杂质对溶胶-凝胶SiO2薄膜激光损伤的影响

采用溶胶-凝胶法制备了含有吸收性杂质和非吸收性杂质的SiO2增透膜,采用波长为1 064 nm的激光对其进行了小光斑激光预处理,对比研究了预处理前后的激光损伤差异,研究表明：激光预处理对于洁净的SiO2薄膜影响不大;含10 μm SiO2颗粒杂质的样品微透镜效应很明显,容易成为损伤起始的种子,激光预处理后情况有所改善;含有CeO2颗粒杂质的样品表现出了很强的吸收性质,损伤阈值降低到不足洁净样品的一半。所有样品激光预处理后损伤形貌未发生变化,透光率峰值均有约50 nm的蓝移。     

Impact of organic contamination on laser-induced damage threshold of high reflectance coatings in vacuum

The influence of organic contamination in vacuum on the laser-induced damage threshold (LIDT) of coatings is studied. TiO₂/SiO₂ dielectric mirrors with high reflection at 1064 nm are deposited by the electron beam evaporation method. The LIDTs of mirrors are measured in vacuum and atmosphere, respectively. It is found that the contamination in vacuum is easily attracted to optical surfaces because of the low pressure and becomes the source of damage. LIDTs of mirrors have a little change in vacuum compared with in atmosphere when the organic contamination is wiped off. The results indicate that organic contamination is a significant reason to decrease the LIDT. N₂ molecules in vacuum can reduce the influence of the organic contaminations and prtectect high reflectance coatings.     

杂质对溶胶-凝胶SiO2薄膜激光损伤的影响

 采用溶胶-凝胶法制备了含有吸收性杂质和非吸收性杂质的SiO₂增透膜,采用波长为1 064 nm的激光对其进行了小光斑激光预处理,对比研究了预处理前后的激光损伤差异,研究表明：激光预处理对于洁净的SiO₂薄膜影响不大;含10 μm SiO₂颗粒杂质的样品微透镜效应很明显,容易成为损伤起始的种子,激光预处理后情况有所改善;含有CeO₂颗粒杂质的样品表现出了很强的吸收性质,损伤阈值降低到不足洁净样品的一半。所有样品激光预处理后损伤形貌未发生变化,透光率峰值均有约50 nm的蓝移。     

Stress, absorptance and laser-induced damage threshold properties of 355-nm HR coatings

A number of 355-nm Al₂O₃/MgF₂ high-reflectance (HR) coatings were prepared by electron-beam evaporation. The influences of the number of coating layers and deposition temperature on the 355-nm Al₂O₃/MgF₂ HR coatings were investigated. The stress was measured by viewing the substrate deformation before and after coating deposition using an optical interferometer. The laser-induced damage threshold (LIDT) of the samples was measured by a 355-nm Nd:YAG laser with a pulse width of 8 ns. Transmittance and reflectance of the samples were measured by a Lambda 900 spectrometer. It was found that absorptance was the main reason to result in a low LIDT of 355-nm Al₂O₃/MgF₂ HR coatings. The stress in Al₂O₃/MgF₂ HR coatings played an unimportant role in the LIDT, although MgF₂ is known to have high tensile stress.     

Overcoat dependence of laser-induced damage threshold of 355 nm HR coatings

A series of HR coatings, with and without overcoat, were prepared by electron beam evaporation using the same deposition process. The laser-induced damage threshold (LIDT) was measured by a 355 nm Nd:YAG laser with a pulse width of 8 ns. Damage morphologies of samples were observed by Leica-DMRXE Microscope. The stress was measured by viewing the substrate deformation before and after coatings deposition using an optical interferometer. Reflectance of the samples was measured by Lambda 900 Spectrometer. The theoretical results of electric field distributions of the samples were calculate by thin film design software (TFCalc). It was found that SiO₂ overcoat had improved the LIDT greatly, while MgF₂ overcoat had little effect on the LIDT because of its high stress in the HR coatings. The damage morphologies were different among HR coatings with and without overcoats.     

HfO_2单层膜的吸收和激光损伤阈值测试

薄膜吸收是降低膜层激光损伤阈值的重要原因,为了研究薄膜吸收对激光损伤阈值的影响,对HfO2单层膜在1 064 nm处的吸收及其在不同波长激光辐照下的损伤阈值进行了测试和分析。研究结果表明:薄膜的激光损伤阈值由薄膜吸收平均值(决定于薄膜中缺陷的种类和数量)和吸收均匀性(决定于薄膜中缺陷的分布)共同决定;根据HfO2单层膜在1064 nm波长处的吸收值,不但可以定性判断薄膜在1 064 nm波长,而且还可以判断在其它波长激光辐照下的抗激光损伤能力。     

Preparation of sol-gel ZrO2-SiO2 highly reflective multilayer films and laser-induced damage threshold characteristic

Sol-gel (ZrO₂/SiO₂)¹² ZrO₂ films were prepared by spin coating method. The reflectivity spectrum of the films was measured with a Lambda 900 spectrometer. In order to investigate laser-induced damage threshold (LIDT) characteristic of highly reflective films, one-layer ZrO₂ and SiO₂ films, two-layer ZrO₂/SiO₂ and SiO₂/ZrO₂ films were also prepared by spin coating method. LIDT of each film was measured. Damage morphology after laser irradiation was characterized by optical microscopy (Nikon E600K). The experimental results showed that the reflectivity of (ZrO₂/SiO₂)¹² ZrO₂ film at 1064 nm and 355 nm wavelength is 99.7%. The LIDT results decreases as the number of layer of films increases. All the films have similar damage morphology. The experimental results are explained by the different temperature profiles of the films.     

高抗激光损伤阈值介孔SiO2 减反射膜

 用P123作模板剂,通过正硅酸乙酯的水解缩聚和溶剂蒸发自组装过程在K9玻璃上制备介孔SiO₂膜。应用FT-IR,XRD,N₂ 吸附-脱附,AFM和UV-Vis表征手段研究了薄膜的介孔结构和光学性能,并使用“R-on-1”模式,以Nd:YAG脉冲激光（9.2 ns, 1 064 nm）测试了薄膜的激光损伤阈值。结果表明:所镀制单层介孔SiO₂膜具有规整的2D p6 mm长周期结构,为SBA-15型,膜层表面比较平整（均方根粗糙度为2.923 nm）,在1 064 nm处的透过率为99.5%, 换算为激光脉宽为1 ns时,膜层的激光损伤阈值为21.6 J/cm²,显示出了较好的减反性能和抗激光损伤性能。     

退火对ZrO2薄膜微结构及激光损伤阈值的影响

利用电子束蒸发方法在Yb∶YAG晶体和熔融石英衬底上沉积单层ZrO2薄膜,分别在673 K和1 073 K的温度下经过12 h退火以后,通过X射线衍射（XRD）分析了薄膜晶相,计算了薄膜的晶粒尺寸;利用表面热透镜技术获得了薄膜的吸收;测量了退火后薄膜的激光损伤阈值。实验结果表明：两种衬底上的薄膜结构受到退火温度和衬底表面结构的影响,高温退火有利于单斜相的形成,含单斜相的ZrO2薄膜具有较高的激光损伤阈值,而由于衬底的吸收,Yb∶YAG晶体上薄膜的损伤阈值远小于石英衬底上薄膜的损伤阈值。     

退火对ZrO2薄膜微结构及激光损伤阈值的影响

利用电子束蒸发方法在Yb∶YAG晶体和熔融石英衬底上沉积单层ZrO2薄膜,分别在673 K和1 073 K的温度下经过12 h退火以后,通过X射线衍射（XRD）分析了薄膜晶相,计算了薄膜的晶粒尺寸;利用表面热透镜技术获得了薄膜的吸收;测量了退火后薄膜的激光损伤阈值。实验结果表明:两种衬底上的薄膜结构受到退火温度和衬底表面结构的影响,高温退火有利于单斜相的形成,含单斜相的ZrO2薄膜具有较高的激光损伤阈值,而由于衬底的吸收,Yb∶YAG晶体上薄膜的损伤阈值远小于石英衬底上薄膜的损伤阈值。     

高功率激光诱导光学元件损伤阈值测量的不确定度分析

 激光诱导损伤阈值作为一实验参量,对其结果作不确定度分析有利于激光工作者在某个精度范围内获知该参量的信息。从激光损伤和损伤阈值定义出发,分析了基于ISO11254的损伤几率测试法测试激光诱导损伤阈值的不确定度来源,包括激光能量测量、激光光斑有效面积测量、各能量密度处损伤几率的计算以及对损伤几率点进行直线拟合这4个方面。并利用统计学原理和线性拟合等理论对这4个方面引起的不确定度分量及最终测试结果的相对合成不确定度进行了计算。以1 064 nm高反薄膜样品为例,分析表明：损伤几率点的计算和几率图中损伤几率的直线拟合是损伤阈值测试结果不确定度的主要来源,当样品的损伤阈值为7.79 J/cm²时,这两种因素引起的相对不确定度可分别在4%和18%左右,损伤阈值的相对合成不确定度达18.72%。     

高功率激光诱导光学元件损伤阈值测量的不确定度分析

激光诱导损伤阈值作为一实验参量,对其结果作不确定度分析有利于激光工作者在某个精度范围内获知该参量的信息。从激光损伤和损伤阈值定义出发,分析了基于ISO11254的损伤几率测试法测试激光诱导损伤阈值的不确定度来源,包括激光能量测量、激光光斑有效面积测量、各能量密度处损伤几率的计算以及对损伤几率点进行直线拟合这4个方面。并利用统计学原理和线性拟合等理论对这4个方面引起的不确定度分量及最终测试结果的相对合成不确定度进行了计算。以1 064 nm高反薄膜样品为例,分析表明：损伤几率点的计算和几率图中损伤几率的直线拟合是损伤阈值测试结果不确定度的主要来源,当样品的损伤阈值为7.79 J/cm2时,这两种因素引起的相对不确定度可分别在4%和18%左右,损伤阈值的相对合成不确定度达18.72%。     

微观缺陷对材料损伤阈值的影响分析

为了研究材料表面高频缺陷对损伤阈值的影响规律,针对典型表面圆锥凸起状表面缺陷建立了三维分析模型,使用有限元算法计算了两种不同波长激光辐照下,表面缺陷周围的电场变化规律。基于激光诱导材料产生损伤的场效应理论,对缺陷存在条件下材料的损伤阈值进行了定量计算。结果表明,缺陷的存在会对电场产生明显的放大效应,这将直接导致损伤阈值的下降;损伤阈值与缺陷高度成反比关系,与入射波长成正比关系;缺陷导致的损伤阈值下降幅度会随脉宽增加先减小后增大,当入射波长分别为351 nm和1064 nm时,缺陷导致的损伤阈值下降幅度分别在脉宽为1.80 ps和15.80 ps处最小。     

清洗对偏振分光膜损伤阈值的影响

采用微分干涉显微镜、扫描电镜和聚焦离子束观察了偏振分光膜损伤的形貌,从损伤机理出发,研究了清洗对偏振分光膜损伤阈值的影响。结果表明：清洗能有效去除表面杂质,清洗质量越好,基板上的杂质尺寸越小,杂质密度也越小,相应的偏振分光膜S光的损伤阈值越高;清洗能有效去除基板表面的纳米吸收中心,吸收性杂质分布密度越小,吸收峰越低,P光的损伤阈值越高。     

微观缺陷对材料损伤阈值的影响分析

为了研究材料表面高频缺陷对损伤阈值的影响规律,针对典型表面圆锥凸起状表面缺陷建立了三维分析模型,使用有限元算法计算了两种不同波长激光辐照下,表面缺陷周围的电场变化规律。基于激光诱导材料产生损伤的场效应理论,对缺陷存在条件下材料的损伤阈值进行了定量计算。结果表明,缺陷的存在会对电场产生明显的放大效应,这将直接导致损伤阈值的下降;损伤阈值与缺陷高度成反比关系,与入射波长成正比关系;缺陷导致的损伤阈值下降幅度会随脉宽增加先减小后增大,当入射波长分别为351nm和1064nm时,缺陷导致的损伤阈值下降幅度分别在脉宽为1.80ps和15.80ps处最小。     

溶胶-凝胶ZrO2-TiO2高折射率光学膜层的抗激光损伤性能研究

采用溶胶-凝胶方法制备了ZrO2-TiO2(Ti含量为0-100 mol%)高折射率光学薄膜.借助激光动态光散射技术研究溶胶微结构.采用傅里叶变换红外光谱、原子力显微镜、薄膜光学常数分析仪、漫反射吸收光谱及强激光辐照实验,对膜层的结构、光学性能及抗激光损伤性能进行了系统表征.结果显示,溶胶-凝胶工艺可以在部分牺牲折射率的情况下,使膜层的抗激光损伤性能得到大幅度提升.随Ti含量从0mol%增加至100 mol%,膜层的平均损伤阈值呈下降趋势,当Ti含量从0mol%增加至60mol%时,平均损伤阈值从57.1 J/cm2下降到21.1 J/cm2(辐照激光波长为1053 nm,脉冲宽度为10 ns,"R/1"测试模式),当Ti含量从60mol%增加至100mol%时,平均损伤阈值变化很小.综合溶胶微结构、膜层光学性能和损伤实验结果可以推断,强激光诱导多光子吸收是引起膜层损伤的主要原因.不同配比的复合膜之间光学带隙的显著差异导致相同辐照激光情况下多光子吸收的概率发生变化,从而导致损伤阈值的规律性变化.     

Ultraviolet laser-induced damage on fused silica substrate and its sol-gel coating

A comparative study of the laser-induced damage thresholds (LIDTs) of fused silica substrates and their sol-gel silica coatings was carried out with 355 nm laser irradiation. Chemical etching and superpolishing were employed in different ways to improve the substrate. The laser damage tests showed that the coated substrate was no more susceptible to laser damage than the bare substrate, showing that the substrate quality was the dominant factor limiting the LIDT for UV irradiation. In addition, it was found that high value of substrate microroughness was more harmful to the LIDT of the coated than the bare substrate, and that a proper combination of etching and superpolishing can optimize the LIDT.     

高损伤阈值三倍频分离膜

设计了Nd：YAG激光用三倍频分离膜,膜层材料为SiO2和HfO2。经过优化,膜系在355 nm处的反射率在99%以上,在532 nm和1 064 nm处透射率也在99%以上。采用电子束蒸发技术,在熔融石英基底上制备了样品,经测量,制备的分离膜光学性能与设计值接近。分离膜在355 nm激光辐照下的损伤阈值为5.1 J/cm2,并用微分干涉显微镜表征了薄膜损伤形貌。     

高损伤阈值三倍频分离膜

 设计了Nd：YAG激光用三倍频分离膜,膜层材料为SiO₂和HfO₂。经过优化,膜系在355 nm处的反射率在99%以上,在532 nm和1 064 nm处透射率也在99%以上。采用电子束蒸发技术,在熔融石英基底上制备了样品,经测量,制备的分离膜光学性能与设计值接近。分离膜在355 nm激光辐照下的损伤阈值为5.1 J/cm²,并用微分干涉显微镜表征了薄膜损伤形貌。     

单层SiO2物理膜与化学膜激光损伤机理的对比研究

采用离子束溅射沉积技术和溶胶-凝胶技术在K9基片上镀制了厚度相近的SiO2单层介质膜,用表面热透镜技术对两类膜层分别进行了热吸收及实时动态热畸变实验测试,结合散射光阈值测试及实验前后膜层的显微观测,对相同基底、相同膜层材料而采用不同方法镀制的光学膜层,发现化学膜的强激光损伤阈值远高于相应物理膜;从热力学响应及膜层特性差异的角度揭示了化学膜层的强激光损伤阈值远高于相应物理膜层的微观机理,即物理膜具有高吸收下的致密膜层快传导的基底热冲击效应,而化学膜则有低吸收下的疏松空隙填充慢传导的延缓效应,大量的实验数据及现象都证实了这一结论.