光学薄膜激光损伤的光热偏转法实时研究

本文首次把调制与脉冲光热偏转技术同时置于激光损伤测试装置之中,用以进行光学薄膜激光损伤的实时研究.初步实验结果表明,该方法不仅有助于确定损伤阀值,也有助于分析损伤形貌和损伤过程,包括样品损伤前的行为及样品在重复频率激光作用下损伤的累积效应.     

聚焦光在亚表面损伤介质中的散射特性

针对光学元件的亚表面缺陷,结合基于激光共焦层析的亚表层检测方法,建立聚焦光束在亚表面损伤介质中的传输模型,并采用有限元分析方法,仿真研究K9玻璃光学元件亚表层缺陷对聚焦光束的散射调制特性,特别对颗粒状和微裂纹两类特殊缺陷的光学调制特性进行研究和分析,探索了波长、缺陷大小、缺陷折射率及缺陷方向对聚焦光束散射特性的影响规律,通过分析包含亚表面损伤缺陷信息的光场分布图和强度变化曲线,获得了亚表面损伤缺陷的信息,并对其进行评价。     

多脉冲激光辐照下介质损伤理论研究

针对纳秒脉冲和飞秒脉冲不同的损伤机制,分别建立了两种多脉冲激光损伤模型。脉宽小于10 ps时,损伤是由于等离子体形成造成介质发生烧蚀所致,对此建立了基于电子密度演化方程的介质击穿模型;脉宽大于100 ps时,损伤是由于热沉积造成介质发生熔融所致,对此建立了基于傅里叶热传导方程的介质热损伤模型。通过计算两种模型下激光参数和材料参数对多脉冲损伤的影响,发现由于损伤机理不同,不同参数对单脉冲损伤阈值和多脉冲损伤阈值的影响趋势不完全一致,敏感程度也不同。通过计算得到了与实验结果一致的多脉冲损伤阈值与脉冲数间关系,使定量预估多脉冲损伤阈值和元件使用寿命成为可能。     

Concerning the impact of polishing induced contamination of fused silica optics on the laser-induced damage density at 351 nm

We analyze the effect of polishing induced contaminants on the laser-induced damage density at the wavelength of 351 nm. Fused silica polished parts were manufactured using various polishing processes. If previous works have shown that high polishing induced cerium content leads to high laser-induced damage density, we show that for low cerium content, there is no correlation between the amount of polishing induced cerium contamination in the part interface and the damage density. This can be also extended to other polishing induced contaminants. These results provide new information for the understanding of laser damage initiation.     

Detection of early stage damage in carbon fiber reinforced polymers for aeronautical applications using an HTS SQUID magnetometer

We present an experimental characterization of multidirectional fibre composites based on eddy current testing using HTS dc SQUID (Superconducting Quantum Interference Device) magnetometers. The correlation between the mechanical tolerance of CFRPs with different thickness and the phase gradient of the magnetic field generated by damage is shown. The eddy current based SQUID NDE is used to detect damage not visible to the naked eye and to study the effect of an impact far from the point of impact. The aim of this work is to demonstrate the capability of our technique to provide information on early stage damage due to an impact process in an unshielded environment.     

多波长激光同时辐照下熔石英元件的损伤研究

对比研究了3ω单独辐照、3ω＋2ω和3ω＋1ω双波长同时辐照下熔石英元件的初始损伤和损伤增长规律，重点研究3ω能量密度在其阈值附近时，低能量密度的2ω和1ω对初始损伤和损伤增长的影响，分析了波长间的能量耦合效应。结果表明:双波长同时辐照下，当2ω和1ω能量密度远低于其自身阈值时，它们对初始损伤几率和损伤增长阈值的影响可以忽略，但也会参与初始损伤和损伤增长过程，会增加初始损伤程度和损伤增长系数。基于飞秒双脉冲成像的冲击波速度测量表明，3ω和1ω同时辐照下，波长间的能量耦合效应会促进激光能量向材料沉积的效率。     

Laser-induced defects in optical multilayer coatings by the spatial resolved method

The spatial resolved method, which measures the laser-induced damage fluence by identifying the location of the damage point in the Gaussian beam three-dimensional direction, is demonstrated. The advantages and practicality of this method have been explained. Taking a triple frequency beam splitter as an example, the defect damage fluence can be accurately calculated by the spatial resolved method. The different defect damage performance of the triple frequency splitter is distinguished under irradiations of only the 355 and 532 nm lasers. The spatial resolved method provides a way to obtain precise information of optical film defect information.     

Impact of organic contamination on the laser-induced damage in vacuum

The impact of two organic contaminations on the damage characteristics of anti-reflector (AR) at 1064 nm is investigated. Contamination experiments were made with toluene and acetone in liquid phase on the surface of AR coatings. Chemical and morphological characterization methods were used to identify and understand the damage process. The possible damage process is analyzed and discussed. It is found that toluene decreases laser-induced damage threshold and acetone seems to be benign and has little influence on laser-induced damage threshold due to its quickly spreading into the coating. Adsorption and droplet micro-lensing effect mechanism are the main cause of enhanced laser-induced damage of toluene.     

Characteristics of nodular defect in HfO2/SiO2 multilayer optical coatings

Laser-induced damage is associated with nodular defects in HfO₂/SiO₂ multilayer films. In order to investigate the damage characteristics of HfO₂/SiO₂ multilayer mirrors and find the information of improving laser-induced damage threshold, nodular defects are characterized by multiple analytical techniques; the damage morphologies induced by nodular-ejections are presented; the depths of nodular-ejection pits are investigated; the laser-induced damage threshold of zero probability and the stabilities of nodular-ejection pits exposed to repetitive illuminations are studied. Results show that domes in the film surface are nodular defects. Reliable depth information of nodular-ejection pits is obtained by counting layers from the damage edge. The depth statistical result implies nodular defects in these samples are usually originated from deep seeds. Some process optimizations suggestions are given based on the depth information. A simple tractable method is proposed to determine the functional damage threshold of these HfO₂/SiO₂ multilayer films basing on the damage experiments.     

Application of infrared lock-in thermography for the quantitative evaluation of bruises on pears

An infrared lock-in thermography technique was adjusted for the detection of early bruises on pears. This mechanical damage is usually difficult to detect in the early stage after harvested using conventional visual sorting or CCD sensor-based imaging processing methods. We measured the thermal emission signals from pears using a highly sensitive mid-infrared thermal camera. These images were post-processed using a lock-in method that utilized the periodic thermal energy input to the pear. By applying the lock-in method to infrared thermography, the detection sensitivity and signal to noise ratio were enhanced because of the phase-sensitive narrow-band filtering effect. It was also found that the phase information of thermal emission from pears provides good metrics with which to identify quantitative information about both damage size and damage depth for pears. Additionally, a photothermal model was implemented to investigate the behavior of thermal waves on pears under convective conditions. Theoretical results were compared to experimental results. These results suggested that the proposed lock-in thermography technique and resultant phase information can be used to detect mechanical damage to fruit, especially in the early stage of bruising.     

化学增透膜激光疲劳损伤效应

疲劳效应是诱导高功率固体激光装置中光学元件激光损伤的因素之一,目前对SiO₂化学增透膜激光诱导疲劳损伤的研究鲜见报道。基于此,本文采用单一激光能量多发次辐照和多梯度激光能量多发次辐照两种不同的激光辐照方式,研究1064 nm化学增透膜层的激光疲劳损伤效应及特征。研究结果表明,在单一激光能量多发次脉冲激光辐照下,膜层最易发生疲劳损伤; 采用多梯度激光能量多发次辐照的方式,可以有效地提升膜层的损伤阈值,进而提升膜层的抗激光疲劳损伤性能。     

Laser-induced damage studies in GaAs

Laser-induced damage studies have been carried out on monocrystal GaAs at 1.06 μm wavelength as a function of pulse repetition rate in the nanosecond regime. The single shot observed laser damage threshold is 0.9 J/cm². It has been found that the damage threshold decreases when the sample is irradiated with large number of pulses. However, the above effect is observed only when the repetition rate is higher than 1 Hz. Various laser damage mechanism theories have been discussed to explain the results.     

Some aspects on 3D numerical modeling of high velocity impact of particles in cold spraying by explicit finite element analysis

Three-dimensional modeling of particle impacting behavior in cold spraying by using ABAQUS/Explicit was conducted for copper and other materials. Various combinations of calculation settings concerning material damage, Arbitrary Lagrangian Eulerian adaptive meshing, distortion control and contact interaction were examined. The effects of meshing size and particle size on the impact behavior were analyzed compared to the previous results. The results show that the simulations with material damage cope well with the element excessive distortion and the resultant output is more reasonable than that obtained without material damage. In addition, the meshing size has less effect on the output with the material damage than without material damage. Although particle size has little effect on the morphologies of the deformed particles, it has some effect on the failure of elements at contact interfaces. The critical velocity for particle deposition could be estimated given the appropriate material properties.     

Damage distribution and measure of projected range in proton bombarded GaAs

Abstract

The technique of cross-sectional transmission electron microscopy has been applied to obtain information on the projected range of protons and their damage distribution in gallium arsenide. The crystals were subjected to dosages of 1 × 10¹⁵ to 1 × 10¹⁷ protons cm^?2 and proton energies of 100, 200 and 300 keV. Within this energy range the damage shows a Gaussian distribution about a mean range which correlates closely with LSS values. The experimentally determined damage profiles are found to be essentially independent of proton energy and the temperature of post implantation anneal for a given dosage. The displacement damage as reflected by the damage profiles is found to be linear with proton dose. Finally, it is estimated that defects became visible in unannealed crystals when each atom is, on the average, displaced at least once during irradiation.     

532nm皮秒脉冲激光对单晶硅的损伤特性研究

随着光电对抗和超短脉冲激光技术的发展,研究超短脉冲激光与单晶硅相互作用具有非常重要的理论和实际意义.为了进一步明确532 nm皮秒脉冲激光对单晶硅的损伤机理,本文开展了532 nm皮秒脉冲激光辐照单晶硅的损伤效应实验研究,测定了损伤阈值,明确了损伤机理,探讨了低通量下的脉冲累积效应.首先,利用波长为532 nm、脉冲宽...     

In situ investigation of synchrotron radiation damage effect of ancient paintings by time-resolved ED-XAS and IR combined techniques

Advanced synchrotron radiation light is a powerful tool for archaeometry research. However, its applications to precious cultural relics, especially for color painting, have been hindered to some degree due to potential X-ray radiation damage. Compared to inorganic mineral pigments, organic binders in the painting are easier to be damaged by synchrotron radiation X-ray beam. The radiation damage effect of two typical painting samples, pure rabbit skin glue and the mixed sample of rabbit skin glue and zinc white, has been investigated by in situ time-resolved ED-XAS and IR combined techniques. The results show that the radiation damage effect of pure rabbit skin glue is more serious at low X-ray energy (7775 eV). The radiation damage effect of the mixed sample increases significantly due to more X-ray absorption by inorganic pigments. Furthermore, the radiation damage is more serious at the energy near Zn K-edge and is somewhat slight at higher energy (13,054 eV). These damages are more obvious from the point of view of protein secondary structures. The irradiation damage effects increase more rapidly at the beginning and are not linear with the irradiating time. The results indicate that synchrotron radiation damage can be reduced effectively by using X-ray energy far away from the X-ray absorption edge of the major element in the pigments during XRF, XRD and CT experiments, or by using time-resolved techniques such as QXAFS and ED-XAS during XAFS experiments.     

Damage spreading and criticality in finite random dynamical networks

We systematically study and compare damage spreading at the sparse percolation (SP) limit for random Boolean and threshold networks with perturbations that are independent of the network size N. This limit is relevant to information and damage propagation in many technological and natural networks. Using finite-size scaling, we identify a new characteristic connectivity Ks, at which the average number of damaged nodes d[over ], after a large number of dynamical updates, is independent of N. Based on marginal damage spreading, we determine the critical connectivity Kc(sparse)(N) for finite N at the SP limit and show that it systematically deviates from Kc, established by the annealed approximation, even for large system sizes. Our findings can potentially explain the results recently obtained for gene regulatory networks and have important implications for the evolution of dynamical networks that solve specific tasks.     

Thermal Neutron damage in cadmium

The isochronal annealing of the damage produced by thermal neutron irradiation of cadmium at 3.6 °K has been studied for several initial doses which vary by a factor of 1000. The recovery results show a strong dependence upon initial dose. This effect, which is not seen to this extent in the fcc metals, cannot be accounted for by an irradiation annealing mechanism. In contrast to the observation of two processes involving long range defect migration for several fcc metals only one process, at high temperatures, is discernable from isochronal annealing of Cd. The presence of another process at low temperatures is clearly established by other means. Irradiation annealing effects observed during the production of damage at high defect concentrations indicate that the spontaneous annihilation volume between the defects of a new capture event and the defects from an earlier event is 80 atomic volumes. Other results suggest that damage production and recovery mechanisms may be associated with the anisotropic nature of the cadmium hexagonal lattice.     

重复率激光作用下光学薄膜损伤的累积效应

使用脉宽12 ns,频率10 Hz的1064 nm调Q NdYAG激光器,研究了高反射膜在重复率激光作用下的损伤的累积效应.实验发现,高反射膜的损伤阈值随辐照脉冲数增加而降低,表现出明显的累积效应.通过对损伤阈值和损伤概率以及辐照次数的统计性研究,并结合单脉冲辐照的结果,说明了存在于薄膜中微小的缺陷参与了多脉冲激光对薄膜的损伤过程.可用预损伤机制解释实验结果.得到了关于IBS制备的高反射膜的损伤阈值和照射次数的关系式,并用实验结果进行验证,发现具有很好的一致性.实验过程中样品的损伤形貌通过Nomarski偏光显微镜进行了观察,发现是典型的缺陷损伤.     

Structural damage measure index based on non-probabilistic reliability model

Uncertainties in the structural model and measurement data affect structural condition assessment in practice. As the probabilistic information of these uncertainties lacks, the non-probabilistic interval analysis framework is developed to quantify the interval of the structural element stiffness parameters. According to the interval intersection of the element stiffness parameters in the undamaged and damaged states, the possibility of damage existence is defined based on the reliability theory. A damage measure index is then proposed as the product of the nominal stiffness reduction and the defined possibility of damage existence. This new index simultaneously reflects the damage severity and possibility of damage at each structural component. Numerical and experimental examples are presented to illustrate the validity and applicability of the method. The results show that the proposed method can improve the accuracy of damage diagnosis compared with the deterministic damage identification method.