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

基于陶瓷激光器研制过程中积累的知识和技术，我们开展了一种极具发展潜力的新型材料Y_2O_3(Y_2O_3)的研究工作。Yb^&lt；3+&gt；：Y_2O_3是一种新型激光材料，具有比激光晶体更高的导热系数、更宽的带宽和更短的脉冲输出时间。但其熔化温度高达2430℃，给晶体生长带来了困难。采用基于纳米晶技术的激光陶瓷制备新方法，在低于2280℃相变温度的1700℃的烧结温度下制备了Y2O_3陶瓷，成功地获得了高质量的大尺寸激光材料。利用激光二极管(LD)端面泵浦的方法，实现了Yb：Y_2O_3的连续激光振荡，输出功率高达9.2W，激光效率达72%，证明了Yb：Y_2O_3是一种优良的激光材料。利用半导体可饱和吸收镜实现了被动锁模的…产生了平均功率高达420 mW的430fS脉冲，显示了更多和变换受限的脉冲。利用可饱和吸收腔实现了锁模，实现了LD直接泵浦的飞秒固体激光器。在激光发展的道路上，我们研究了YAG和Y_2O_3的光谱、热学和力学性能。实验证明，多晶陶瓷激光材料具有比单晶高三倍以上的热冲击参数，适用于高密度泵浦和高功率激光器。陶瓷激光器特有的尺寸可扩展性和较强的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震参数决定的。我们还开发了复合陶瓷。结果表明，掺杂离子的扩散距离比传统扩散连接的扩散距离长5倍以上，且机械强度与块体陶瓷相当。两者都表明复合陶瓷的完美结合。对其他倍半氧化物Sc_2O_3和Lu_2O_3等新材料的研究也已开始。这些掺Yb的材料具有像Yb：Y_2O_3一样的宽发射光谱。研究发现，即使在掺Yb的情况下，Yb：Lu_2O_3仍具有较高的热导率，因此有望成为高平均功率飞秒激光器。较少

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