高光学质量BaGa4Se7晶体的生长及其中远红外激光输出性能研究

IR nonlinear optical (NLO) crystals have very important applications. BaGa4Se7 is a new IR NLO crystal discovered by us. Under the support of NSFC grant 51072203, we have obtained good quality crystal in the size of φ20 x 30 mm. Detailed physical property characterizations show that BaGa4Se7 possesses a number of advantages including large NLO coefficients（d11=27pm/V）, wide transparent range, high laser damage threshold, and large birefringence. In addition, preliminary OPA experiment have achieved high efficiency and high peak power "3-5μm" laser output. These results indicate BaGa4Se7 is very promising for practical application. Based on our previous work, we propose here to further optimize the growth of BaGa4Se7 and to thoroughly evaluate its performance in mid-far laser output. Our main work includes (1) obtaining crystals with larger size and improved quality and further measuring its physical properties. (2) thoroughly evaluating its performance in generating"3-5μm"、"6-7 μm" and"8-12μm"lasers by the optical parameter method (OPA and OPO) for the first time. (3) evaluating its performance in frequency doubling of the CO2 laser for the first time. As a result, we will finish the evaluation of application prospect of BaGa4Se7 crystal in generating mid-far IR lasers. We will also try to fabricate some devices suitable for practical application and hence make contribution to the development of our country.

红外非线性光学晶体具有非常重要的应用。BaGa4Se7是申请人发现的一种新型红外非线性光学晶体。在基金（No.51072203）资助下，我们已生长出φ20 x 30 mm的质量较好晶体，较详细的性质测试表明晶体具有非线性系数大（d11=27pm/V）、透光范围宽、损伤阈值较高和双折射较大等优点。初步光参量放大OPA实验已实现高效率、高峰值功率的"3-5μm"激光输出。因而BaGa4Se7具有良好的实用前景。 本项目拟在前期工作基础上，深入开展BaGa4Se7的生长和性能研究。包括：生长更大尺寸、更高质量晶体，进一步测定晶体性质；首次详细评估用光参量方法(OPA和OPO）实现"3-5μm"、"6-7 μm"和"8-12μm"波段激光输出性能；首次研究对CO2激光的倍频性能。 从而基本完成对BaGa4Se7在中远红外激光输出方面性能的全面评估，并力争做成器件得到应用，为国家发展作出贡献。

BaGa4Se7是由本项目申请人发现的一种新型红外非线性光学晶体。该晶体具有大的非线性光学系数（d11 = 27 pm/V）、宽的透光范围(0.47-18 µm)，较高的激光损伤阈值和较大的双折射。可实现高功率、大能量的红外激光输出。.本项目在前期工作的基础上，深入开展BaGa4Se7的生长和性能研究。在项目的资助下，我们掌握了用双温区法大规模合成BaGa4Se7多晶原料的合成方法和BaGa4Se7晶体的坩埚下降法生长工艺 （坩埚形状、温场、下降速度等）, 获得了Φ40×150 mm 的外形完整的大尺寸，高质量的晶体，并测试了BaGa4Se7晶体的二阶非线性光学系数，研究不同的退火方法，发现当使用BaGa4Se7粉末作为退火源时，通过双温区退火法可获得迄今为止最佳的退火效果。经过双温区退火后，BaGa4Se7的透过率显著提高。.在此基础上，我们以波长2.09 μm，重频500 Hz，最小脉宽约为27 ns，光束质量因子约为1.18的激光泵浦BaGa4Se7晶体，实现最大输出功率约为1.55W (脉冲能量3.10 mJ/pulse)，斜率效率约为19.9 %，参量光脉宽18ns，波长调谐范围3.5~5.2 µm。还研制出以Cr:Er:YSGG，2.79 μm激光为泵浦光源，设计OPO双谐振，在信号光波长为4.57 μm，闲频光波长为7.16 μm时，实现了OPO输出能量最大2.1 mJ，光转换效率为11.7 %，斜效率高达30.4 %。并首次研制出采用2.09 μm的Q开关Ho:YAG激光泵浦BaGa4Se7晶体的高效率可调谐的8-9μm的长波红外光学参量振荡器，获得了最大平均空闲输出功率314 mW，相应的斜率效率为7.44 ％，量子斜率效率为32 ％，此外，还实现了8-9 μm的调谐范围。. BaGa4Se7的物化性能和一系列的激光实验结果表明BaGa4Se7是一种综合性能优秀并有重要实用价值的新型红外非线性光学晶体。