Fabrication of sesquioxide (Yb:Lu2O3 and Yb:LuScO3) laser materials and their applications in high power ultrafast Thin-disk lasERs (“LuThER”)

薄板激光器（TDL）是一种非常有前途的激光结构，可以产生高平均功率和高能量的脉冲。由于激光介质中的晶体长度短，光束直径大，因此可以在最小化有害的非线性和热效应的同时进行功率缩放。这一关键优势尤其适用于产生峰值功率高的皮秒和飞秒脉冲。到目前为止，由于大多数关于功率缩放的研究都集中在增益材料Yb:YAG上，大功率锁模振荡器的TDL概念的全部潜力尚未得到开发。由于其有限的增益带宽，Yb:YAG并不是最适合产生飞秒脉冲的激光晶体。相比之下，掺镱倍半氧化物Yb:Lu2O3和Yb:LuScO3单晶或透明陶瓷由于其宽增益带宽、低量子缺陷、强晶体场效应、优异的热机械性能和低声子能量，是产生高能量和高平均功率的超短脉冲的非常有前途的激光介质。因此，本项目的目的是研究实现大面积（直径>12mm）高质量Yb:Lu2O3和Yb:LuScO3晶体和陶瓷的不同关键技术及其在大功率TDL中的应用。因此，拟议的项目将包括以下调查：将分析和克服目前热交换生长方法和边缘定义薄膜喂养生长技术在可生产晶体的尺寸和质量方面的局限性。为了开发和生产具有显著提高激光性能的晶体，将研究其成分、局部晶体结构和光谱特性之间的关系。为了获得高纯度、高烧结活性和避免团聚，将进一步研究湿化学合成纳米晶粉末的方法。采用真空烧结技术对Yb:Lu2O3和Yb:LuScO3粉末进行烧结，制备出高光学质量的陶瓷。对制备的目标直径超过12 mm的陶瓷的光学质量进行验证，并研究其在薄板激光器中的应用和性能。在理论考虑的支持下，我们将详细阐述适合超快薄盘激光器的倍半氧化物激光晶体和陶瓷的系统优化指南。高平均功率的锁模薄盘激光器进行系统分析，并将生产的大直径倍半氧化物陶瓷与倍半氧化物晶体的性能进行比较。一个被动模型锁定振荡器将与市售sesam一起实现，用于研究和鉴定平均功率超过150 W、脉冲持续时间低于500 fs的增益材料。

The thin-disk laser (TDL) is a highly promising laser architecture to generate pulses at high aver-age powers and high energies. Due to the short crystal length and large beam diameters in the laser medium, power scaling is possible while minimizing the detrimental nonlinear and thermal effects. This key advantage holds, especially for the generation of picosecond and femtosecond pulses with high peak powers. So far the full potential of the TDL concept for high-power mode-locked oscillators was not yet exploited as most of the investigations on power scaling were fo-cused on the gain material Yb:YAG. Due to its limited gain bandwidth Yb:YAG is not the most suitable laser crystal for the generation of femtosecond pulses. In contrast, the Yb-doped sesqui-oxides Yb:Lu2O3 and Yb:LuScO3 either as single crystals or as transparent ceramics are very promising laser media for the generation of ultrashort pulses with high energies and at high aver-age powers thanks to their broad gain bandwidth, low quantum defect, strong crystal field effects, excellent thermo-mechanical properties and low phonon energies. Therefore the aim of the present project is the investigation of the different key technologies for the realization of large-area (diameter>12mm) high-quality Yb:Lu2O3 and Yb:LuScO3 crystals and ceramics and their application in high-power TDL. The proposed project therefore will include the following investigations: The current limitations of the heat-exchange growth method and the edge-defined film-fed growth technique concerning size and quality of the producible crystals will be analyzed and overcome. The relation between the constituents, the local crystal structure, and the spectral properties will be investigated in order to develop and produce crystals with significantly improved laser perfor-mance.The wet chemistry synthesis of nano-crystalline powders will be further investigated to obtain high purity, high sintering activity and avoid agglomeration. The Yb:Lu2O3 and Yb:LuScO3 powders will be sintered by the vacuum sintering technology to produce ceramics with high optical quality. Up-on validation of the optical quality of the prepared ceramics with targeted diameters exceeding 12 mm, their application and performance in thin-disk lasers will be investigated.The developed sesquioxide crystals and ceramics will be implemented in cw anSupported by theoretical considerations we will elaborate a guideline for the systematic optimiza-tion of sesquioxide laser crystals and ceramics that are suited for ultrafast thin-disk lasersd mode-locked thin-disk lasers with high average powers to perform a systematic analysis and compare the per-formances of the produces sesquioxides ceramics (with large diameters) to that of the sesquiox-ide crystals. A passively modelocked oscillator will be implemented with commercially available SESAMs to investigate and qualify the gain materials at average powers beyond 150 W and at pulse duration below 500 fs.