高功率光纤飞秒激光器用高阶色散补偿镜的研究

In recent years,femtosecond fiber lasers have attracted much attention as practical alternatives to solid-state lasers,owing to its reliability,compactness and stability.Affected by the nonlinear effect,mainly self-phase modulation(SPM)，the primary limitation to achieving shorter pulses was attributed to uncompensated third-order dispersion(TOD). In this proposal,we present a new TOD compensation technology using multilayer mirrors.The design of TOD mirrors will be theoretical studied with phase optimiztion based on floating constants. Thickness error sensitivity will be considered in the merit function to obtain robust design.A wide-band optical monitoring system in both reflection and transmission will be developed in Dual Ion Beam Sputtering(DIBS) plant.Various methods to determine the critical point during the deposition will be developed to obatin better thickness accuracy. On-line reverse engineering and re-optimization will be utlized to improve the production yield of TOD mirror.A Michelson white-light interferometer in both time and frequency domain will be built up.An algorithm to extract TOD from the measured interferogram will be provided. The effect of spectral resolution and stability of nanomter stepper on the measurement accuracy will be analyzed.As the above issues involving both science and technology are solved,dispersive mirrors with high order dispersion will be developed to satisfy the requirement of high power femtosecond fiber lasers.

具有可靠性、简约性和稳定性的光纤飞秒激光是新一代超快激光技术。受到自相位调制等非线性效应的影响，在高功率光纤飞秒激光中高阶色散补偿成为限制超短脉冲输出的最主要因素。本项目提出了光学多层薄膜实现高阶色散补偿的新方案。理论上研究TOD补偿镜的设计方法，采用带浮点相位优化，并通过把容差加入评价函数，提高设计结果的鲁棒性。基于双离子束溅射，实验上深入研究透反射光学宽波段监控提高厚度精度的方法，探索不同的判停方式、在线快速反演、再优化对制备良率的提高。搭建时-频域白光干涉系统，研究波长-时间-能量三维数据提取TOD的算法，分析光谱分辨率、纳米步进平台重复性对测试精度的影响。随着这些科学和技术问题的解决，将实现高阶色散补偿元件的研制，满足高功率光纤飞秒激光技术的需要。

项目执行过程中，在设计上，以多个共轭腔为初始结构，采用粒子群(PSO)优化算法优化GDD，分别设计了针对Ti:Sapphire和Yb:YAG两种固态飞秒激光用的宽波段啁啾镜和高色散反射镜，相比常规的变尺度等方法，PSO的搜索收敛速度明显提高；考虑到1nm的厚度容差，比较了不同设计的鲁棒性。搭建了时/频域白光干涉系统测试多层薄膜的相位特性，发展波长/时间/能量三维数据提取群延迟的算法；研究了包络线法、平滑算法对TOD精度的影响，提高了测试的稳定性和精度。采用自制的双离子束溅射设备，基于晶振/时间的复合监控策略，针对钛宝石飞秒激光系统，设计和制备了600nm-1000nm内反射率>99.5%，提供平均-40fs2 GDD补偿量的啁啾镜对，实验测试结果和设计相吻合，两个啁啾镜的GDD震荡实现了互补，在系统应用中成功实现了锁模，获得了29fs的脉冲输出，这也是国内第一个实验制备的宽波段啁啾镜对。针对大模场掺Yb光子晶体光纤飞秒激光系统，设计和制备了GDD补偿量-1500fs2的高色散补偿镜，经腔外压缩获得了270fs的脉冲输出。在国际上首次提出了多层介质薄膜的差分相移分束镜，并在实验上进行了验证，已在中国工程物理院偏振测试仪上的到应用。