Two localized CO₂ laser treatment methods for mitigation of UV damage growth in fused silica

Two methods:high-power,short-time,single-shot irradiation(Method A) and low-power,long-time,multi-shot irradiation(Method B) are investigated to mitigate the UV damage growth in fused silica by using a 10.6-μm CO2 laser.To verify the mitigation effect of the two methods,the laser induced damage thresholds(LIDTs) of the mitigated sites are tested with a 355-nm,6.4-ns Nd:YAG laser,and the light modulation of the mitigation sites are tested with a 351-nm continuous Nd:YLF laser.The mitigated damaged sites treated with the two methods have almost the same LIDTs,which can recover to the level of pristine material.Compared with Method A,Method B produces mitigated sites with low crater depth and weak light modulation.In addition,there is no raised rim or re-deposited debris formed around the crater edge for Method B.Theoretical calculation is utilized to evaluate the central temperature of the CO2 laser beam irradiated zone and the radius of the crater.It is indicated that the calculated results are consistent with the experimental results.     

裂纹或气泡对熔石英损伤修复坑场调制的近场模拟

建立了含有裂纹或气泡的高斯型修复坑的3维模型, 用3维时域有限差分方法研究了熔石英后表面该类缺陷对355 nm入射激光的近场调制. 研究表明, 裂纹的调制明显大于气泡或者高斯坑本身, 因此为了抑制修复元件的初始损伤, 应尽量避免任何未修复的裂纹存在, 尤其是与入射光呈夹角约25°的裂纹, 同时应避免尺寸大于5 λ 的气泡存在. 当裂纹或气泡位于近表面层3 λ 以内且靠近修复坑环边缘时, 对场的调制最明显. 随着侧移的增加, 近表面区缺陷诱导场叠加, 强点总数涨落较大且易形成极大峰值, 特别是含有裂纹的情形; 远表面区强点总数逐渐增大并趋于稳定. 随着嵌深的增加, 强点的数目大体呈减弱趋势, 当嵌深大于3 λ 时, 逐渐趋于平缓振荡. 如果裂纹或气泡位于坑点正下方几个波长内, 激光辐照下其效果相当于延长了高斯坑的深度.     

CO2激光扫描辐照修复熔石英表面损伤

采用振镜系统结合10.6 m的CO2激光,对熔石英表面损伤点进行辐照,成功地修复了直径500 m的大尺寸损伤点,损伤修复后表面无烧蚀残留,损伤内部完全愈合,无气泡和残余裂纹。和定点修复方式相比,这种修复具有修复尺度大、面形影响区域小、应力分布范围小的优势。80%扫描辐照修复的损伤点的初始损伤阈值恢复甚至超过了基底的初始损伤阈值。     

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

Theoretical studies show that the Hertzian-conical crack can be considered to be composed of double cone faces for simplification. 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 the 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 filled with remainder polishing powders or water vapor/drops. Meanwhile, the laser-induced initial damage is moving 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.     

激光装置片状放大器组件的氙灯可靠性分析

 整理惯性约束聚变激光装置的运行记录和氙灯的故障数据,得到10种氙灯故障现象,并且归纳为3类,即触发故障、绝缘故障和氙灯爆炸,按故障发生时间可以分为“引发失效”的故障和“舍生取义”的故障。分析3类氙灯故障与片状放大器组件以及装置打靶成功率的逻辑关系,生成基于氙灯故障的装置打靶故障树,描述氙灯可靠性对于装置打靶成功的重要性。分析氙灯的生产工艺流程和工艺缺陷,生成氙灯的故障与工艺的鱼刺图,揭示氙灯故障的根源。     

基于加速退化数据的金属化膜脉冲电容器可靠性分析

 基于金属化膜脉冲电容器的失效机理,研究了基于加速退化数据的金属化膜脉冲电容器可靠性评估问题,给出了一个该型电容器的加速退化失效模型和参数统计推断方法。基于试验数据可求得该型电容器可靠性模型中未知参数的估计值分别为9.066 9×10^{-8sup>和0.022 1,将该值代入失效分布函数即可确定电容器的失效模型,由此模型求得该型电容器充放电20 000次的可靠度为0.972 4。使用这种分析方式对金属化膜脉冲电容器进行可靠性分析将更能节省试验时间和费用。}     

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。     

Yb3+:YAG片状激光器的温度效应及金刚石窗口冷却设计

基于准三能级速率方程分析了Yb3+:YAG 片状激光器的温度效应,结果表明随着激光介质的温度由300 K升高到400 K,激光器的储能提取效率由43%下降到26%。提出了利用热传导性能及优异的金刚石窗口对激光片的两端面进行冷却设计。模拟结果表明对掺杂11.6 %厚度为1.2 mm的激光片在泵浦功率密度为15 kW/cm2,重复频率为10 Hz的条件下,要将最高温度控制在可接受的范围内（比如320 K）,周围冷却水的对流换热系数不应小于2 kW/(m2·K）。模拟结果还表明,在相同的热功率密度和冷却条件下,减小激光片的厚度同时增加抽运光的传输次数可以明显的降低激光片的温度。     

高平均功率开关晶体热力学特性有限元分析

基于有限元数值方法,就不同的光强分布模型以及电光晶体固定或自由的边界条件,模拟分析了KDP,DKDP,LiNbO3,BBO开关晶体材料在高平均功率激光负载下的热力学特性。结果表明:激光作用数s后,温升分布基本与光强分布一致;晶体表面的最大轴向位移和最大拉应力随光斑填充因子增大而增大;晶体的力学边界约束对最大轴向位移及最大拉热应力的影响随着光斑填充因子的增大而增强;在相同的入射激光光源及相同的边界条件下,KDP上的温升最大,热畸变最严重,DKDP次之,而LiNbO3和BBO具有较低的温升值或较低的热形变和热应力。     

高功率激光放大器片腔洁净度实验研究

 在氙灯放电泵浦过程中,放大器片腔内材料在高强度氙灯光辐照下,存在显著的热解过程,产生大量的微米级悬浮粒子。在两种实验条件下对粒子数进行了测量：一是放大器氙灯泵浦结束之后悬浮粒子的自然消散过程;二是氙灯泵浦结束之后利用大气流量的超纯氮气冲洗片腔之后的粒子数测量。研究结果表明,正常情况下,氙灯泵浦结束后片腔洁净度达到了10~50万级气溶胶的水平(在粒子直径Φ 0.5 μm的水平上)。利用大气流量的超纯N₂气冲洗片腔能够在短时间内显著地提高片腔的洁净度。