介稳腔内激光偏振可塑性实验及机理研究

Axially symmetric polarized laser beam is one of hot topics in the areas of the developed laser devices in recent years. Axially symmetric polarized beams have received considerable attention due to their unique characteristics in polarization and potential applications. An effective solution to deal with the thermal effect and cavity design in the all solid state lasers would be a pressing physical problem for obtaining the controllable polarized laser with high effective and stability. In this proposal, an effective approach for the switching of the polarization states is proposed by the using of a metastable laser resonator due to its excellent mode selectivity. The mechanism of the plasticity of polarization would be revealed in the metastable resonator. Moreover, a 4f-pumping scheme with a slab crystal would be developed for alleviating the thermal effect and polarization degradation to explore effective thermal management techniques. Since the intra-cavity multi-physics coupling effect causes the different stabilities in the tangential and sagittal planes，the specific polarization state can be achieved by the separation and extraction of TE and TM waves. The stable and switchable axially symmetric polarized laser would be generated by further refinement of some important experimental parameters including thermal controlling, pumping system and the resonator, which contributes to the development of novel solid-state laser devices.

轴对称偏振激光是现今激光器件研究的主要热点之一。其独特的偏振特性和潜在的应用价值，已经引起了研究人员的广泛关注。为了获得高效高稳定性的可控偏振光，有效地处理全固态激光器件热效应和谐振腔设计成为一个亟待解决的关键物理问题。本项目将采用介稳腔结构，借助其优异的模式选择能力探索实现偏振态之间切换的有效方法，揭示介稳腔内激光偏振可塑性机理。此外，为缓解热效应和偏振退化，采用板条结构激光晶体和4f泵浦系统，探索有效的热管理技术。由于腔内的多重物理耦合效应引起子午面和弧矢面的稳定性的差异，TE波和TM波被分离和提取获得特定的激光偏振态。改进热控制、泵浦系统和谐振腔等因素，获得稳定可控的轴对称偏振激光，为新型固态激光器件的发展作出贡献。

现今，激光器的偏振特性及其潜在的应用价值日益受到研究人员的广泛关注。在全固态激光器件中，合理有效地解决热效应问题和谐振腔设计成为获得高效高稳定性的可控偏振激光的重要环节。本项目设计高效受激拉曼转化的Z型谐振腔结构和侧面泵浦结构，在声光调制下获得线偏振Nd:YAG/YVO4激光。实验结果表明YVO4晶体的非对称受激拉曼增益是获得均一激光线偏振态的机理，给出高效稳定线偏振激光的一种获得途径。经过YVO4的受激拉曼效应可获得稳定的线偏振拉曼激光，其偏振比约为10.4dB。这是由于YVO4晶体属四方晶系，其拉曼效应在//C和⊥C的两个方向产生了各向异性，线偏振方向则平行于c轴。获得最大的一阶斯托克斯1175nm激光输出功率为1.8W。另一方面，为缓解热效应和偏振退化，采用块状和板条结构Yb:YAG激光晶体，探索有效的热管理和双波长激光输出技术。基于Yb:YAG双波长激光振荡阈值的理论,实验研究获得了连续双波长激光输出。实验中，采用10%、15%和20%的输出耦合镜，分别实现了单波长和双波长激光输出，在最高泵浦功率为20W时，输出耦合率分别为10%、20%，最高获得3.94W的1050nm激光和3.40W的1030nm激光，对应的光光转换效率分别为19.7%和17.0%；当输出耦合率为15%、泵浦功率为11.7W时，获得0.79W的双波长激光，对应的光光转换效率为6.8%。当1030nm激光功率为3.0W时，30min内输出功率RMS稳定性优于1%。全固态的线偏振激光及双波长激光在激光通信、高精度传感、非线性光学频率变换、光束合成等领域有重要的应用价值。