电子束、离子辅助和离子束溅射三种工艺对光学薄膜性能的影响

 运用电子束、离子辅助和离子束溅射三种镀膜工艺分别制备光学薄膜，包括单层氧化物薄膜和增透膜，然后采取一系列测试手段，如Zygo轮廓仪、原子力显微镜、表面热透镜技术和X射线衍射等技术，来分析和研究不同的工艺对这些薄膜性能的不同影响，以判断合理的沉积工艺。     

Subsurface defect characterization and laser-induced damage performance of fused silica optics polished with colloidal silica and ceria

This paper mainly focuses on the influence of colloidal silica polishing on the damage performance of fused silica optics. In this paper, nanometer sized colloidal silica and micron sized ceria are used to polish fused silica optics. The colloidal silica polished samples and ceria polished samples exhibit that the root-mean-squared(RMS) average surface roughness values are 0.7 nm and 1.0 nm, respectively. The subsurface defects and damage performance of the polished optics are analyzed and discussed. It is revealed that colloidal silica polishing will introduce much fewer absorptive contaminant elements and subsurface damages especially no trailing indentation fracture. The 355-nm laser damage test reveals that each of the fused silica samples polished with colloidal silica has a much higher damage threshold and lower damage density than ceria polished samples. Colloidal silica polishing is potential in manufacturing high power laser optics.     

熔石英亚表面划痕激光诱导损伤阈值实验研究

 用原子力显微镜和光学显微镜观测酸蚀后熔石英亚表面划痕,并根据形貌特征将其分为Boussinesq-point-force crack(BPFC)、Hertzian-conical scratch(HCS)和Plastic indent(PI)三类,测试了各类划痕的损伤阈值,讨论了激光损伤机制。结果表明锐度较大的BPFC损伤阈值不超过2.0 J/cm<>2;深度小于1 μm的 HCS阈值可达2.6 J/cm²;形变较大的PI阈值至2.8 J/cm2,形变较小的PI的激光损伤阈值与无缺陷材料相当。BPFC 和深度超过1 μm的HCS是导致熔石英损伤阈值低的主要因素。     

Structural modifications in fused silica induced by ultraviolet fs laser filaments

It is shown that the tight focusing of short ultraviolet laser pulses (248 nm, 450 fs) in the bulk of high bandgap transparent solids (fused silica) can result in structural modifications in the material. These can vary from small changes of the refractive index to birefringence, cracks and voids. This restructuring of the medium is due to the high laser intensities attained, and the plasma that is generated through multi-photon processes. The restructuring comes in the form of a string, which is the result of the nonlinear propagation of the laser beam in the medium as a self-trapped filament. We resume the conditions for the generation of the different types of modifications and comment on the temporal evolution and the role of the plasma strings at the trail of the light filaments.     

Electron beam initiated grafting of methacryloxypropyl-trimethoxysilane to fused silica glass

The effect of electron beam pretreatment of fused silica glass upon its surface functional composition and possibility for subsequent immobilization of methacryloxypropyl-trimethoxysilane (MOPTMS) layer is studied using FTIR spectroscopy and adsorption of acid-base indicators. The content of Brensted acidic centers (silanol groups) on the irradiated fused silica surface is found to follow an “oscillatory” trend as function of the absorbed dose below 100 kGy at electron beam processing due to the alternating reactions of hydroxylation (probably as a result of Si-O-Si bond disruption and interaction with radiolyzed physically adsorbed water) and thermal dehydration/dehydroxylation at radiation heating. The best conditions for MOPTMS layer formation are based on the increased acidity of both silica surface (formation of acidic hydroxyls) and the reaction medium (MOPTMS deposition from acetic acid solution). The optimal value of absorbed dose at electron beam processing providing the highest efficiency of MOPTMS grafting is 50 kGy at accelerated electron energy 700 keV. Electron beam pretreatment of fused silica surface is shown to provide more efficient MOPTMS immobilization in comparison with conventional chemical and thermal grafting procedures. The obtained results are promising for the enhancement of the processes for the production of fused silica glass capillaries for electrochromatography and electrophoresis at the stage of an intermediate bifunctional layer formation required for the subsequent deposition of specific polymer coatings.     

Focused ion beam based sputtering yield measurements on ZnO and Mo thin films

In order to facilitate the lateral structuring of solar cell multilayer structures, the ion beam sputtering behaviour of Mo and ZnO thin films deposited onto soda-lime glass and single crystalline Si substrates was studied. Prior to ion beam processing the layers were analyzed by Energy Dispersive X-Ray Spectrometry (EDS), X-Ray Diffractometry (XRD) and Rutherford Backscattering (RBS). In order to characterize the ion beam sputtering of the investigated layers, 2×2 μm² fractions of the thin films were removed by a scanned 30 keV focused Ga⁺ ion beam (FIB) in a dual beam system. SEM images taken during the milling process allowed continuous monitoring of the process without breaking the vacuum. The depth of the groove after removal of the layers was measured by Atomic Force Microscopy (AFM) and was plotted as a function of the ion dose. The sputtering depth has a dependence on the ion dose that is close to linear. The deviation from linearity is produced by heating effects at high beam currents. Sputtering yield values calculated from the experiments and simulations showed good agreement in the case of Mo but deviation was found in the case of ZnO.     

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.     

Evolution of self-assembled Ge/Si island grown by ion beam sputtering deposition

The effect of temperature and Ge coverage on the evolution of self-assembled Ge/Si islands grown by ion beam sputtering deposition is studied. Atomic force microscopy and Raman spectroscopy are used to analyze the island morphology and the intermixing between Si and Ge. The experiments are presented in two aspects. First, when the temperature is increased, intermixing is promoted, resulting in the reappearance of low aspect ratio islands. Second, a different evolution pathway is observed, in which short islands initially don’t grow along the constant ratio of 11:1 (diameter:height) and the islands always grow faster in vertical direction. In summary, the interdiffusion, surface diffusion, and amount of Ge determines the evolution of Ge/Si islands.     

Latent track creation in fused silica by 200 MeV silver beam

Studies of formation of latent tracks in swift heavy ion irradiated SiO₂ are presented. Fused silica (SiO₂) were irradiated with 200 MeV silver (Ag) ion beam at varying fluences. Radiation-induced effects were studied by ultraviolet(UV)/Visible optical absorption spectroscopy and transmission electron microscopy (TEM). UV/Visible absorption study indicated E′ centers and oxygen deficiency centers having characteristic absorption occurred at 5 eV. The density of these color centers calculated from the absorption peak intensity showed Poisson-type variation with irradiation fluence. The defects are thus entirely confined to the latent tracks created by swift heavy ions in SiO₂. The track radius estimated from optical absorption study was found to be 5.1 nm. Similar results were obtained from TEM studies of the irradiated samples.     

电子束、离子辅助和离子束溅射三种工艺对光学薄膜性能的影响

运用电子束、离子辅助和离子束溅射三种镀膜工艺分别制备光学薄膜,包括单层氧化物薄膜和增透膜,然后采取一系列测试手段,如Zygo轮廓仪、原子力显微镜、表面热透镜技术和X射线衍射等技术,来分析和研究不同的工艺对这些薄膜性能的不同影响,以判断合理的沉积工艺。     

热蒸发与离子束溅射制备LaF3薄膜的光学特性

研究了钼舟热蒸发工艺和离子束溅射方法制备的单层LaF₃薄膜的特性。首先,采用分光光度计测量了LaF₃薄膜的透射率和反射率光谱,使用不同模型拟合得出薄膜的折射率和消光系数。然后,采用应力仪测量了加热和降温过程中LaF₃薄膜的应力-温度曲线。最后,采用X射线衍射仪测试了薄膜的晶体结构。实验结果表明,热蒸发制备的LaF₃（RH LaF₃）存在折射率的不均匀性,在193 nm,其折射率和消光系数分别为1.687和5×10^-4,而离子束溅射制备的LaF₃（IBS LaF₃）折射率和消光系数分别为1.714和9×10^-4。两种薄膜表现出相反的应力状态,RH LaF₃薄膜具有张应力,而IBS LaF₃具有压应力,退火之后其压应力减小。热蒸发制备的MgF₂/LaF₃减反膜在193 nm透过率为99.4%,反射率为0.04%,离子束溅射制备的AlF₃/LaF₃减反膜透过率为99.2%,反射率为0.1%。     

环境气氛压强对熔石英紫外激光损伤阈值的影响

 利用1∶1, S∶1, R∶1方法,测试了不同真空度（10-3～105 Pa）和不同气氛（空气、氮气、氧气）环境下熔石英351 nm激光损伤阈值,测试结果表明,用1∶1, S∶1方法测试得到的阈值在不同气氛压强下几乎相等;R∶1损伤阈值受气压的影响较大,在小于等于10³ Pa气压下,较105 Pa气压的阈值降低28%～41%;但R∶1损伤阈值同气氛的关系不大,在同气压下差别小于10%,在测量值误差范围内。利用50%破坏几率对应的损伤阈值Fth（R∶1）一半的激光能量密度辐照样品,考察其抗多脉冲辐照的能力,分析表明,在同样的能量密度辐照下,10³ Pa空气及氮气环境和105 Pa氮气环境下同样具有高的寿命;而10^-3 Pa高真空环境下其寿命较短,在10^-1 Pa低真空环境下其寿命最短。     

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。     

纳秒激光诱导损伤熔石英玻璃的动力学过程

采用超快时间分辨阴影成像技术研究了纳秒激光诱导损伤熔石英玻璃前后表面和体内的动力学过程,对比分析了前后表面和体内的损伤差异及损伤机制。在前表面,观察了空气和材料中的等离子体和冲击波的产生与发展过程;亚纳秒激光辐照下,前表面材料内观察到三个应力波,并观察到材料体内的损伤过程。在后表面,除观察到冲击波的产生与发展过程,还观察到表面物质的烧蚀去除与喷发过程。在材料内部,损伤由自聚焦和点缺陷吸收两种机制主导,而且点缺陷吸收诱导材料体内损伤有时间先后顺序。     

酸蚀深度对熔石英三倍频激光损伤阈值的影响

 采用干涉仪和台阶仪测试蚀刻深度随时间的变化,结合材料去除速率测量,研究了HF酸蚀液对熔石英表面蚀刻的影响。测试了蚀刻后损伤阈值和表面粗糙度的变化。研究表明,熔石英表面重沉积层厚度约16 nm,亚表面缺陷层大于106 nm;重沉积层去除后损伤阈值增大,随亚表面缺陷层暴露其阈值先降低后又增加,最后趋于稳定;然而,随蚀刻时间的增加,其表面粗糙度增大。分析表明,蚀刻到200 nm能有效地提高熔石英的低损伤阈值,有利于降低初始损伤点数量和提高熔石英表面的机械强度。     

Optical studies of two dimensional gratings in fused silica, GE 124, and Foturan glasses fabricated using femtosecond laser pulses

Herein we present results on the femtosecond laser direct writing and optical characterization studies of two dimensional gratings in fused silica, GE 124, and Foturan^™ glasses. Varieties of structures were achieved with varying input energy and spatial orientation of the samples. Various characterization techniques including fluorescence spectroscopy, micro-Raman spectroscopy, and laser confocal microscopy were employed to analyze the structural and physical modifications at the focal volume resulting in change of refractive index. Diffraction efficiencies of 9–12% were observed from the grating structures. A broad-band emission was observed in the laser-modified region of the Foturan glass. The obtained results are analyzed in the light of recent work in similar glasses and exploring the applications of such structures in the fields of photonics.     

熔石英紫外激光初始损伤形态分析

 采取355 nm激光脉冲辐照熔石英样品,利用Nomarski微分干涉差显微镜、原子力显微镜和扫描电子显微镜观测手段对前后表面产生的损伤点进行了观察分析。对前后表面损伤形态做出详细的描述和分类,从理论上对每种损伤类型产生的条件与机理做出推测。实验结果表明：熔石英前表面存在小麻点群损伤和星状裂纹损伤两种损伤形态,横向尺寸分别为0.8～2.5和1.0～5.5 μm;后表面存在小麻点群损伤、壳状剥离损伤和火山口3种损伤形态,损伤横向尺寸分别为0.48～1.33,4～20和12～30 μm。实验证明了1 μm尺度损伤点的产生与再沉积层密切相关。     

Optical emission spectroscopy by Ar ion sputtering of Ti surface under O2 environment

Visible light emission from atoms and ions sputtered on a polycrystalline Ti surface was observed under irradiation of 30 keV Ar³⁺ ions. A number of atomic lines of Ti I and II were observed in the wavelength of 250-850 nm. The intensity of Ti II emission increased 1.3-5.6 times by introducing oxygen molecules at a pressure of 5.8 × 10⁻⁵ Pa, whereas that of Ti I decreased 0.5-0.8 times. Factors enhancing or reducing photon intensities were plotted as a function of energy of the corresponding electrons in the excited states for Ti atoms and Ti⁺ ions.     

熔石英紫外激光初始损伤形态分析

采取355 nm激光脉冲辐照熔石英样品,利用Nomarski微分干涉差显微镜、原子力显微镜和扫描电子显微镜观测手段对前后表面产生的损伤点进行了观察分析。对前后表面损伤形态做出详细的描述和分类,从理论上对每种损伤类型产生的条件与机理做出推测。实验结果表明：熔石英前表面存在小麻点群损伤和星状裂纹损伤两种损伤形态,横向尺寸分别为0.8～2.5和1.0～5.5 μm;后表面存在小麻点群损伤、壳状剥离损伤和火山口3种损伤形态,损伤横向尺寸分别为0.48～1.33,4～20和12～30 μm。实验证明了1 μm尺度损伤点的产生与再沉积层密切相关。     

Sb_2Te_3热电薄膜的离子束溅射制备与表征

采用离子束溅射技术交替沉积Sb-Te-Sb多层薄膜后进行高真空热处理,直接制备Sb2Te3薄膜.利用X射线衍射(XRD)仪、霍尔系数测试仪、薄膜Seebeck系数测量系统对所制备的薄膜特性进行表征.XRD测量结果显示,薄膜的主要衍射峰与Sb2Te3标准衍射峰相同,在[101]/[012]晶向取向明显,存在较多的Te杂质峰;霍尔系数测试结果表明,薄膜为p型半导体薄膜,薄膜电阻率较低,其电导率接近于金属电导率,载流子浓度量级为1023cm-3,具有良好的电学性能;Seebeck系数测量结果显示,薄膜具有良好的热电性能,在不同条件下制备的薄膜的Seebeck系数在7.8—62μV/K范围;在所制备的薄膜中,退火时间为6h、退火温度为200℃的薄膜其Seebeck系数达到最大,约为62μV/K,且电阻率最小.