由于3 µm激光跃迁能级的特殊性，传统抽运方式必然导致较低的量子效率，其激光输出指标相比于近红外波段严重滞后。在此研究背景下，本项目基于3 µm激活离子下能级寿命长、距离基态较远的特点，提出“双波长级联输出”的技术途径，通过2 µm激光的输出，消耗激光下能级堆积粒子数，促进3 µm激光的产生。旨在有效缩短粒子在激光下能级停留的时间，同时减少无辐射跃迁产生的热量，并以氟化物晶体这种具有低声子能量和负折射率温度系数等优点的基质为研究对象，研究和发展高效率、低阈值的3 µm激光新技术。主要内容包括：明确掺钬级联激光的动力学过程，建立正确的理论模型；采用级联激光技术，实验研究Ho:LiLuF4激光晶体中红外激光性能，实现高质量的3 µm激光输出，突破目前3 µm固体激光器的技术瓶颈，探索实现高转换效率的中红外固体激光技术新途径，为实现中红外激光的高功率输出奠定技术基础。

Owing to the particularity of transition levels of 3-μm lasers, the traditional pump method inevitably leads to lower quantum efficiency. Compared with the near-infrared wavelength, the output recordes of 3-μm lasers have severely lagged behind. In view of the problem of long lifetime and large gap to the ground state of the lower laser level for 3-μm active ions, we will put forward the technique of "dual-wavelength cascade laser" to realize efficient, lower threshold 3-μm lasers in this project, which can depopulate the lower laser level effectively by generating the 2-μm laser, and reduce the heat caused by multi-phonon relaxation. The fluoride crystal which has the merits of lower phonon energy and negative temperatural coefficient of refractive index will be investigated. According to the laser dynamic process of the cascade laser, we will establish its appropriate theoretical model. After that, the mid-infrared characteristics of the Ho:LiLuF4 crystal will be researched to obtain high conversion efficiency 3-μm laser. The holmium-doped fluoride crystal cascade laser technique will solve the technique bottleneck of 3-μm solid state lasers, and explore a new route to realize high conversion efficiency for mid-infrared solid state lasers, which will lay a technical foundation to high power mid-infrared lasers.