熔石英亚表面修复形貌对光场的调制

基于标量衍射理论, 计算了熔石英亚表面高斯型修复形貌对于光场的调制，用Matlab对结果进行了仿真并与实验结果进行了比较。所得结果表明，二者有较好的一致性, 一定尺度的高斯面型修复形貌会对光场产生调制，且调制度随光场传输位置变化，通过适当选择后续光学元件位置，可降低光场调制造成光学元件损伤的风险。     

Mitigation of laser damage growth in fused silica by using a non-evaporative technique

A non-evaporative technique is used to mitigate damage sites with lateral sizes in a range from 50 μm to 400 μm and depths smaller than 100 μm.The influence of the pulse frequency of a CO 2 laser on the mitigation effect is studied.It is found that a more symmetrical and smooth mitigation crater can be obtained by increasing the laser pulse frequency form 0.1 to 20 kHz.Furthermore,the sizes of laser-affected and distorted zones decrease with the increase of the laser pulse frequency,leading to less degradation of the wave-front quality of the conditioned sample.The energy density of the CO 2 laser beam is introduced for selecting the mitigation parameters.The damage sites can be successfully mitigated by increasing the energy density in a ramped way.Finally,the laser-induced damage threshold(LIDT) of the mitigated site is tested using 355 nm laser beam with a small spot(0.23 mm 2) and a large spot(3.14 mm 2),separately.It is shown that the non-evaporative mitigation technique is a successful method to stop damage re-initiation since the average LIDTs of mitigated sites tested with small or large laser spots are higher than that of pristine material.     

High Efficient C6H12 Raman Laser Enhanced by DCM Fluorescence

We report the first-order Stokes output （wavelength of 627.6 nm） from C6H12 enhanced by DCM dye fluorescence with high energy conversion efficiency of 47.9%, quantum conversion efficiency of 56.5%. To our knowledge, it is the highest conversion efficiency of stimulated Raman scattering obtained from liquid Raman laser. A 532nm frequency doubled Nd：YAG laser with 8 Hz repetition rate is employed as the pump source, and the enhancement medium is DCM dye solution in ethanol. The conversion efficiencies at various pump energies and various pump repetition rates are measured and analysed. The enhancement mechanism of SRS together with its potential application is discussed.     

组合式片状放大器热恢复模拟研究

 针对组合式片状放大器工作时的热量沉积特性,分析了氙灯箱和片腔的冷却过程,重点研究了激光介质钕玻璃片的热恢复过程。初步的热分析表明,为每支氙灯提供4.7×10^-3m³/s的冷却气量以及为每个片腔提供7.6×10^-3m³/s的冷却气量时能够满足装置4小时一发的运行频率要求。     

片状放大器热恢复研究

 给出了神光III主放大器单元4×2×3片状放大器的热恢复研究。利用集总热容模型研究了氙灯、隔板玻璃、钕玻璃片的热恢复过程,并利用三维瞬态热传输有限元模型对钕玻璃片的三维空间温度随时间的变化过程作了详细的分析。初步的研究结果表明,通过优化的冷却方案,可以在装置预定的运行周期内将激光工作介质钕玻璃片内的温度梯度和总体平均温度冷却到可以接受的水平。     

光参量啁啾脉冲放大系统非线性晶体长度确定及调谐方法研究

首先介绍了模拟光参量啁啾脉冲放大（OPCPA）过程的多种计算模型,在此基础上提出了三步走逐步逼近算法,以确定OPCPA过程中最稳输出时所需的非线性晶体长度.这种算法综合利用了上述计算模型,随着计算模型越来越精确,非线性晶体长度的计算范围越来越小.因而利用这种算法能高效、精确地确定最佳非线性晶体长度.最后提出在OPCPA过程引入一定的相位失配量,来调谐最稳输出时所需晶体长度,从而能突破晶体加工精度不够的局限,在实际OPCPA过程中获得稳定输出.     

熔石英表面损伤修复点的损伤概率

针对3个光斑尺寸的CO2激光辐照尺寸小于400 m损伤点后得到的修复点,从4个方面对损伤修复点经355 nm激光辐照后的损伤概率分别进行研究。结果表明,根据修复光斑尺寸或损伤点尺寸分别讨论修复点的损伤概率,更能反映修复点的抗激光损伤能力。通过分别讨论可以看出,采用小光斑CO2激光辐照损伤点或者修复尺寸小于200 m的损伤点,修复成功率超过90%。同时,可以通过损伤修复点的激光损伤阈值都服从正态分布的规律来预测修复点的损伤概率。     

激光钝化对熔石英修复后损伤性能影响的实验研究

采用10.6 μupm 的 CO₂激光, 对单次激光脉冲辐照修复熔石英存在的烧蚀采用大光斑钝化去除. 经过辐照修复的区域置于前表面测试初始损伤阈值, 结果表明调制造成的损伤得到了一定程度的抑制; 辐照区域置于后表面修复后 熔石英的初始损伤阈值超过了基底的初始损伤阈值. 实验观察到了应力分布外扩, 同时明显减弱. 对损伤增长的测试说明, 经过激光熔融辐照后的损伤点, 当应力释放以后, 损伤扩展初期表现出指数增长趋势, 后期随着辐照次数的增加, 损伤增长不再明显, 并且趋于恒定值.     

Incident laser modulation of a repaired damage site with a rim in fused silica rear subsurface

Local CO2 laser treatment has proved to be an effective method to prevent the 351-nm laser-induced damage sites in a fused silica surface from exponentially growing, which is responsible for limiting the lifetime of optics in high fluence laser systems. However, the CO2 laser induced ablation crater is often surrounded by a raised rim at the edge, which can also result in the intensification of transmitted ultraviolet light that may damage the downstream optics. In this work, the three-dimensional finite-difference time-domain method is developed to simulate the distribution of electrical field intensity in the vicinity of the CO2 laser mitigated damage site located in the exit subsurface of fused silica. The simulated results show that the repaired damage sites with raised rims cause more notable modulation to the incident laser than those without rims. Specifically, we present a theoretical model of using dimpled patterning to control the rim structure around the edge of repaired damage sites to avoid damage to downstream optics. The calculated results accord well with previous experimental results and the underlying physical mechanism is analysed in detail.     

Rear-surface light intensification caused by a Hertzian-conical crack in 355-nm silica optics

Theoretical studies show that a Hertzian-conical crack can be considered to be composed of double cone faces for simplicity. In the present study, the three-dimensional finite-difference time-domain method is employed to quantify the electric-field distribution within the subsurface in the presence of such a defect under normal incidence irradiation. Both impurities (inside the crack) and the chemical etching have been investigated. The results show that the maximum electric field amplitude |E| max is 9.57374 V/m when the relative dielectric constant of transparent impurity equals 8.5. And the near-field modulation will be improved if the crack is filled with the remainder polishing powders or water vapor/drops. Meanwhile, the laser-induced initial damage moves to the glass-air surface. In the etched section, the magnitude of intensification is strongly dependent on the inclination angle θ. There will be a highest modulation when θ is around π/6, and the maximum value of |E| max is 18.57314 V/m. When θ ranges from π/8 to π/4, the light intensity enhancement factor can easily be larger than 100, and the modulation follows a decreasing trend. On the other hand, the modulation curves become smooth when θ > π/4 or θ < π/8.