掺铥倍半氧化物陶瓷协同跃迁调控机理及2.3μm波段激光特性研究

High-power and multiple-operation-state laser sources in the 2.3 µm spectral can find many promising applications in the detection of important trace gas, laser noninvasive detection and basic scientific research. 2.3 µm (3H4→3H5) laser generation from the directly LD-pumped Tm-doped solid-state materials is a promising technique. However, limited by the laser materials and laser transition losses, the research progress on the 2.3 µm Tm-doped lasers is relatively slow, and the corresponding several hundreds of milliwatts output power is far less than the transition in the common 2 µm spectral of Tm-doped lasers (3F4→3H6). The project proposes a research plan for realizing high efficient generation of 2.3 µm laser in Tm-doped sesquioxide ceramics based on the regulation mechanism of collaborative transition. Tm-doped sesquioxide ceramics with low phonon energy and high thermal conductivity will be chosen as the gain medium.The 2 µm laser transition of 3F4→3H6 in Tm3+ will be collaboratively used to open up new channels for population transfer, realizing the effective population of 3H4 level. This project aims to carry out the research on the fabrication and characterization of Tm-doped sesquioxide ceramics, modelling and regulating the mechanisms of collaborative laser transition, realization of high power continuous-wave (CW) laser operation, and Q-switching and mode-locking operation of 2.3 µm Tm-doped sesquioxide ceramic laser. CW output power larger than 5W, 100ns-level Q-switched pulses and ps mode-locked pulses are expected to be achieved, respectively. It is expected that the implementation of this project can provide new effective methods and laser materials for the high power 2.3 µm Tm-doped solid-state lasers.

高功率、多运转状态的2.3μm波段激光在重要痕量气体探测、激光无创检测及基础科学研究方面有重要的应用前景。利用LD泵浦掺铥固体介质产生2.3μm（3H4→3H5）激光是有潜力的技术方案。但受制于激光介质及跃迁损耗等，掺铥2.3μm波段激光研究进展相对缓慢，数百毫瓦级输出功率远落后于其常规的2μm波段（3F4→3H6）。本项目提出基于协同跃迁效应实现掺铥倍半氧化物陶瓷2.3μm激光高效产生的方案，以低声子能量、高热导率倍半氧化物陶瓷作为激光介质，利用Tm3+自身2μm跃迁开辟粒子数转移的新通道，实现3H4能级粒子数的有效布局。项目旨在通过激光陶瓷制备与表征、协同跃迁机制建模与调控、高功率连续激光运转、调Q与锁模脉冲运转等研究的开展，实现高功率连续激光（>5W）、100-ns级调Q及ps锁模脉冲激光运转。希望通过本项目的实施，能够为高功率2.3μm波段固体激光提供有效的技术和材料支撑。

项目团队围绕提升与拓展2.3 µm掺铥固体激光器运转性能的目标，从泵浦方案、跃迁调控、激光材料及脉冲产生等方面开展了系统性研究工作。采用785 nm LD直接泵浦方案，在掺铥晶体中实现了瓦级连续功率输出及输出波长的有效拓展，表明利用LD直接抽运Tm单掺固体介质产生高功率2.3 μm波段激光是重要的技术途径之一。进一步利用Cr:ZnSe、ReSe2、金纳米棒等饱和吸收体，实现了2.3 μm掺铥固体激光器的被动调Q运转。在跃迁机制调控方面，在Tm3+单掺固体激光介质中实现了基于协同跃迁的1.9μm（3F4-3H6）和2.3μm (3H4-3H5) 波段的双波长激光运转。利用三镜腔研究了由一个共输入镜和两个独立的输出耦合器构成的双波长激光器运转性能，实现了785 nm LD泵浦Tm:YLF 1.9和2.3 μm的双波长激光同步振荡。在连续运转状态下，1908 nm的连续输出功率为5.49 W，2305 nm的连续输出功率为1.12 W，总的光-光转换效率为43.5%。相对于2.3μm单波长激光运转的传统方案，协同跃迁机制下2.3μm激光输出功率提升了14.3%。进一步使用Cr:ZnSe实现了被动调Q双波长激光运转。针对3F4能级的粒子数捕获效应，进一步提出了GSA和ESA双波长泵浦2.3 μm掺铥激光器的方案，为该波段掺铥激光器实现更高输出功率提供了一种有效技术手段。将785 nm（GSA）、1470 nm（ESA）双波长泵浦方案应用于Tm:YLF晶体，实现了1.8 W 2.3 μm连续激光输出，相对于0.8 μm单波长泵浦，输出功率提升了60%。对于Tm:YAP晶体，双波长泵浦下2.3μm激光的最大输出功率达2.28 W，相比单波长泵浦方案功率提升了65.2%。进一步利用Tm:YAP晶体3H4→3H5跃迁各向异性的宽带发射光谱特性，采用特殊镀膜的输出镜及双波长泵浦方案，实现了1.62 W 2446 nm激光输出，丰富了掺铥固体激光器的输出波长，相关工作入选《中国激光》杂志先进中红外激光技术及应用特别专题。研究团队基于新型级联非线性变频等方案，开发了786 nm、1.7 μm等波段纳秒量级脉冲激光器。根据掺铥激光材料的吸收特性，以上波段的激光器可以用于泵浦掺铥固体介质，进一步实现增益开关型脉冲激光产生，从而拓展2.3 μm掺铥固体激光器运转模式。