基于侧边泵浦Tm:YVO4晶体键合Ho:YVO4晶体板条结构的线偏振Ho激光器研究

Ho lasers play an important role in fields such as environmental monitoring, medical treatment, and photo-electronic countermeasure, which are also the important pump sources for 3~12 μm mid-infrared non-linear frequency conversion. For the urgent requirements of Ho lasers in expense-saving, facilitation, and miniaturization, this project proposes a novel linear polarized Ho laser mechanism, which could be edge-pumped by normal 800 nm LD arrays in a single slab geometry consisting of Ho:YVO4 and Tm:YVO4 crystals. With the large absorption cross section of the Tm:YVO4 part at 800 nm, high-power Tm laser can be generated via the cross-relaxation between Tm ions and confined intra-slab efficiently, where the 1.9 μm wavelength is well-matching the absorption band of the Ho:YVO4 part. Hence, efficient linear polarized Ho laser could be generated owning to the birefringence nature of YVO4 crystal. Robustness of the Tm/Ho composite laser has been verified by the applicant previously. With the excellent thermal control ability of the slab geometry, beginning with the measurement of spectral parameters of each part of the Tm/Ho:YVO4 slab, the applicant prepare to carry out both theoretical and experimental researches about manipulating wavelength-drift of the Tm-doped part, evaluating laser properties of the slab laser, and analyzing the thermal effects and laser stabilities. With the above researches, this project tries to provide an effective route for a compact normal-LD-pumped linear-polarized Ho laser at room temperature.

Ho激光器在环境监测、医疗、光电对抗等领域有重要应用价值，是3~12μm中远红外非线性频率变换的重要泵浦源。针对Ho激光器研究在经济便捷、可小型化等方面的迫切需求，本课题拟发展一种新型Ho激光实现方式，直接采用800nmLD侧边泵浦，通过将Tm:YVO4与Ho:YVO4晶体键合成板条结构，实现线偏振Ho激光的高效率输出。其中，Tm:YVO4部分具有大泵浦吸收截面，能通过交叉弛豫产生禁锢于板条内部的1.9μm激光，并匹配Ho:YVO4部分的共振吸收带，进而可利用晶体的双折射特性，高效地实现线偏振Ho激光输出。申请人已对Tm/Ho键合激光器进行了实验论证，借助板条结构的高热管理能力，拟从各键合部分的光谱参数入手，掌握板条内部Tm激光的波长操控规律，对Tm/Ho:YVO4板条激光器的功率放大能力、热效应及稳定性等进行研究，探索出一条可实现常规LD泵浦、小型化、线偏振室温Ho激光输出的有效路径。

2.1μm激光位于重要中远红外晶体ZGP和OP:GaAs等的截止吸收带，是实现高性能中红外激光的理想驱动源。因此，也制约整个中红外激光系统的体积，造价和效率。相对于现有的1.9μm激光同带泵浦2.1μmHo激光器。本项目另辟蹊径，首创提出基于掺Tm和掺Ho增益介质集成来实现常规半导体激光器直接泵浦的高效率Ho激光输出，无需额外的1.9μm激光系统，实现了2.1μm激光光源的小型化，进而有利于降低中红外激光系统造价，实现装备的小型化，以应用到国防领域的光电对抗，气体探测，激光通信与测距等。以Tm/Ho:YVO4板条激光器为切入点，围绕着新型Tm/Ho键合激光技术，开展系统性研究。构建并完善Tm/Ho键合增益介质的速率方程计算模型和热效应计算模型，评估Tm/Ho键合结构存的输出功率制约因素和热管理问题，并探索出若干热效应缓解策略；设计出Tm/Ho:YVO4和Tm/Ho:YLF键合增益介质，并从上述晶体中分别获得3.62 W的线偏振Ho:YVO4和10.2 W的线偏振Ho:YLF激光输出，论证了Tm/Ho键合腔内泵浦Ho激光机制在钒酸盐和氟化物等增益结构上实现高效率，小型化2.1 μm Ho激光输出的可行性，达到项目既定的激光输出功率指标，在Optics Letters， Optics Express，和Optics and Laser Technology等重要光学杂志上累计发表SCI论文14篇（高于既定2~4篇SCI论文的预期成果），申请发明专利5项（1项获得授权），协助培养博士研究生 3 名，硕士研究学生 1 名（已获学位）。