缺陷对HfO2薄膜的激光弱吸收与损伤阈值的影响

激光弱吸收是导致光学薄膜损伤的重要原因。在(5~43)mPa的氧分压下制备并测试了一组HfO2薄膜。实验发现,当氧分压小于20mPa时,薄膜弱吸收越大,损伤阈值越低;当氧分压大于20mPa时,薄膜的损伤阈值与弱吸收并不一一对应,具有较高弱吸收的薄膜可能同时具有较高的损伤阈值。建立了缺陷模型,采用有限元法模拟了缺陷对弱吸收测量和损伤阈值测量的影响,分析了缺陷尺寸、密度、吸收系数对弱吸收和损伤阈值的影响。研究结果显示,吸收系数高于薄膜1 000倍的缺陷可以降低薄膜的损伤阈值1 000倍,却并不影响薄膜的弱吸收。缺陷对HfO2薄膜的激光弱吸收与损伤阈值测试有完全不同的影响,是导致某些薄膜弱吸收与损伤阈值背离的原因。     

基于嵌入式系统的射频超导量子干涉仪控制系统

本文介绍了嵌入式系统在射频超导量子干涉仪控制系统中的应用，提出了嵌入式系统的整体方案，并对系统工作原理以及设计思想做了简要介绍．     

自发磁化的超导π环在电触发下的行为

运用Runge-Kutta四步积分法分析了一个双结π环电路在输入脉冲电流触发下自发磁化电流的翻转过程.发现在适当的参数条件下，输入周期性脉冲，π环环流会产生周期性翻转现象，由正到负和由负到正的翻转将产生不同的输出脉冲.以此可检验π环自发磁化电流的方向和电触发下的翻转现象. 关键词： π结 自发磁化 Runge-Kutta四步积分法     

HfO2/SiO2双色膜在1 064 nm和532 nm激光辐照下的损伤特性

 采用电子束蒸发的方式,制备了有氧化硅内保护层和没有氧化硅内保护层的1 064 nm高透过、532 nm高反射的HfO₂/SiO₂双色膜,测量了它们的光学性能以及在基频和倍频激光辐照下的抗损伤性能。结果表明:氧化硅内保护层提高了双色膜在基频光辐照下的损伤阈值,对双色膜在倍频光辐照下的损伤阈值无明显影响。通过观察薄膜的损伤形貌,分析破斑的深度信息结合驻波场分布,对两类双色膜在基频光和倍频光下的损伤机制做了初步探讨。分析表明:氧化硅内保护层提高了膜基界面的抗损伤性能,从而提高了双色膜在基频光下的损伤阈值。     

用于光束匀滑的连续相位板近场均匀性

 为降低高功率激光系统中连续相位板(CPP)后续元件的强激光损伤风险,综合考虑入射光强调制、干涉及衍射作用等多种影响因素,建立了CPP近场计算分析模型,模拟和分析了这些因素对CPP后的近场均匀性的影响。理论分析结果表明：CPP后的光束近场均匀性主要受入射光调制、CPP表面剩余反射率和衍射传输距离的影响;当入射光束质量较差时,CPP后的近场均匀性主要由入射光束质量决定,CPP剩余反射率和衍射传输距离对近场均匀性影响相对较小;但当光束质量比较理想时,干涉和衍射作用会破坏CPP的近场均匀性,衍射传输距离影响尤为突出。     

A new magneto-cardiogram study using a vector model with a virtual heart and the boundary element method

A cardiac vector model is presented and verified, and then the forward problem for cardiac magnetic fields and electric potential are discussed based on this model and the realistic human torso volume conductor model, including lungs. A torso-cardiac vector model is used for a 12-lead electrocardiographic (ECG) and magneto-cardiogram (MCG) simulation study by using the boundary element method (BEM). Also, we obtain the MCG wave picture using a compound four-channel HTc ·SQUID system in a magnetically shielded room. By comparing the simulated results and experimental results, we verify the cardiac vector model and then do a preliminary study of the forward problem of MCG and ECG. Therefore, the results show that the vector model is reasonable in cardiac electrophysiology.     

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。     

HfO_2/SiO_2薄膜的激光预处理作用研究北大核心CSCD

激光预处理是提高激光薄膜抗激光损伤阈值的重要手段。对电子束蒸发方式镀制的HfO2/SiO2反射膜采用大口径激光进行了辐照,并采用激光量热计测量了激光辐射前后的弱吸收值。采用聚焦离子束(FIB)技术分析了激光辐照后薄膜的损伤形态并探究了损伤原因,首次采用扫描电镜拍摄到了节瘤部分喷发时的形貌图,并对其进行了FIB分析,为进一步了解节瘤的损伤过程提供了依据。实验发现,激光辐照过后的激光薄膜弱吸收明显降低,激光预处理有效减少了引起薄膜吸收的缺陷,存在明显的清洗效应;在本实验采用的HfO2/SiO2反射膜中,激光预处理技术对于祛除位于基底上种子形成的节瘤是有效的,原因是激光辐射过后该节瘤进行了预喷发并不会对后续激光产生影响;而激光预处理技术对位于膜层中间的可能是镀膜过程中材料飞溅引起的缺陷是无效的,需要通过其他手段对该类节瘤进行祛除。     

Cardiac magnetic source imaging based on current multipole model

It is widely accepted that the heart current source can be reduced into a current multipole. By adopting three linear inverse methods, the cardiac magnetic imaging is achieved in this article based on the current multipole model expanded to the first order terms. This magnetic imaging is realized in a reconstruction plane in the centre of human heart, where the current dipole array is employed to represent realistic cardiac current distribution. The current multipole as testing source generates magnetic fields in the measuring plane, serving as inputs of cardiac magnetic inverse problem. In the heart-torso model constructed by boundary element method, the current multipole magnetic field distribution is compared with that in the homogeneous infinite space, and also with the single current dipole magnetic field distribution. Then the minimum-norm least-squares (MNLS) method, the optimal weighted pseudoinverse method (OWPIM), and the optimal constrained linear inverse method (OCLIM) are selected as the algorithms for inverse computation based on current multipole model innovatively, and the imaging effects of these three inverse methods are compared. Besides, two reconstructing parameters, residual and mean residual, are also discussed, and their trends under MNLS, OWPIM and OCLIM each as a function of SNR are obtained and compared.     

Magnetotransport properties of two-dimensional electron gas in AlGaN/AlN/GaN heterostructures

Magnetotransport measurements are carried out on the AlGaN/AlN/GaN in an SiC heterostructure, which demonstrates the existence of the high-quality two-dimensional electron gas (2DGE) at the AlN/GaN interface. While the carrier concentration reaches 1.32 × 10¹³ cm ^{- 2} and stays relatively unchanged with the decreasing temperature, the mobility of the 2DEG increases to 1.21 × 10⁴ cm²/(V·s) at 2 K. The Shubnikov—de Haas (SdH) oscillations are observed in a magnetic field as low as 2.5 T at 2 K. By the measurements and the analyses of the temperature-dependent SdH oscillations, the effective mass of the 2DEG is determined. The ratio of the transport lifetime to the quantum scattering time is 9 in our sample, indicating that small-angle scattering is predominant.