶体的最短二倍频波长为248nm，在理论上能够实现266nm输出。根据晶体的结构确定了激光实验中的晶体器件参数，首次实现了532nm到266nm的激光倍频输出。综合来看，GAB晶体具有适中的双折射率、宽的透过范围（175nm-3000nm）、较大的NLO系数、较高的激光损伤阈值，以及良好的物化性质。因此，GAB晶体具有适合于Nd：YAG（1064nm）四倍频的实际应用的潜质。