Research for high-power femtosecond Yb^<3+>:Y_2O_3 ceramic laser

基于在陶瓷YAG激光器开发过程中积累的知识和技术，我们开始研究一种具有进一步激光潜力的新材料Y_2O_3 （ytria）。Yb^<3+>:Y_2O_3是一种新型激光材料，比YAG具有更高的导热性、更宽的带宽和更短的脉冲产生。但其熔点高达2430℃，给晶体生长带来了困难。采用纳米晶技术制备激光陶瓷的新方法，在1700℃的烧结温度下制备了Y_2O_3陶瓷，该温度低于2280℃的相变温度，成功获得了高质量的大尺寸激光材料。我们用激光二极管（LD）端泵浦证明了Yb:Y_2O_3具有高达9.2 w功率和72%效率的连续振荡，从而证明了其作为激光材料的优异性能。利用半导体饱和吸收镜成功地实现了无源锁模，产生了平均功率高达420兆瓦的430-fs脉冲。我们还成功地通过砷化镓饱和吸收器锁定模式，并启用了ld直接泵浦飞秒固态激光器。在激光发展的道路上，我们研究了YAG和Y_2O_3的光谱、热和力学性能。实验证明，多晶陶瓷激光材料的热冲击参数比单晶高3倍以上，适用于高密度泵浦和高功率激光器。陶瓷激光器的尺寸可扩展性和强断裂韧性对聚变驱动器具有重要意义，因为它们的工作极限是由增益材料的热冲击参数决定的。我们还开发了复合陶瓷。发现掺杂离子的扩散距离比传统扩散键的扩散距离长5倍以上，陶瓷键合的机械强度与块状陶瓷一样高。两者都表明复合陶瓷结合良好。对其它倍半氧化物Sc_2O_3和Lu_2O_3等新材料的研究也已开始。这些掺镱材料具有像Yb:Y_2O_3一样宽的发射光谱。发现Yb:Lu_2O_3在掺杂条件下仍具有较高的热导率，有望成为高平均功率飞秒激光器。少

Based on knowledge and technologies accumulated in the development of ceramic YAG laser, we started investigation of a new material Y_2O_3 (yttria) with further potentials for lasers. Yb^<3+>:Y_2O_3 is a new laser material enabling higher thermal conductivity, broader bandwidth, and shorter pulse generation than YAG. However, its high melting temperature of 2430℃ has made difficulty on crystal growth. By applying our novel fabrication method of laser ceramics based on nanocrystalline technology, Y_2O_3 ceramic was fabricated at a sintering temperature of 1700℃, which is lower than the phase-transition temperature of 2280℃ and then high-quality laser material was successfully obtained with a large size. We have demonstrated CW laser oscillation of Yb:Y_2O_3 with as high as a 9.2-W power and 72% efficiency by laser-diode (LD) end-pumping and thus given evidence of its excellent property as a laser material. Passive mode-locking by semiconductor saturable-absorber mirrors was successfully … More demonstrated and transform-limited, 430-fs pulses with as high as a 420-mW average power were generated. We also succeeded in mode-locking by a GaAs saturable-absorber and enabled LD-direct pumped femtosecond solid-state laser. On the way of laser developments, we have investigated spectroscopic, thermal, and mechanical properties of YAG and Y_2O_3. It was then experimentally proved that a polycrystalline ceramic laser material has a more than three times higher thermal shock parameter than a single crystal, which is suitable for high-dense pumping and high-power lasers. The characteristic size scalability and strong fracture toughness of ceramic lasers are of significance for fusion drivers because their operation limits are determined by thermal shock parameters of the gain materials. We also developed composite ceramics. It was found that the diffusion distances of doped ions are more than fiver times longer than those by conventional diffusion bonding, and the mechanical strength of the ceramic bonding is as high as that in a bulk ceramic. Both indicate the perfect bonding of composite ceramics. Investigation of new materials such as other sesquioxides Sc_2O_3 and Lu_2O_3 have also started. These Yb-doped materials have broad emission spectra like Yb:Y_2O_3. It was found that Yb:Lu_2O_3 will be promising for high average power femtosecond laser because of the higher thermal conductivity even under doping. Less