正交线偏振小间隔双波长准连续和连续固体拉曼激光器的研究

Dual-wavelength solid-state lasers with a small wavelength separation are of great interest because of their important applications such as spectroscopy, differential lidar and terahertz-wave difference-frequency generation. Compared with fundamental lasers, Raman lasers have the advantages of beam quality improvement, pulse duration shortening, and purer spectrum. Orthogonally linearly polarized dual-wavelength lasers with a small wavelength separation can be separated easily and are desirable for phase matching of the THz generation. In this project, a wavelength-locked laser diode (LD) is introduced as the in-band pumping source in a dual-wavelength solid-state Raman laser with a small wavelength separation. First, we will reduce thermal effects and improve pump absorption by using double-end polarized pumping and optimizing polarization direction of the pump laser. Based on this, two orthogonally linearly polarized emission lines with comparable stimulated emission cross section are employed to generate dual-wavelength fundamental laser, and a crystal which has two orthogonally polarized Raman lines with similar Raman frequency shifts and gain is used as Raman medium. Then the balance between dual-wavelength Raman lasers can be adjusted through the choice of crystals, as well as optimal design of resonant cavity structure and coating. As a result, reliable and high-efficiency orthogonally linearly polarized dual-wavelength quasi-cw and cw Raman lasers with a small wavelength separation will be obtained, which would be extremely valuable laser sources for the generation of terahertz waves and differential lidar.

小间隔双波长激光在光谱学、差分吸收激光雷达和差频产生太赫兹波等方面有着重要应用。相比于基频双波长激光，拉曼激光具有光束质量好、脉宽窄、光谱纯度高等独特优势。正交线偏振的小间隔双波长拉曼激光器不仅易于分光，且在差频产生THz波时更有利于满足相位匹配条件。因此，本项目在小间隔双波长拉曼激光器中，采用波长锁定LD作为共振泵浦源，首先通过优化泵浦光偏振方向和采用双端泵浦方式来改善晶体热效应、提高泵浦吸收率。在此基础上，选择发射截面相近的、偏振方向垂直的、波长间隔较小的两个波长作为基频光，选择垂直偏振泵浦时拉曼频移波数和增益都较相近的晶体作为拉曼介质，通过晶体的选择、谐振腔结构和腔镜膜系优化，平衡双波长激光的振荡，最终实现正交线偏振的1.1x um和1.5x um波段小间隔双波长准连续和连续拉曼激光的高效稳定输出。该研究在差频产生太赫兹波及差分吸收激光雷达等领域有着重要应用，具有十分重要的研究意义。

正交偏振双波长激光在精密测量、太赫兹产生、差分雷达、光谱分析等领域有着重要的应用前景。相比于基频双波长激光，拉曼激光具有光束质量好、脉宽窄、光谱纯度高等独特优势。在本项目的资助下，课题组围绕产生正交偏振双波长拉曼激光输出，开展了1.1 um和1.5 um波段正交偏振双波长准连续和多波长连续波固体拉曼激光器的研究，取得了如下阶段性科研成果：.（1）采用共振泵浦技术改善热效应，分别以YVO4和BaWO4晶体作为拉曼频移介质，获得了1.1 um波段连续波拉曼激光的高功率输出，研究了晶体性能和谐振腔结构对激光器输出性能的影响。.（2）直接采用复合Nd:YVO4晶体作为自拉曼频移介质，继续在采用共振泵浦技术改善热效应的基础上，通过优化晶体长度和谐振腔结构来提高泵浦吸收率和拉曼转换效率，实现了1.1 um波段正交偏振多波长连续波拉曼激光的同时输出。.（3）以复合Nd:YVO4晶体作为激光介质，高增益的BaWO4晶体作为拉曼频移介质，在采用共振泵浦技术和增大泵浦光斑改善热效应的基础上，实现了Nd:YVO4/BaWO4内腔分体式拉曼激光器一阶和二阶Stokes多波长连续波拉曼激光的同时输出，并对不同激光谱线之间的增益竞争机制进行了理论和实验研究。.（4）以复合Nd:YVO4晶体作为自拉曼频移介质，综合使用共振泵浦、放大泵浦光斑、复合晶体三种技术途径来减轻热效应，通过优化晶体长度和谐振腔结构来提高基频激光增益和拉曼激光转换效率，成功实现了1.5 um人眼安全波段连续波拉曼激光的高效输出。.（5）以Nd:YLF晶体作为激光介质，BaWO4晶体作为拉曼频移介质，采用耦合腔结构，通过优化晶体长度、谐振腔结构和不同偏振泵浦来平衡双波长拉曼激光的振荡，获得了功率相近的正交偏振1.1 um波段双波长拉曼激光输出。. 通过本项目的实施，了解和掌握了不同泵浦方式、不同晶体规格性能、不同谐振腔结构对固体拉曼激光器输出性能的影响，揭示了固体拉曼激光器的设计规律，发现了共振泵浦、复合晶体和放大泵浦光斑等有效改善热效应的途径，并探讨了不同激光谱线之间的增益竞争机制，为正交偏振双波长固体拉曼激光器的研究和设计提供了详细技术资料。