Utilizing polarization maintaining photonic crystal fiber (PM-PCF) with the low temperature coefficient of birefringence, a two-dimensional tunable and temperature-insensitive Lyot filter aiming to compensate the frequency modulation to amplitude modulation (FM-to-AM) conversion in high power laser facility is demonstrated. The Jones matrix is applied to analyze the relationship between optical characteristics of the filter and physical parameters (including amplitude ratio, phase delay, and susceptibility of the birefringence to temperature) of the polarization optical field. Both the transmission peak wavelength and extinction ratio of the spectral transmission are able to be changed simultaneously, hence, it shows more efficient FM-to-AM compensation ability. Besides, the transmission peak shift is about 18 pm/℃ with the PM-PCF configuration, which is about two orders of magnitude less than the normal polarization maintaining fiber (PMF) configuration. The demonstrated filter presents a practical application potential in large scale laser driven facility.

高功率超短脉冲激光器在强场物理、精密加工及**应用等各种领域均有广泛的应用前景。随着半导体泵浦源和光纤制造工艺的进步，超短脉冲光纤激光器的输出功率得到了极大提升，且由于光纤具有散热性好、环境稳定性好、光束质量好等优势，高功率超短脉冲光纤激光器及其放大压缩技术在近几年得到了越来越多研究人员的关注。聚焦于目前高功率超短脉冲光纤激光器及其放大压缩技术的前沿研究，综述了目前产生高功率、高能量超短光纤脉冲种子源的几种新方法（如Mamyshev锁模、“9字腔”锁模和时空锁模），并介绍了相干合束和脉冲非线性压缩技术在光纤中产生高功率超短脉冲的最新进展。

The SG-Ⅲ laser facility (SG-Ⅲ) is the largest laser driver for inertial confinement fusion (ICF) researches in China, which has 48 beamlines and can deliver 180 kJ ultraviolet laser energy in 3 ns. In order to meet the requirements of precise physics experiments, some new functionalities need to be added to SG-Ⅲ and some intrinsic laser performances need upgrade. So at the end of SG-Ⅲ's engineering construction, the 2-year laser performance upgrade project started. This paper will introduce the newly added functionalities and the latest laser performance of SG-Ⅲ. With these function extensions and performance upgrade, SG-Ⅲ is now fully prepared for precise ICF experiments and solidly paves the way towards fusion ignition.

利用全矢量有限元法分析了光子晶体光纤(PCF)的结构参量对其本征模场分布的影响。数值计算结果表明, 具有多层空气孔、多层纤芯、大孔间距和大占空比的结构更有利于将光场约束在纤芯中, 纤芯层数、孔间距和占空比的增加均会导致PCF本征模场出现更高阶次的模式。纤芯层数和孔间距的增加会对由占空比减小所引起的功率泄漏进行一定的补偿, 通过减小空气占空比、增加纤芯层数和孔间距, 可实现大模场单模传输的可行性。对于4层空气孔、2层纤芯、占空比为0.01、孔间距为20 μm的PCF, 在保证单模传输的条件下, 纤芯半径可达40 μm, 有效模面积为3717 μm2, 纤芯功率集中度为68.32%。

惯性约束聚变精密物理实验要求高功率激光驱动器具备时域-频域精密调控能力, 以实现对激光与等离子体相互作用过程中非线性效应的抑制。基于保偏光纤和单偏振光纤技术, 采用温度调谐双振荡器结合两级波导相位调制器实现激光脉冲频域精密调控, 采用两级高速电光调制脉冲整形技术实现激光脉冲时域精密调控, 将微波射频信号取样检测与声光开关进行连锁以确保整个系统的安全运行。实验获得了光谱带宽为0.15～0.3 nm、中心波长范围为1052.4～1053.6 nm的连续可调微焦耳级激光脉冲, 波长调谐精度为0.1 nm,在微焦级实现了对比度大于500∶1的高对比度整形激光脉冲, 脉冲时间波形顶部调制深度小于10%。

采用相位调制技术产生的具有一定光谱分布的相位调制脉冲可以有效抑制高功率激光驱动器中大口径光学元件的横向受激布里渊散射和满足光束匀滑需求, 但该脉冲在装置各系统传输放大过程中, 由于光谱畸变会引起幅频调制(FM-to-AM)效应, 这种效应严重影响了激光装置的输出性能及实验效果。介绍了相位调制脉冲产生原理、引起FM-to-AM效应的根本原因及因素, 综述了目前美国的国家点火装置、法国的兆焦耳装置以及我国的神光-Ⅲ主机装置在FM-to-AM效应抑制技术方面取得的重要进展。

研究了一种用于惯性约束聚变激光驱动器的纳秒级、高精度整形激光脉冲产生技术。采用中心波长为980 nm的激光二极管作为参考光, 以自动调控幅度调制器的偏置工作点, 实现了脉冲工作体制的幅度调制。基于高速电光调制技术, 采用两级幅度调制器设计了主振荡功率放大型全光纤激光脉冲产生装置。其中, 第1级幅度调制器用于对输入连续运转的单纵模激光进行初始精密脉冲整形, 第2级幅度调制器用于对激光脉冲进行二次精密整形和时域噪声抑制。实验研究表明, 该激光脉冲产生装置可输出脉冲宽度在“0.1~50.0 ns”范围内连续可调、对比度大于20001的高精度任意整形激光脉冲, 满足了激光脉冲产生装置较强脉冲控制能力的要求。