含有径向节点的拉盖尔-高斯光束产生涡旋高次谐波的特征

利用红外超快涡旋激光脉冲与气体介质相互作用可以产生携带轨道角动量的极紫外高次谐波。采用含有径向节点的拉盖尔-高斯（LG）光束作为驱动光,利用定量重散射模型计算单原子响应,通过求解谐波场在介质中传播的三维麦克斯韦方程以及在傍轴近似下的惠更斯积分,分别获得近场和远场高次谐波的强度和相位分布。结果表明:随着驱动光的径向节点数增加,高次谐波的强度分布呈现多环结构,相位分布上出现节点结构,强度分布的空间范围在近场减小,而在远场增大。相位匹配分析显示,短轨道和长轨道高次谐波的空间相干长度分布图对驱动激光的模式非常敏感,与高次谐波场在气体介质内的演化图像定性一致,解释了有径向节点的LG光束作用下产生的涡旋高次谐波的特征。     

静电场对强激光场中氢原子产生高次谐波的影响

利用分裂算符方法数值求解了真实氢原子在强激光场和静电场作用下的含时薛定谔方程,研究了静电场对强激光场中氢原子产生高次谐波的影响.研究表明,静电场加入后,奇次谐波的强度有所降低,并且谐波谱中出现偶次谐波和双平台结构.利用小波变换,观察了高次谐波在不同时刻的发射情况.借助于半经典理论,解释了在静电场作用下高次谐波发生变化的机制.     

A novel overlay process for imprint lithography using load release and alignment error pre-compensation method

As a low-cost and high-efficiency alternative to conventional photolithography, imprint lithography has been paid serious attention for it can realize the pattern transfer easily and repeatedly. Even so, there is still a long way to go before this technique can be used to manufacture ICs since the layer-to-layer alignment is a main obstacle. In this paper, the pattern distortion and position shift induced by loading force and friction force are investigated and an optimized process is proposed to realize high precision overlay, in which an optimal loading force and a load release and an alignment error pre-compensation (LRAEPC) method are adopted. The optimal loading force is acquired by comparing the variety trends of the residual layer and position shift with the loading force. Using the optimal loading force, transferred patterns with proper resist thickness and the minimal distortion are achieved. In LRAEPC method, load release is used to correct the pattern distortion and to alleviate the position shift. To avoid subsequent position adjustment in the fluid after load release, the pre-compensation alignment is performed before the mold is in contact with the wafer. This process does not locate correct alignment position and there is an alignment compensation value determined by the statistical data of alignment position shift after load release. Using this pre-compensation alignment method, the correct alignment can be obtained after load release.     

用于纳米劈裂技术的新型芯片及增强拉曼光谱实验

为了定量研究纳米颗粒的间距对拉曼(Raman)光谱强度的影响,研制了具有高稳定性的纳米劈裂芯片及装置。利用此芯片及装置,可以获得纳米金属桥断裂后自动形成的两针状纳米电极(纳米颗粒),并且能在pm级精度上操纵两纳米电极间的距离,以观察相应拉曼光谱强度的变化。在利用两纳米电极作为增强体的基础上引入了第3纳米电极,以观察其位置对拉曼光谱信号的影响。实验结果表明,光谱信号的强度强烈依赖于3纳米电极的相对位置,第3纳米电极的引入能进一步提高增强因子,为拉曼光谱增强机制的理论研究提供了重要参考数据。     

Manufacturing of laser diode modules: Integration and automation of laser diode-fiber alignment and RIN characterization

Laser diode-fiber alignment and relative intensity noise (RIN) characterization are two crucial steps to the manufacturing of fiber pigtailed laser diode modules. Integrating both steps into a single automatic process can increase yield, improve the throughput and reduce manufacturing cost. This work presents a novel scheme of the integrated laser-diode-to-fiber alignment and RIN testing automation for the manufacturing of Fabry-Perot (FP) laser diode module hosted in a low cost isolator-free coaxial-type package. It is demonstrated that the value of RIN is not only determined by the intrinsic spontaneous emission of the laser diode, but also strongly dependent on the fiber-laser alignment and pigtailing process. It is experimentally determined, for the first time, that regardless of the type of lensed fiber employed for fiber-laser coupling, and with or without the presence of angular misalignment, there is an optimal fiber-laser alignment location at which the RIN value reaches its minimum. Moreover, it is observed that both RIN minimization and laser power coupling maximization occur at the same fiber-laser alignment position.     

自适应聚焦下基于强度传输方程的相位恢复

基于强度传输方程的非干涉相位恢复方法是通过对强度图像求解方程来获取相位的一种途径。在图像采集过程中,对聚焦图像的选择是很重要的。但该过程通常是由主观方法来确定,从而导致聚焦定位不准确,进而影响相位恢复结果的精度。首先,提出了一种基于强度传输方程的自适应聚焦相位恢复方法;其次,使用边缘占空比对采集图像进行定位,在求解相位之后进行循环角谱传播,直到边缘占空比定位位置不变,即被认为是定位到了最佳聚焦位置;最后,再使用强度传输方程求解样本的相位。结果证明:该方法不仅提高了相位恢复的准确性而且减少了获取大量图像的次数。在模拟实验中,恢复相位与原始相位的相关系数达到0.9866,均方根误差为0.3050。在实际的微透镜阵列实验中,用所提出的相位恢复方法恢复出的微透镜高度与真实高度误差仅为5.7%,证明了在显微成像领域,所提算法可以定位到最优聚焦位置,有利于自动聚焦技术的发展,进而提高相位恢复的精度。     

基于衍射光栅的超精密定位技术研究

分析了一种百纳米级位移分辨率的双级衍射光栅测量系统, 建立了衍射叠栅(莫阿)信号与对应位移的数学模型, 并通过计算机仿真对叠栅信号的位移特性进行了研究。在此基础上设计了一套基于双级衍射光栅的精密定位装置, 利用两组衍射光栅, 取其透射零次激光叠栅信号的差信号为控制信号, 由微机控制实现高精度位置检测及精密自动定位。系统采用的差动光栅技术, 极大地提高了位置检测信号的灵敏度及定位精度。通过粗定位和精定位相结合的两段式复合定位, 可在高精度定位的同时, 缩短定位时间, 实现高速高精度定位。实验结果表明, 基于衍射光栅的精密定位装置可获得±0.5 μm的定位精度, 对精密加工工程领域具有重要的实用价值。     

Light‐Stimulatable Molecules/Nanoparticles Networks for Switchable Logical Functions and Reservoir Computing

The fabrication and electron transport properties of nanoparticles self‐assembled networks (NPSAN) of molecular switches (azobenzene derivatives) interconnected by Au nanoparticles are reported, and optically driven switchable logical operations associated to the light‐controlled switching of the molecules are demonstrated. The switching yield is up to 74%. It is also demonstrated that these NPSANs are prone to light‐stimulable reservoir computing. The complex nonlinearity of electron transport and dynamics in these highly connected and recurrent networks of molecular junctions exhibits rich high harmonics generation (HHG) required for reservoir computing approaches. Logical functions and HHG are controlled by the isomerization of the molecules upon light illumination. These results, without direct analogs in semiconductor devices, open new perspectives to molecular electronics in unconventional computing.     

干扰对齐的分集检测算法研究

为了优化干扰对齐的检测算法,在分析其信号空间特点的基础上,该文提出了分集检测算法。该算法把信号在信号空间中的投影作为检测向量,以达到提高接收信噪比的目的。仿真结果表明与现有算法相比,当干扰对齐条件严格满足时,分集检测算法有明显的增益,而且,分集度越高,增益越显著。     

一种基于正弦波磁光调制的空间大范围方位自动对准方法

针对基于正弦波磁光调制的方位对准系统存在方位失调角对准范围小的问题,在阐述了方位对准原理、分析磁光调制后混合信号成分的基础上,提出了一种空间大范围方位自动对准方法。通过磁光调制前后交流信号(AC)的相位对比得出了判断失调角正负的方法,利用方位对准系统中下仪器的初始架设位置和转动方式实现了初始光强的自主测量,在此基础上利用大角度范围内采集的磁光调制后的直流信号(DC)建立了粗略失调角的计算模型,并详述了具体实现方案,下仪器在粗略失调角信号的控制下逐渐转动至小角度范围内。之后,利用磁光调制后采集的交流信号实现了小角度范围内失调角的精确测量,两个模型紧密配合保证了空间大范围方位自动对准。仿真结果表明,提出的方法理论上可以实现-90°～90°范围内较高精度的自动对准,有效扩大了方位失调角的对准范围,解决了传统的方位对准范围小的问题。     

基于波前编码的大焦深弹载双色红外探测系统

波前编码技术通过在光学系统光瞳位置加入特殊的相位掩模板,对目标信号光波进行编码调制,并在图像处理端对该编码信号进行解码而恢复原图像,由于被编码调制后的波前对离焦等像差的不敏感度扩大了十数倍,能显著扩大光学系统焦深。因此,波前编码技术能在编码与解码之间解决恶劣力热条件或多色制导体制对弹载红外探测系统带来的离焦和对准误差。文中基于波前编码扩大焦深基本原理,对一长长双色红外光学系统进行了10倍焦深扩大的波前编码像差钝化设计。集成样机后,进行了波前编码成像实验。以小孔点靶编码像作为PSF解码10倍离焦位置处的十字靶和四条靶图像,十字靶和四条靶解码图像清晰可辨,证明波前编码技术对于系统像差或离焦像差的抑制是有效的。最后,对波前编码成像效果进行了分析:解码图像的水波纹是由于空间采样PSF不足导致的,可提取不同视场位置PSF,使用空间变化解码算法实现条纹消除;由于解码图像会在放大信号的同时放大噪声,因此,解码算法需要进一步研究噪声抑制算法,以期满足弹载高能量、高信噪比应用的要求。     

Nikon光刻机对准系统概述及模型分析

对准系统是光刻机中最精密复杂的部分,掌握对准原理是设计和使用光刻机的关键之一。阐述Nikon步进投影光刻机（Stepper）的对准机制,详细介绍目前应用于Nikon步进光刻机硅片对准的三种对准方式：LSA、FIA、LIA,比较它们的优缺点。并结合数学模型对影响Nikon对准模型信号强度进行分析,为提高对准精度提供了依据,对实际应用有一定的指导作用。     

Magnetic Fields as an Investigation Technique and Manipulation Tool for Phthalocyanine Molecular Aggregates

A polarized absorption spectroscopy (PAS) study of molecular aggregate solutions of phthalocyanine molecules in high magnetic fields is presented. We show that a magnetic field can induce macroscopic ordering of molecular aggregates (MAs), in a clean, non‐contact method, which is well suited for MA manipulation. We also demonstrate that magnetic‐field‐induced alignment in combination with PAS can be used to determine the MA size and the precise position of the absorption lines in concentrated solutions, as well as probe interaggregate interactions.     

A High Speed Autofocusing System for Micro System Applications

In this paper, we present a high speed autofocus system for micro system applications and design a look-up-table based autofocusing algorithm for applications when a target object is always visible, e.g., manufacturing parts with alignment fiducials. We perform an evaluation of 24 focus measures to verify that which focus measure is the best for the look-up-table based method. From the evaluation, we find that the Chebyshev moments-based focus measure (CHEB) is the most suitable. Furthermore, we also develop a look-up-table based autofocus system that uses CHEB as the focus measure. In training phase, we offline construct a table from training images of an object that are captured at several lens distances. Each entry of table consists of focus measure computed from image and lens distance. In working phase, given an input image, the algorithm first computes the focus measure and then finds the best match focus measure from the table and looks up the corresponding lens position for moving it into the in-focus position. Our algorithm can perform autofocusing within only 2 steps of lens moving. The experiment shows that the system can perform high speed autofocusing of micro objects.     

Novel high precision alignment technique for polarisation maintaining fibres using a frequency modulated tunable laser

A precision alignment technique for polarisation-maintaining, fibres is described using a frequency modulated tunable laser in combination with phase sensitive detection. The effect of residual intensity modulation is overcome by detecting the signal at twice the modulation frequency. An alignment accuracy of better than 0.2 degrees was achieved.<>     

精密定位中激光衍射信号的数值仿真

针对采用二维黑白光栅衍射的精密定位系统,对其衍射信号进行了分析和建模,并采用Gauss积分法对模型进行了仿真和实验验证,结果表明,经双光栅衍射后的摩尔信号变化具有稳定的周期性,其中零次摩尔信号在各级衍射光中光强最强,非常适合用于高精密定位。     

保偏光纤器件的对轴角度分析与测量

理论推导了保偏光纤(PMF)对轴角度、起偏器起偏角与相干域检测信号的关系,仿真分析表明,对轴误差越大,引起的偏振耦合越大.根据白光干涉原理,采用Michelson干涉仪光程补偿的方法,实验研究了偏振耦合强度与对轴角度之间的关系,并根据测量的耦合强度数据计算出对轴角度.     

空间光-光纤阵列耦合自动对准实验研究

为了使空间光-光纤耦合结构具有一定的抗抖动能力,采用自聚焦透镜和多模光纤耦合阵列结构结合模拟退火算法对光纤阵列实行2维控制,自动搜寻空间光-光纤耦合最佳视轴对准姿态。对光纤阵列和模拟退火算法进行了理论分析实验验证,取得了耦合效率变化的相关数据。结果表明,通过模拟退火算法可以实现空间光-光纤视轴对准,且光斑中心在耦合端面中心抖动小于2.5mm时,耦合功率波动小于35%,满足无线激光通信系统的要求。     

Near-optimal detection of geometric objects by fast multiscale methods

We construct detectors for "geometric" objects in noisy data. Examples include a detector for presence of a line segment of unknown length, position, and orientation in two-dimensional image data with additive white Gaussian noise. We focus on the following two issues. i) The optimal detection threshold-i.e., the signal strength below which no method of detection can be successful for large dataset size n. ii) The optimal computational complexity of a near-optimal detector, i.e., the complexity required to detect signals slightly exceeding the detection threshold. We describe a general approach to such problems which covers several classes of geometrically defined signals; for example, with one-dimensional data, signals having elevated mean on an interval, and, in d-dimensional data, signals with elevated mean on a rectangle, a ball, or an ellipsoid. In all these problems, we show that a naive or straightforward approach leads to detector thresholds and algorithms which are asymptotically far away from optimal. At the same time, a multiscale geometric analysis of these classes of objects allows us to derive asymptotically optimal detection thresholds and fast algorithms for near-optimal detectors.     

用大像元CMOS线阵光电探测器和插值法测量激光光斑中心位置

探讨了用大像元 (0 .8mm)CMOS线阵光电探测器确定激光光斑中心位置的插值方法 ,并对插值误差进行了理论分析和实验验证。采用线性插值可使测量分辨率提高 10倍以上。通过实测两种激光准直中光斑中心位置的漂移 ,验证了该探测器及插值方法的实用性。