可有效实现 2μm超短脉冲激光输出的掺铥稀土碱金属氟化物单晶体研究

The 2μm mid-infrared femtosecond laser has important applications in the field of civil and military. Traditional 2μm femtosecond laser has shortcomings of large volume, low conversion efficiency, expensiveness and poor stability of system due to its generating from the frequency upconversion of ultrafast light source of Ti:sapphire. In ordr to overcome the technical difficulties in the current lack of 2μm femtosecond laser materials with good properties, the project aims to investigate a thulium doped rare earth alkali metal fluoride single crystal with high quality for 2μm ultrashort pulse laser. We intend to study the growth parameters of Tm3+ doped LiYF4、LiLuF4、NaYF4 et al.fluoride single crystals with Bridgman method. Thulium doped fluoride single crystals with high 2μm emission cross section, wide emission band and long fluorescence lifetime will be obtained by investigating the effect of crystal component, parameter of crystal field and thiulum doping concentration on 2μm emission properties and energy transfer mechanism. The laser rod of Tm3+ doped crystal will be processed from the obtained crystal. The laser performance of the rod will be deeply analyzed. The final purpose of the this research is to achieve the 2μm femtosecond fiber laser output. It is proposed that the Tm3+ ion doped single crystals possess comprehensive performance in thermal stability, chemical-physical property, mechanical strength, optcal transmission, and 2μm emission, and the performance of high-proficiency 2μm ultrafast laser output will be realized. Finally, this project will provide a new choice for 2μm femtosecond crystal laser materials in the future.

中红外2μm飞秒激光在民用及军事领域具有重要应用。传统的2μm 飞秒激光是基于钛宝石超快光源经频率上转换后产生，具有体积大、转换效率低、及系统稳定性差等缺点。针对目前缺乏性能优良的2μm飞秒激光材料这一技术瓶颈问题，本项目拟开展一种可有效实现2μm超短脉冲激光输出的掺铥优质大尺寸稀土碱金属氟化物单晶研究。研究Tm3+掺杂LiYF4、LiLuF4、NaYF4等晶体的坩锅下降法生长工艺。通过晶体组分、晶格场参数、Tm3+掺杂浓度对2μm发光特性与机理的研究，获得具有2μm发射截面高、发光带宽、荧光寿命长的掺铥晶体。以此晶体为材料，加工成激光棒。通过对棒的激光输出特性深入研究，最终实现2μm波段飞秒脉冲激光输出。Tm3+掺杂稀土碱金属氟化物单晶体可望具备热学、物化、光学透过及2μm发光等综合性能优良的特性，有望获得有效2μm飞秒激光输出。本项目研究结果将为2μm飞秒激光晶体提供新的增益基质选择。

中红外2.0 μm飞秒激光在民用及军事领域具有重要应用。本项目开展了可有效实现2.0 μm 激光与超短脉冲激光输出的掺铥优质大尺寸稀土碱金属氟化物单晶研究。研究了Tm3+掺杂优质LiYF4、LiLuF4、α-NaYF4 、Na5Lu9F32单晶体的坩锅下降法关键制备生长工艺。通过晶体组分、晶格场参数、Tm3+掺杂浓度对2.0 μm发光特性与机理的研究，获得了具有2.0 μm发射截面高、发光带宽、荧光寿命长的掺铥晶体。以Tm3+掺杂的LiYF4与LiLuF4为基础加工成尺寸为3×3×5 mm3体块晶体，采用976 nm半导体激光器作为泵浦源，利用短平-平腔进行激光测试。采用Tm: LiYF4最高获得了1.8 W激光输出，相应的光光转换效率和斜效率分别为51%和57%；采用Tm:LiLuF4最高获得了0.8 W激光输出，相应的光光转换效率和斜效率分别为34%和26%。采用Tm: LiYF4晶体,选用5镜折叠腔，利用半导体可饱和吸收镜（SESAM）作为可饱和吸收体，通过优化腔型结构和腔内光斑/光强分布，最终实现了中心波长1.88 μm连续波锁模激光运转，输出功率为200 mW，重复频率为63.5 MHz，脉冲宽度约为~20 ps。进一步优化腔型结构，补偿腔内色散，可获得~100 fs的激光输出。本项目研究结果为2 .0 μm飞秒激光晶体提供新的增益基质选择。

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