基于GSA-ESA双波长抽运Er:Lu2O3晶体3μm激光特性研究

Bing the starting range of middle infrared band, 3 μm lasers, are the limitting wavelength which can be efficiently attained by solid state lasers. Their field of applications is manifold: in medicine, in gas-sensing systems, as well as for pumping optical parametric oscillators. Erbium is the most interesting active ion in 3 μm lasers, however due to the prety high quantum defect efficiency (~65% to ~73% under 790 nm (4I15/2→4I9/2) or 974 nm (4I15/2→4I11/2))and the shortage of laser diod pump sources with long wavelength emission, the efficiency of 3 μm lasers is far wawy from near infrared lasers. In Erbium active ion, the laser levels system is quite complex, the long lifetime of the lower laser level (4I13/2) induces high population density of this level during laser operation and thus increases the laser threshold and terminates the laser transition. An efficiente solution to this prolem is to decrease the population deposition on lower laser level (4I13/2), which can be easyly realized by using exite state absorption (ESA) pumping cooperating with ground state absorption，named "GSA-ESA daul-wavelength linkage pumping scheme" in this propose. Conventional excitation of laser media raises individual atoms or ions directly to energy levels above the emitting level. However, as we show here, energy states lying well above those populated by incident light can be reached by re-pumping cooperative excite state absorption processes at rates sufficient to sustain stable, steady-state population inversions. Employing Er:Lu2O3 crystals as the host material, spectroscopy will be investigated to provide the hint of dule-wavelength pump scheme. The lower laser level will be depopulated, the pump energy will be recycled and the multi-photon relaxation process will be weaken, in the end, efficient 3 μm laser opeartion with low threshold and high efficiency which relieve the bottleneck of the quantum defect limit can be expected. Dule-wavelength pump scheme will demonstrates a new way to realize efficient 3 μm laser operation.

中红外3μm波段处于水分子强吸收带内，在激光医疗、遥感探测、光参量放大等领域有广泛的应用前景。Er3+是产生3μm激光的主要激活离子，但其下能级（4I13/2）寿命较长（~12 ms），易导致激光再吸收甚至猝灭，激光量子亏损较高（~65%），传统的抽运方式难以获得高效率激光输出。为此，本项目以低声子能量、高热导率的Er:Lu2O3晶体为研究对象，构建GSA-ESA双波长抽运理论模型，分析Er3+能级跃迁动力学过程及其对激光输出特性的影响。利用Er3+离子下能级寿命较长的特点，结合激发态吸收机理，通过双波长抽运技术，实验研究3μm激光连续运转特性。通过本项目的实施，有效减少Er:Lu2O3晶体3μm激光下能级粒子数，弱化多声子弛豫所产生的冗余热影响，实现低阈值、高效率激光输出，为进一步实现高功率中红外激光运转提供理论基础和技术指导。

本项目利用Er3+离子下能级寿命较长的特点，结合激发态吸收机理，通过双波长抽运技术，有效减少Er:Lu2O3晶体3μm激光下能级粒子数，弱化多声子弛豫所产生的冗余热影响，实现低阈值、高效率激光输出，为进一步实现高功率中红外激光运转提供理论基础和技术指导。本项目所获结果如下：.1）首次在常温下实现10.7 W的高功率Er:Lu2O3晶体3 μm激光输出。.2）首次将WS2作为饱和吸收体被运用在1645 nm 的Er:YAG激光器中，并实现了稳定的激光运转。在吸收泵浦为6.24 W，透过率为10%的情况下，获得了最好的实验结果：0.42 W的输出功率，1.8 μs 脉冲宽度，25.13 kHz的重复频率，相应的单脉冲能量为16.75 μJ。.3）首次将MoS2作为可饱和吸收体用于3 μm波段的激光调制。将其成功运用于平均功率超过1 W的Er:Lu2O3激光器，所获得的335 ns脉宽，也是迄今为止在3 μm波段，所有使用二维材料作为调Q元件所实现的最短脉冲宽度。.4）将BP作为可饱和吸收体，实现了755 mW的2.84 μm的调Q激光输出，所获得的359 ns脉冲宽度，是迄今为止所有在3 μm波段使用BP作为可保和吸收体获得的最窄脉冲宽度。我们的实验结果也证明了BP在3 μm波段锁模方向的巨大潜力。.5）首次将g-C3N4作为可饱和吸收体用于3 μm波段的激光调制。我们作为首批发现其可饱和吸收特性的课题组，自行完成合成、剥离及可保和吸收体的制备，并将其用于Er:Lu2O3激光的调制。获得的1.09 W平均输出功率及351 ns脉冲宽度，在使用二维材料作为可保和吸收体对3 μm波段激光进行的调Q实验中，是最好的结果之一，证明该材料在可保和吸收激光调制领域有着极大的应用价值。