表面Al膜污染物诱导熔石英表面损伤特性

在熔石英表面人工溅射一层Al膜污染物,分别测试污染前后熔石英基片在355 nm波长激光辐照下的损伤阈值,并采用透射式光热透镜技术、椭偏仪和光学显微镜研究了污染物Al膜的热吸收、厚度以及激光辐照前后熔石英的损伤形貌。用355 nm波长的脉冲激光分别辐照位于污染的熔石英和洁净的熔石英前后表面的损伤点,并用显微镜在线采集损伤增长图样,测试损伤点面积。实验表明:熔石英前表面的金属Al膜污染物导致基片损伤阈值的下降约30%,后表面的污染物导致基片下降约15%,位于熔石英样片后表面损伤点面积随激光辐照次数呈指数增长,而位于前表面的损伤点面积与激光脉冲辐照次数呈线性增长关系;带有污染的熔石英样片的增长因子比洁净的熔石英样片的增长因子高30%。     

355 nm激光作用下熔石英损伤增长

 用355 nm脉冲激光分别辐照位于熔石英前后表面的损伤点,用Mias软件采集了损伤增长的图像并测量了每脉冲辐照后损伤点的面积。实验结果表明：位于熔石英样片后表面的损伤点面积随激光辐照脉冲数呈指数增长关系,而位于前表面的损伤点面积与激光辐照脉冲次数呈线性增长关系。     

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.     

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.     

355 nm皮秒激光辐照下熔石英的损伤特性

利用光学元件激光损伤测试平台,测试了355 nm皮秒激光辐照下熔石英光学元件的初始损伤及损伤增长情况,并通过荧光检测分析了损伤区缺陷。研究结果表明:皮秒激光较高的峰值功率导致熔石英损伤阈值较低,前表面损伤阈值为3.98 J/cm2,后表面损伤阈值为2.91 J/cm2;前后表面损伤形貌存在较大差异,后表面比前表面损伤程度轻且伴随体内丝状损伤;随脉冲数的增加后表面损伤直径增长缓慢,损伤深度呈线性增长;皮秒激光的动态自聚焦和自散焦导致熔石英体内损伤存在细丝和炸裂点重复的现象;与纳秒激光损伤相比,损伤区缺陷发生明显改变。     

抑制损伤发展的CO_2激光修复技术及机理研究

熔石英表面激光损伤发展问题一直制约着激光器的运行通量。采用CO2激光在线熔融修复损伤点,修复后形成一个光滑的高斯坑,去除了损伤点中的裂纹,平滑了凹凸不平的表面,并且在紫外脉冲激光作用下,修复斑再次产生损伤的阈值高于熔石英元件的损伤生长阈值。因此CO2熔融修复技术能有效地抑制损伤发展。通过分析CO2激光作用下熔石英表面的温度分布,讨论修复坑的形成过程,确定激光参数对修复效果的影响,为寻找最佳修复参数提供理论基础。同时利用原子力显微镜(AFM)、轮廓仪细致分析损伤点和修复斑的微细结构,采用有限差分时域方法计算损伤点和修复斑周围的光强分布,探索消除裂纹和平滑表面对抑制损伤生长的作用。     

熔石英表面铜颗粒污染激光诱导损伤

利用SAGA-S激光器输出的355 nm波长激光,研究了熔石英表面铜颗粒污染的激光损伤规律。采用磁控溅射的方式在洁净熔石英表面制备不同尺寸的颗粒状污染物,用1-on-1,10-on-1,20-on-1的方式测试经污染后的熔石英基底的损伤阈值,并采用光学显微镜观察损伤形貌、CCD在线测量损伤斑尺寸。结果表明:污染后的熔石英基底的损伤主要发生在后表面,而且以热烧蚀和热应力为主,基底的损伤阈值与熔石英前表面污染颗粒尺寸呈负指数关系,随后表面污染物颗粒尺寸的增大呈略微下降。前表面颗粒污染物诱导损伤斑尺寸为颗粒污染物尺寸的4倍,后表面颗粒污染物引起的损伤斑尺寸约为颗粒污染物尺寸的2倍。并绘出损伤斑尺寸与颗粒尺寸、辐照方式之间的关系。     

基于激光近场和图像分割技术的复合波长诱导熔石英损伤实验研究

在复合波长(波长分别为1053、527、351nm)情况下,利用激光近场对熔石英样品进行损伤实验。设计了一种基于激光近场辐照的损伤阈值定义方法,并利用带有灰度抑制的分水岭标记算法对损伤图像进行损伤区域提取,通过对比损伤图像与相应光束近场能量分布,计算出损伤区域与非损伤区域临界处的光能量密度,即为熔石英样品的损伤阈值。实验结果表明,复合波长激光诱导熔石英损伤是3种波长激光共同作用的结果,但351nm激光对损伤起主要作用,初始损伤阈值为8.22J/cm2;在复合波长激光多次辐照样品的情况下,熔石英样品后表面的损伤成指数形式增长,损伤增长系数为0.59。     

熔石英表面铜膜污染物诱导损伤实验研究

 在熔石英元件表面溅射一层厚度小于10 nm的金属铜膜污染物,并测试元件的透过率。测试355 nm熔石英元件的激光损伤阈值,并用光学显微镜观测损伤形态。实验结果表明：污染后的熔石英元件的损伤阈值降低20%左右,元件表面的金属污染物薄膜经强激光辐照,在熔石英表面形成很多坑状微损伤,分布不均的热应力导致表面起伏,并有明显的烧蚀现象,导致基底损伤阈值下降。建立的光吸收和热沉积传输模型初步解释污染物膜层导致熔石英元件损伤的机理。     

杂质诱导熔石英激光的损伤机理

发展了355 nm纳秒激光下亚波长杂质粒子引起熔石英损伤的基本模型。通过Mie散射理论和热传导方程,计算了粒子与熔石英边界处的温度随粒子尺寸的变化关系,并分析了达到临界温度时,不同粒子诱导损伤所需的关键能量密度,讨论了各粒子最易引起熔石英损伤的尺寸。实验采用355 nm纳秒激光脉冲作用熔石英及其HF刻蚀样品,测得两者的损伤概率。研究表明:粒子吸收激光能量,随着粒子半径的增加,其边缘温度先增大后减小,一定尺寸范围内的粒子才会引起熔石英的损伤;关键能量密度所对应的粒子半径为最易引起熔石英损伤的关键粒子半径;经刻蚀后,熔石英样品表面杂质数密度降低,损伤概率降低,损伤阈值提高。     

熔石英表面热致应力对激光损伤行为影响的研究

为了研究热致应力对光学元件损伤特性的影响,通过实验测试退火处理消除热应力和未消热应力石英基片的激光损伤特性,研究了热致应力对石英元件初始损伤阈值、损伤增长阈值以及损伤增长规律的影响.结果表明,热致应力对熔石英光学元件的初始损伤阈值有影响,初始损伤阈值随着热致应力增大而降低;热致应力会加剧激光引发的损伤增长,相同的激光通量下,表面应力越大的区域拥有越高的损伤增长因子,但损伤增长仍遵从指数增长规律.热致应力对损伤增长阈值没有明显的影响.本文的研究将为CO2激光预处理工艺能否被应用于大口径光学元件提供一个必要的技术参考.     

Surface evolution and laser damage resistance of CO2 laser irradiated area of fused silica

A 10.6 μm CO₂ laser has been reported to effectively mitigate the laser damage growth of fused silica. Two zones of the laser irradiated area are defined in this work: the distorted zone and the laser affected zone. The parameters of the two zones are studied at different CO₂ laser beam sizes, irradiation times, and powers by microscopy, profilometry, and photoelastic method. The results show that the diameter of laser affected zone is almost completely determined by the laser beam size and the distorted zone is associated with the mitigation range of CO₂ laser beam. The diameter and depth of the distorted zone increase as the laser power and irradiation time increase. The depth grows exponentially depending on the irradiation time. The maximum residual stress discrepancy is located near the boundary of the laser affected zone. The laser damage resistance test results show that the distorted zone and the laser affected zone have a better damage resistance than the original substrate.     

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.     

Irradiation effects of CO2 laser parameters on surface morphology of fused silica

To understand the surface morphology evolution of fused silica induced by 10.6-μm CO2 laser irradiation at different parameters,this paper reports that optical microscopy,profilometry,and hydrophilicity tests are utilized to characterize the surface structure and roughness of the laser irradiated area. The results show that three typical surface morphologies and two typical hydrophilicity test images are observed at different laser powers and pulse durations. The correlations between surface temperature and surface morphology as well as hydrophilicity behaviours are presented. The different hydrophilicity behaviours are related to surface structures of the laser-induced crater and thermal diffusion area. The thermal diffusion length monotonously increases with increasing laser power and pulse duration. The crater width is almost determined by the laser beam size. The crater depth is more sensitive to the laser power and pulse duration than the crater width.     

CO2激光局域辐照对熔石英损伤特性的影响

研究了CO₂激光局域辐照对熔石英损伤特性的影响, 发现当辐照中心温度较低时(1139 K), 辐照对损伤阈值没有明显影响, 但辐照中心温度较高时(1638 K), 辐照对损伤阈值有明显的影响, 损伤阈值随距离辐照中心间距的增大而减小, 在残余应力产生光程差最大处附近, 损伤阈值降到最小, 随着与辐照中心间距的进一步增加, 损伤阈值略有上升. 对导致此现象的原因做了分析. 由于残余应力的存在, 在辐照中心发生再损伤产生的裂纹后, 裂纹先沿径向扩展, 在残余应力产生光程差最大处附近, 裂纹转而向切向扩展, 这可能与径向和环向张应力随半径的变化有关. 在采用热处理炉退火消除残余应力时, 必须注意元件的洁净处理, 否则退火会出现析晶现象, 对损伤阈值和透射率造成不良影响. 关键词： 2激光局域辐照')" href="#">CO₂激光局域辐照 熔石英 损伤特性     

紫外准分子激光损伤典型光学材料的特性分析

根据已经建立的紫外准分子激光损伤典型光学材料的理论模型,研究了准分子激光对透明光学材料（石英玻璃）和非透明光学材料（K9玻璃）的损伤特性,并结合实验结果证实了理论模型的有效性。研究表明：在准分子激光对非透明光学材料辐照下,激光光斑半径越大,产生的热应力和温度越小;脉宽越小,产生的热应力越大;随着脉冲数的增加,温度和热应力都逐渐增大。值得注意的是,当重频增加至45 Hz以上时,熔融损伤阈值开始低于应力损伤阈值,这说明当重频增加到一定程度时,非透明光学材料将首先产生熔融损伤,而不再是应力损伤。在准分子激光对透明光学材料辐照下,杂质微粒的半径和掩埋深度对光学材料温度场分布有着重要影响。但当杂质半径和掩埋深度超过一定的数值时,杂质粒子的存在与表面温度并无联系。理论模型能够较好地解释石英玻璃前/后表面相同的初始损伤形貌特征。     

铜膜和铁膜污染物诱导熔石英表面损伤行为的对比研究

采用人工溅射的方式分别在熔石英基片上镀制了光学厚度相近的铜膜和铁膜污染物。研究了熔石英基底在355nm波长的激光损伤阈值。分别采用透射式光热透镜技术、椭偏仪、原子力显微镜和光学显微镜研究了两类薄膜的热吸收、膜层厚度、表面微观形貌以及激光辐照后薄膜的损伤形貌。实验结果表明：熔石英表面的金属膜状污染物均导致基片损伤阈值下降,位于前表面的污染物引起的损伤阈值下降更为严重,约为23％。两种污染物薄膜引起基底的损伤形貌、基底损伤阈值的下降幅度与薄膜的热吸收系数与微观结构有关。从热力学响应角度,结合损伤形貌对污染物诱导熔石英表面形貌的损伤机理进行了讨论。     

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.