设计了一种高功率的固体皮秒脉冲激光放大器。采用增益介质为Nd∶YAG材料的传导冷却端面泵浦板条放大器结构设计,通过板条结构多角度放大,实现对皮秒脉冲激光的四程放大。分析板条端面切角与激光入射角度的选取对填充因子以及激光功率放大的影响。最终实现了在种子光重复频率为100 kHz、激光脉冲宽度为9.6 ps的工作条件下,系统输出激光功率为103 W,单脉冲能量为1.03 mJ。

A new laser amplifier structure based on Ndglass regenerative amplifier and off-axis four-pass amplifier is designed for high power laser facilities. The parasitic oscillation and pencil beam of the four pass amplifier are studied and a method is introduced to suppress them. By injecting a 1053 nm single longitudinal mode laser pulse with pulse duration of 3 ns and pulse energy of 1 nJ, a 10.3 J amplified pulse with a 2% shot-to-shot energy stability is obtained. The total gain of the amplifier system is over 1010. The output laser beam is a flat top profile with a 71% near field fill factor and modulation of 1.4 and 91% pulse energy can be focused into 2 times of diffraction limits. The experimental results and output performance of the amplifier system fully meet the requirements of the pre-amplifier of high power laser facilities, which shows that multi-pass amplifier can be used in high power laser facilities.

The prompt pump-induced wavefront characteristic of high power laser facility is undertaken to address an important aspect of the wavefront control system for the high power laser facility. Based on the ShenGuang Ⅱ four-pass amplification high power laser facility (SG-Ⅱ-FAF), numerical simulation is conducted on the prompt pump-induced wavefront distortion through ANSYS and Matlab. In order to obtain the space-time characteristics and variation features, the Hartmann wavefront analyzer is employed to conduct experiments on prompt pump-induced wavefront distortion and thermal wavefront recovery aberration after xenon lamp pumping. The numerical simulation results agree well with experimental results. The prompt pump-induced wavefront distortion of single-slab-amplifier is about 0.12λ (wavelength λ=1053 nm) of peak-to-valley (PV), and the whole optical wavefront of the SG-Ⅱ-FAF is about 5λ of PV with different laser beams, whose shape looks like a “saddle”. Simulations and experiments provide important data for the wavefront control system of SG-Ⅱ-FAF, emission laser passing through the space filters sucessfully and pumping uniformity of slab Ndglass amplifier. As a result, the far-field focus spot energy concentration of the laser beam is improved, meanwhile the success rate and the working efficiency of the SG-Ⅱ-FAF operational experiment are increased.

提出了一种新型的高功率激光装置的预放系统结构，采用钕玻璃再生放大结合离轴四程放大的技术途径，研究了四程放大中寄生振荡和笔形光束的产生机理和抑制措施。通过注入脉宽为3 ns，单脉冲能量小于1 nJ的1053 nm单纵模种子激光，可以获得10.3 J的近衍射极限输出，总增益大于1010，能量稳定性为2%，输出激光为近平顶分布，近场填充因子为71%，近场调制度约为1.4，91%的焦斑能量能聚焦于2倍衍射极限内。实验结果和输出性能完全满足激光装置预放系统的性能要求，验证了多程放大技术在高功率激光装置预放系统中应用的可行性。

高功率激光驱动器动态波前特征及其规律是激光驱动器光束波前质量控制关键研究内容之一。以神光Ⅱ四程放大高功率激光驱动器为研究平台，使用ANSYS和Matlab对激光驱动器瞬时动态波前进行了模拟计算，并利用哈特曼波前分析仪对驱动器氙灯抽运引入的瞬时动态像差和热恢复像差进行了实验研究，得到其时空特性和变化规律。理论模拟和实验结果具有一致性，单片片状放大器动态像差峰谷(PV)值约为0.12λ (波长λ=1053 nm)，驱动器总体瞬时动态像差PV值约为5λ ，呈“瓦片”形态。模拟计算和实验分析为神光Ⅱ四程放大高功率激光驱动器光束波前质量控制、激光发射顺利通过空间滤波器和片状放大器抽运均匀性优化等提供了重要的参考数据，提升了输出光束远场焦斑能量集中度，提高了驱动器激光发射的成功率和运行效率。

基于小信号增益公式、菲涅耳反射公式和判断内腔四程放大高功率激光系统寄生腔增益与损耗大小,研究了2个光路构型相似,寄生腔构成相近的高功率固体激光装置(装置A和装置B)的系统寄生振荡问题:首先指出了系统中存在可能起振的3个寄生腔,然后分析了3个寄生腔中影响损耗的各个因素,根据装置A上的实验结果,判断在仅通过钕玻璃片检偏的情况下,装置B的第3寄生腔存在产生寄生振荡的可能性,最后采取加入一组偏振片的方法抑制寄生振荡。

Beam automatic alibnment system is used to implement beam adjustment .Basing on the principle of matrix optic，the mathematical model for auto-alignment in four-pass amplifier is built by analyzing the properties of this system. Using this model, the shems of beam alignment is designed and the analytical solutions of the amounts of near field adjustment and far field adjustment are obtained, respectively.

根据在大型高功率固体激光装置中自适应光学技术的应用研究,将变形镜置于腔镜位置,有利于提高自适应光学系统的校正动态范围.基于变口径90°翻转四程放大系统的光路特点,从理论上比较完整地解决了四程放大系统腔镜位置变形镜面形解的存在性问题,并对口径变换比值(缩束比)与面形求解之间的关系问题进行了数值模拟,结果表明:只要缩束比小于1,对应系统连续波前畸变的腔镜位置面形解是存在的,且随着缩束比减小,解的收敛性增强.

以"四程+助推"放大系统为例,运用蒙特卡罗(Monte-Carlo)法计算分析了放大过程中注入能量、放大增益及损耗单独存在随机变化和以上因素共同作用时对系统输出能量稳定性的影响.计算结果表明,系统输出能量稳定性对四程小信号增益系数和腔内光学元件透过率的随机变化相当敏感;小信号增益随机变化明显大于注入能量对输出能量稳定性的影响.同时,也说明应用蒙特卡罗方法解决随机性问题的有效性和简洁性.

根据原型装置主放大系统组合式四程放大结构的特点,计算分析了放大过程中注入能量、放大增益及损耗的微小起伏对系统输出能量稳定性的影响.根据原型装置集成实验结果,分析了目前原型装置单路输出能量稳定性水平.研究结果表明:注入能量越大,其变化对输出能量影响越小;小信号增益系数对输出能量的影响明显大于注入能量;系统输出能量稳定性对腔内光学元件的透过率变化要求高于腔外光学元件.在3 ns基频光输出达标点处要使输出能量不稳定性控制在5%以内,注入能量起伏要低于10%,腔内放大片小信号增益系数起伏要低于1%,腔内光学系统损耗起伏要低于2%.