神光Ⅱ大型固体高功率激光装置是我国激光驱动器发展历史的里程碑, 其成功研制使我国高功率固体激光工程与技术、聚变物理与基础物理研究实现了全面且本质的跨越式发展。简要概述了神光Ⅱ激光装置研制中创新发展的大量工程方案与技术手段, 举例介绍了神光Ⅱ激光装置在近20年来的高质量运行中取得的众多有国际影响力的研究成果。经多方支持和多年持续发展, 已经形成数万焦耳级纳秒激光装置、皮秒拍瓦以及飞秒拍瓦激光装置等, 这些装置是我国惯性约束核聚变、强场物理、高能量密度物理等研究领域中重要的物理实验核心平台之一。

To improve the stability of pumping source of optical parametric amplifier, the concept of stable area in the frequency-doubling is proposed, with the numerical simulation of the frequency doubling process. Under certain intensity of the fundamental light, less than the breakdown threshold of the frequency-doubling crystal, the valid length of the frequency-doubling crystal is prolonged with the nonlinear two-pass frequency-doubling or the tandem frequency-doubling, with which the frequency-doubling course is located in the stable area and the highly stable second harmonic output with high conversion efficiency is realized. The experiments prove the above conclusion, and in the experiment the nonlinear two-pass frequency-doubling method is used to ensure the work area of the frequency-doubling in the stable area. The fluctuation of the second harmonic is less than ±2% for the 1064 nm fundamental Gaussian pulse with flutuation ±5.7%, and the conversion efficiency exceeds 70% for high-order Gaussian pulses. The experimental results show that the stability of the second harmonic is near 3 times higher than that of the fundamental light.

为了实现光参变放大抽运光源高稳定输出的目的。通过对倍频过程的数值模拟分析,提出倍频中存在“稳定区”的概念,在基频光强一定的条件下(小于倍频晶体破坏阈值),通过非共线双程倍频的方式或串联倍频的方式可有效延长倍频晶体的有效作用长度,保证倍频工作区能够被控制在“稳定区”内,从而实现高稳定高转换效率的倍频输出。实验数据验证了这一结论,实验中,利用非共线双程倍频的方式使得倍频工作区在“稳定区”内,对波动±5.7%的1064 nm高斯脉冲基频光, 倍频光波动小于±2%,脉冲形状为高阶高斯脉冲,转换效率大于70％,实验结果表明,倍频光的稳定性指标相对于基频光提高了近3倍。

A LDA pumped highly stable Nd∶YLF ring laser is developed. With an output laser intensity induced negative feedback control of resonator gain, a quasi-continuous prelase with duration of ～100 μs is established, then Q-switch during this prelase. Because the prelase mode is well matched to the resonator eigenmode and with certain intensity, the build up time and intensity of Q-switched pulse are very stable. Experimental results show that intensity instability of output Q-switched pulse doesn′t exceed 4.3%, and time jitter does not exceed ±4 ns.

For inertial confine fusion experiment, temporary pulse shaping technique is of great significance. With the development of the ICF technology,the demand of the temporary fill rate of terminal pulse is higher and higher. To satisfy the requirement of ICF experiment,by using own-designed “knife edge” apparatus and improved temporary-space transform pulse shaping technique,the pulse shaping on “Shenguang-Ⅱ” facility is realized. In the terminator,the square laser pulse with pulse width 1.16 ns,rise time 337 ps, fall time 360 ps, temporary filling factor 81.2%, is obtained. This pulse totally satisfies the requirements of the physical experiment. At the same time, some improvement is put forward to satisfy the higher experimental requirements in the future.

A novel method is presented for compensating deflection in temporal-spatial transform pulse shaping system, using single-mode optical fiber instead of a second electrooptic deflector. By changing the width of filtering slit, pulse duration ranging from 740 ps to 4.5 ns is observed, and output beam is of good quality. This novel method has reduced requirements on electrooptic deflector and simplified the whole system.

对惯性约束聚变实验而言,激光时间脉冲整形具有非常重要的意义.随着惯性约束聚变技术的不断发展,对终端脉冲的时间填充因子的要求越来越高,直接导致了对前端系统时间脉冲整形技术的要求也越来越高.为了满足惯性约束聚变实验对前端时间脉冲整形技术的要求,自行设计了"刀口器"装置.利用这一装置,并结合改进的时空变换脉冲整形技术,在"神光-Ⅱ"的升级装置上,实现了大功率激光装置上的激光时间脉冲整形,在终端得到了脉宽1.16 ns、上升沿337 ps、下降沿360 ps、时间填充因子为81.2%的方波激光脉冲, 满足了物理实验对前端系统激光时间脉冲整形的要求.同时,提出了进一步改进的措施,以满足今后物理实验的更高要求.

提出了时空变换脉冲整形系统中光束复原的一种新方法:用单模光纤代替通常时空变换法中的第二个电光偏转器.当改变调制狭缝的宽度时,获得了脉宽在740 ps～4.5 ns连续变化的整形脉冲,而且输出光束质量好.此方法降低了对关键元件电光偏转器的要求,提高了可靠性,简化了系统.

成功研制了一台激光二极管列阵(LDA)抽运的高稳定Nd:YLF环形激光器.用输出激光强度负反馈控制谐振腔的增益,建立了准连续的～100 μs宽预激光状态,然后在此预激光基础上调Q.由于预激光模式与谐振腔固有模式一致并且具有一定强度,调Q脉冲的建立时间和幅度都很稳定.实验结果为:输出调Q脉冲强度起伏不超过4.3%,时间抖动小于±4 ns.

新型LD泵浦振荡器采用环形结构,具有单纵模几率高、时间波形和幅度高度稳定等特点,这些特点使其与多程放大器的联机非常方便,没有系统多脉冲注入破坏风险和能量不稳破坏风险.联机实验取得了显著成果,输出能量达1.252kJ,是当前国内固体激光器单束输出最高能量,此时输出脉冲脉宽为1.26ns,光束口径为20cm×20cm,平均功率密度达2.5GW/cm².