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

• Applicant: Professor Dr. Thomas Graf
• Subject Area: Synthesis and Properties of Functional Materials ; Glass, Ceramics and Derived Composites
• Term: from 2019 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 410806665

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.

• DFG Programme: Research Grants
• International Connection: China
• Partner Organisation: National Natural Science Foundation of China
• Co-Investigator: Dr. Marwan Abdou Ahmed
• Cooperation Partner: Dr. Xiaodong Xu