新型铥掺杂氧化镥钪陶瓷光谱展宽效应及2μm波段超快激光特性研究

Laser sources delivering ultrashort pulses in the 2 μm spectral region are becoming a research focus in the field of ultrafast all-solid-state laser technology. Due to the advantage of high thermal conductivity and distinctive spectroscopic characteristics, novel Tm:(LuxSc1-x)2O3 ceramic is a promising laser material for achieving high power ultrafast lasers in the 2 μm spectral region. This project will systematically study the spectral lines broadening effect of the novel ceramic and evaluate the performance of high power ultrafast Tm:(LuxSc1-x)2O3 ceramic laser in the 2 μm spectral region. The main research contents include: understanding the influence of Tm3+ doping concentration and ratio of Sc/Lu on the thermal conductivity of ceramic; indicating the dependence of the emission linewidth, stimulated emission cross-section and lifetime of upper laser level on the ratio of Sc/Lu, and finding the key parameters for balancing the thermal conductivity and spectral lines broadening in Tm:(LuxSc1-x)2O3 ceramic; exploring the influence of the characteristics of laser ceramic and saturable absorber on the average output power and pulse width, realizing the mode-locking operation of LD pumped Tm:(LuxSc1-x)2O3 ceramic laser by use of SESAM or graphene, and generating the femtosecond laser pulses in the 2 μm spectral region with average output power exceeding 1W. It is hoped that the efficient laser materials and technique for supporting high average power ultrashort pulses generation in the 2 μm spectral region can be obtained by the implementation of this project.

2μm波段超快激光是近年来全固态超快激光技术的研究热点之一。新型铥掺杂氧化镥钪陶瓷同时具备高的热导率和独特的光谱特性，是获得高平均功率2μm超快激光的有潜力的激光介质。本项目将系统研究该新型陶瓷的光谱展宽效应，评价其在2μm波段高平均功率超快激光的运转特性，具体内容包括：明确铥离子掺杂浓度、镥钪比对陶瓷热导率的影响规律；揭示荧光增益线宽、受激发射截面、激光上能级寿命等随镥钪比的变化趋势，找到平衡该型激光陶瓷热导率与光谱展宽效应的关键参数；探究激光陶瓷特性、饱和吸收体参数与超快激光输出功率、脉冲宽度等的内在关系，基于SESAM、石墨烯等成熟的锁模元件，实现LD泵浦陶瓷激光器连续波锁模运转, 获得平均输出功率>1W的2μm波段飞秒激光输出。希望通过本项目的实施，能够为高平均功率2μm波段超快激光产生提供有效的材料和技术支撑。

课题组围绕2μm固体激光产生、调制及优化相关的基础问题，基于研究团队在新型倍半氧化物激光陶瓷制备方面的进展，紧密跟踪国际上激光技术研究的热点，在高功率Tm掺杂陶瓷激光器性能表征与新现象探索、新型氧化物陶瓷激光性能表征及基于新型饱和吸收体的短脉冲激光产生及调制等方面开展了研究工作，取得了系列研究成果：基于泵浦光场、激光场和热场之间相互耦合的物理过程，建立了3D热模型及改进的速率方程组理论模型，在2μm掺Tm固体激光器运转方式、功率（能量）提升、波长调谐及双稳态运转等方面开展了研究工作，获得了100 W连续激光及20.7 mJ (1 kHz，84 ns)调Q激光输出，实现了基于VBG的宽范围、窄带宽的调谐激光运转，首次报道了近衍射极限的掺铥Innoslab 激光器及热透镜效应驱动的2 μm波段陶瓷激光双稳态运转。在新型激光陶瓷性能表征与新现象探索工作方面，提出了“Cooperatively Enhanced Reabsorption”固体激光器自脉冲运转方案，研究了Er掺杂氧化物陶瓷自脉冲运转特性，获得了最短脉冲宽度185 ns的2.7 μm 脉冲输出；在Tm:Y2O3陶瓷中获得了7.25 W连续激光及最小脉冲宽度为115 ns的调Q激光输出，中心波长在2050 nm左右；在Er:Y2O3陶瓷中获得了2.05 W 2.7 μm连续激光输出。在金纳米棒饱和吸收体的制备、短脉冲激光产生及调制方面，制备了平均长径比为7.3的金纳米棒，并首次在固体激光器中实现了基于纳米金饱和吸收体的被动调Q激光运转，获得了最大单脉冲能量19 μJ 1064 nm激光脉冲输出；利用纳米金饱和吸收体具备饱和吸收带宽大且可调控的特点，通过提高金纳米棒的长径比，首次在2 μm 波段激光器中实现了纳秒量级调Q脉冲运转，最大单脉冲能量为4.94 μJ，相应的脉冲宽度和重复频率分别为896 ns 和77 kHz。