新型拉曼激光晶体Ca3(BO3)2的大尺寸生长及高能量输出

Stimulated Raman scattering (SRS) is an important branch in the field of nonlinear optics, as an effective method to obtain new wavelength coherent light source. In the past, SRS research is mainly focused on the gas, liquid medium. In recent years the international solid state Raman laser technologies have developed rapidly, which use the optical fiber and crystal as the work medium. So far, the typical SRS crystals which have been studied include diamond, nitrate, tungstate, vanadate, molybdate and iodate, etc.. Recently, we have realized the broadband stimulated Raman scattering of Ca3(BO3)2 crystal for the first time. We found this crystal is an excellent, all round SRS medium, because it possesses many advantages such as easy growth, low cost, short ultraviolet cut-off edge, large Raman gain coefficient, and high laser damage threshold. Based on this research, the present project will grow the Ca3(BO3)2 crystal with large size, research their basic, SRS, laser, and self-Raman laser properties systematically, and complete the optimization design of related optical functional devices. This project can fill the research gap of SRS, improve the SRS theory, promote the further development of crystaline Raman laser field, and will provide a new class SRS materials and devices which have important application values to our society.

受激拉曼散射（SRS）是非线性光学领域的重要分支，是获得新波长相干光源的有效手段之一。过去，SRS研究主要集中于气体、液体介质，近年来国际上固体拉曼激光技术迅猛发展，使用的介质主要为光纤和晶体。到目前为止，人们已经研究过的典型的SRS晶体有金刚石、硝酸盐、钨酸盐、钒酸盐、钼酸盐和碘酸盐等。最近，我们首次实现了三方硼酸盐晶体（Ca3(BO3)2）的宽波段SRS，发现该晶体具有易生长、成本低、紫外截止边短、拉曼增益系数大、抗光伤阈值高等优点，是一种综合性能优良的SRS晶体。以此为基础，本项目提出生长大尺寸优质Ca3(BO3)2晶体，对其制备工艺、基本性质、SRS性能进行系统研究，完成相关光功能器件的优化设计，实现大能量拉曼激光变频。本课题能填补硼酸盐SRS的研究空白，丰富晶体SRS理论，促进固体拉曼激光领域的进一步发展，有望为社会提供一类新型的、大尺寸有重要应用价值的SRS材料和器件。

激光是近代物理学领域重要的发明之一，具有单色性好、相干性强、亮度高、传播距离远等优势，在通讯、医疗、工业、农业、娱乐、生物、国防和科研等领域拥有广泛的需求。拉曼晶体在激光的变频技术中具有重要应用，通过晶体的受激拉曼散射效应，可以拓展激光器的输出光谱范围。本课题提出了一种新型拉曼激光晶体Ca3(BO3)2，它在结构上具有高密度、孤立和一致性排布的[BO3]3-功能基团，这种结构显示出较强的拉曼性能。此外，Ca3(BO3)2晶体具有高的抗光损伤阈值、宽的紫外到近红外透过范围、容易大尺寸制备和低的制造成本等优势。本课题主要研究了Ca3(BO3)2晶体的提拉法生长技术、基本光学性质、热学性质、自发拉曼光谱、拉曼增益系数、抗激光损伤特性、受激拉曼散射和拉曼激光器件设计，成功实现Ca3(BO3)2晶体深紫外到近红外宽波段的大能量拉曼激光变频。本项目成功制备出长度3~5 cm、直径2~3 cm 的Ca3(BO3)2、Nd:Ca3(BO3)2和Yb:Ca3(BO3)2晶体，其结晶质量达到光学级。Ca3(BO3)2晶体的热学性质优秀，在室温25ºC时热导率达到3.8 W/(m•ºC)。Ca3(BO3)2晶体自发拉曼光谱显示最强拉曼频移927 cm-1，位于X(YY)X 配置中，线宽为6.1 cm-1。在泵浦波长为266 nm (5 ns)、355 nm (25 ps)、532 nm (30 ps)和1064 nm (40 ps)的条件下，Ca3(BO3)2晶体拉曼增益测试值分别为29.6 cm/GW、16.2 cm/GW、7.7 cm/GW和2.0 cm/GW，抗激光损伤阈值分别为1.3 GW/cm2、6.5 GW/cm2、17.8 GW/cm2和49.3 GW/cm2，并观测到15条斯托克斯谱线和22条反斯托克斯谱线，实现了深紫外（266 nm）到近红外（1757 nm）多个波长的拉曼变频。本项目制备优质大尺寸Ca3(BO3)2晶体，研究了拉曼增益和晶体结构的对应关系，设计其大能量拉曼变频应用方案，胜任在200~2400 nm波段区间内多个波长的大能量拉曼激光器。