一种大入射角容差宽带薄膜偏振器

通过组合长波通和短波通膜堆的方法,设计并制备了一种大入射角容差宽带薄膜偏振器。该薄膜为HfO2/SiO2结构,采用无离子束辅助的电子束蒸发工艺,蒸发金属铪和SiO2制得。对该膜的透射率光谱、激光损伤阈值和形貌进行了研究,结果显示其不仅在1044~1084 nm波段内都具有很高的对比度,而且在1064 nm波长、 53~60的入射角范围内具有很大的消光比和激光损伤阈值,且损伤特性基本不随入射角变化。该偏振器的P光损伤阈值约为20 J/cm2,损伤主要由基板与薄膜界面处的纳米级缺陷所引起;S光损伤阈值约为45 J/cm2,损伤主要由激光辐照下薄膜表面的等离子烧蚀现象引起。     

超低泄漏电流二极管单粒子位移损伤电流计算

提出了一种计算超低泄漏电流硅二极管的单粒子位移损伤电流的方法。采用SRIM软件计算了252Cf源的裂变碎片入射二极管产生的初级撞出原子的分布, 并采用Shockley-Read-Hall复合理论探讨了单粒子位移损伤电流值与缺陷参数的关系, 计算了252Cf源辐照引起的单粒子位移损伤电流台阶值, 计算结果与实验结果一致。针对耗尽区电场非均匀的特点, 提出电场分层近似方法来考虑处于耗尽区中不同位置的初级撞出原子产生的缺陷对泄漏电流的影响。结果表明, PN结附近电场增强载流子产生效应最显著, 考虑电场增强效应的情况下单个Frenkel缺陷引起的泄漏电流比未考虑电场增强效应时高约44倍;裂变碎片80 MeV Nd入射比106 MeV Cd入射引起的单粒子位移损伤电流大;252Cf源的裂变碎片在二极管中引起的单粒子位移损伤电流台阶值主要集中于1 fA至1 pA之间。     

不锈钢电子束收集极的损伤能量密度阈值

对强磁场相对论返波管系统中电子束收集极损伤的主要影响因素进行了分析,通过设计并使用锥面不锈钢收集极,提高了收集极的耐电子束轰击能力。在单次实验条件下,研究了电子束能量密度对不锈钢收集极表面损伤及系统产生微波的影响,结合对无箔二极管中电子束空间密度分布的研究结果,给出了不锈钢收集极损伤电子束能量密度阈值范围。     

一个修正的金属材料低周疲劳损伤模型

疲劳破坏是金属最常见的失效形式之一.基于连续损伤力学理论和能量原理,论文提出了一个修正的金属材料低周疲劳损伤演化方程,该方程综合考虑了材料的塑性强化、微裂纹闭合效应等因素对损伤累积的影响.将修正后的损伤演化方程以UMAT子程序的形式导入有限元计算软件ABAQUS之中,建立了疲劳损伤的计算模型,并以铝合金7050-T7451为例对该模型的有效性和适用性进行了验证.     

水合物分解气体泄漏引起的海床破坏实验研究

海床下水合物分解可能造成大量的生成气体泄漏. 气体渗漏一方面造成海床表层的破坏;另一方面使得海水密度减小造成海上一些结构的安全隐患. 本文通过实验研究泄漏气体在水中上升过程中的扩散行为,以及渗漏对海底粉砂土海床的破坏规律. 考虑压力,盖层厚度在渗漏气体对盖层土体形态破坏的影响,获得了气体在水中上升过程中的扩散角的特点,以及气体泄漏导致的海床冲刷坑范围随气体压力、土层厚度的变化规律,可以为进一步的研究和工程应用提供参考.     

铝合金蚀坑损伤参量评述

将蚀坑损伤参量分成4 类:尺寸、形状、统计和试验参数,回顾了蚀坑深度、投影面积、长宽比、矩形比、表面腐蚀率、分形维数、预腐蚀系数等影响剩余寿命的主要损伤参量,总结了蚀坑等效成初始裂纹的方法.     

渐变折射率Ta2O5/SiO2薄膜多脉冲激光损伤特性

采用离子束溅射（IBS）的方式,制备了1064 nm高反射Ta2O5/SiO2渐变折射率光学薄膜。对其光学性能和在基频多脉冲下抗损伤性能进行了分析。 通过渐变折射率的设计方式,很好地抑制了边带波纹,增加了1064 nm反射率。通过对损伤阈值的分析发现,随着脉冲个数的增加,损伤阈值下降明显;但是在20个脉冲数后,损伤阈值（维持在22 J/cm2左右）几乎保持不变直到100个脉冲数。通过Leica显微镜对损伤形貌的观察,发现损伤诱因是薄膜表面的节瘤缺陷。通过扫描电镜（SEM）以及聚集离子束（FIB）对薄膜表面以及断面的观察,证实了薄膜的损伤起源于薄膜表面的节瘤缺陷。进一步研究得出,渐变折射率薄膜在基频光单脉冲下损伤主要是由初始节瘤缺陷引起的,在后续多脉冲激光辐照下初始节瘤缺陷引起烧蚀坑的面积扩大扫过薄膜上的其他节瘤缺陷,引起了其他节瘤缺陷的喷射使损伤加剧,造成损伤的累积效应。     

Surface electronic structure of the organic superconductor κ-(ET)2Cu(NCS)2 studied via photoemission microscopy

The surface electronic structure of cleaved single crystals of the organic superconductor κ-(ET)₂Cu(NCS)₂ has been studied using photoemission microscopy. Two types of cleaved surfaces were observed, displaying different valence band photoemission spectra and different spectral behavior near the Fermi level, E_F. In particular, spectra from one surface type display relatively broad spectral features in the valence band and finite spectral intensity at E_F, while spectra from the other surface type show well-defined valence band emission features and zero photoemission intensity at E_F. We propose that the spectral differences are due to a very short electron mean free path in this material, and our results are used to explain the differences between previously published photoemission spectra from this superconductor. We also report the results of an investigation of the electronic structure of defects in this material.     

Laser damage in silicon

Laser damage in silicon has been investigated using single crystals of p-type Si with thin wafers of 0.325 mm thickness being exposed to Nd³⁺ laser pulses. The laser was in a free generation mode, with wavelength 1.064 μm, and pulse duration time of 100 μs, with energy of 200 mJ pulse^-1. It was found that this energy caused visible damage at the sample surface, which is interesting topographically and from viewpoint of the theory of the interaction of laser light and solid dielectric matter.     

A replacement model for an additive damage model with restoration

A system existing in a random environment receives shocks at random points of time. Each shock causes a random amount of damage which accumulates over time. A breakdown can occur only upon the occurrence of a shock according to a known failure probability function. Upon failure the system is replaced by a new identical one with a given cost. When the system is replaced before failure, a smaller cost is incurred. Thus, there is an incentive to attempt to replace the system before failure. The damage process is controlled by means of a maintenance policy which causes the accumulated damage to decrease at a known restoration rate. We introduce sufficient conditions under which an optimal replacement policy which minimizes the total expected discounted cost is a control limit policy. The relationship between the undiscounted case and the discounted case is examined. Finally, an example is given illustrating computational procedures.