激光脉冲波形对液体中热膨胀机制致声特性的影响

首先阐述了激光与液体媒质作用通过热膨胀机制激发平面光声源的理论;分别针对激光脉冲为正弦波形、三角波形和高斯波形的情况,推导了激光脉冲分别在约束界面和自由界面下产生声脉冲的解析解,然后通过仿真得到了激发声波的光声脉冲剖面和时空分布图;并对比分析了正弦波形、三角波形和高斯波形的激光脉冲分别在约束边界和自由边界下激发声波的峰值声压、光声转换效率和波形等特性.     

激光打孔脉冲波形探讨

研究了打孔激光脉冲与材料的相互作用，提出一种新的深孔加工激光脉冲波形，更符合打孔过程向加工区输入能量的规律性，比常规波形脉冲更有利于打孔加工。     

机载激光波束扫描回波脉冲特征分析

本文介绍了脉冲激光束远区场的时空分布，导出了机载脉冲激光对地面扫描探测时回波脉冲的时域表达关系，通过数值计算得到了回波脉冲波形及其有关参数随扫描倾角的变化规律，结果表明不同波束倾角时回波脉冲特征发生了明显的变化。     

有限束宽下超高斯光束经光栅对压缩的研究

利用有限束宽下入射脉冲通过光栅对压缩的理论模型,从脉冲光束的傅里叶角谱入手,分析了脉冲超高斯光束单次及两次通过光栅对时的变换特性,以及高阶色散对脉冲压缩的影响。结果表明,脉冲超高斯光束单次通过光栅对压缩器时,横向谱移动使得出射光束产生时间相关的空间移动而两次通过压缩器时则会消除此种影响。高阶色散不仅影响输出脉冲的时间特性同时还影响其空间特性,导致输出脉冲波形扭曲,产生时空畸变。     

飞秒脉冲时空变换整形技术

飞秒激光脉冲通过时空变换技术将时域信息变换到空域,通过空域的处理再返回到时域,是实现飞秒激光脉冲整形、测量和控制的一项重要技术。在应用方面,可产生各种所需要的波形．已广泛应用在飞秒化学、信号处理、安全通信、生物学和医学成像等方面。介绍了飞秒时空变换脉冲整形的几种方法。     

自陡效应对飞秒脉冲光束自聚焦特性的影响

为了研究在非线性正常色散介质中,自陡效应对高强度飞秒脉冲光束自聚焦特性的影响,同时考虑色散、时空聚焦和克尔效应。基于(3+1)维的修正非线性薛定谔方程,采用对称分步傅里叶数值计算方法,分不考虑自陡效应即只有色散、时空聚焦及克尔效应和考虑自陡效应两种情况,对90fs超短脉冲光束的自聚焦特性进行了数值仿真。结果表明,色散、时空聚焦和克尔效应的共同作用会使脉冲分裂成丝,能量减少,脉冲展宽,时空聚焦和色散的相关性使脉冲产生了另一延迟,延迟和传输距离及色散成正比;而自陡效应则可以明显降低脉冲峰值强度,减弱非线性的影响,抑制脉冲自聚焦,使时间波形分裂更小,对脉冲延迟量影响较小。     

超宽带脉冲信号波形失真仿真与分析

超宽带无线信道的频率依赖特性直接影响到超宽带接收机的设计和以脉冲波形为基础的多址技术。本文针对频率依赖特性对超宽带脉冲信号波形产生的影响,分别从相位谱和幅度谱两个方面分析超宽带脉冲信号的相位失真和幅频失真特性,建立了描述脉冲波形失真特性的数学模型。使用该模型对高斯二阶导数脉冲信号的波形失真进行仿真分析,得到了只发生相位响应失真、只发生幅度响应失真、以及同时发生相位—幅度响应失真的脉冲波形。     

UWB脉冲的特征分析

介绍了超宽带脉冲无线电对脉冲波形的要求及FCC对UWB的频谱规划。详细分析了影响UWB脉冲波形及其谱形状的因素,分别给出了Rayleigh脉冲在不同脉冲形状参数α与不同求导阶数n时的时域波形及其频谱密度PSD,并研究了α与n对峰值频率及带宽的影响。分析结果表明,可通过仔细选择α与n来设计满足FCC频谱规划的脉冲,这对超宽带脉冲无线电中波形的选择具有指导性意义。     

强激光辐照半导体材料的温升及热应力损伤的理论研究

分别采用数值方法与解析方法 ,研究了连续波激光辐照半导体材料时产生的温升及热应力 .讨论了不同激光参数 强度、波形、波长及脉冲持续时间 与温度及热应力之间的关系 ,以及造成半导体材料热应力损伤的激光阈值强度 .     

跳时序列调制超宽带正交Hermite脉冲串雷达信号分析

超宽带正交Hermite脉冲是一类非常适合表征超宽带(UWB)穿墙探测雷达工作波形的脉冲,具有设计灵活、频谱利用率高、实现简单、波形存在解析表示方便理论分析等特点。该文从定义出发推导了跳时调制超宽带(TM-UWB)Hermite脉冲串波形的模糊函数解析表达式,仿真分析了模糊特性与跳时序列的自相关特性、序列周期以及与Hermite脉冲平均重复时间间隔,脉冲的阶数和时间尺度因子的关系,并探讨了在穿墙探测环境下该波形作用的旁瓣抑制和杂波抑制等关键技术。     

Protonation effect on the nonlinear absorption, nonlinear refraction and optical limiting properties of tetraphenylporphyrin

Nonlinear optical properties of tetraphenylporphyrin (H2TPP) and protonated tetraphenylporphyrin (H4TPP2+) in toluene were investigated by Z-scan technique using a nanosecond laser with 5 ns pulse at 532 nm. Results show that H4TPP2+ exhibits weaker nonlinear refraction but enhanced reverse saturable absorption (RSA) and optical limiting performance in comparison with pristine H2TPP. Since no nonlinear scattering is observed in H4TPP2+ under low input fluence, and H4TPP2+ exhibits weaker nonlinear scattering signals than H2TPP under high input fluence, the enhancement of RSA and optical limiting performance can be attributed to the larger ratio of excited state absorption cross-section to that of the ground state of H4TPP2+. H4TPP2+ also exhibits superior optical limiting performance, even better than the benchmark RSA material C60.     

飞秒化学研究进展

飞秒超快激光技术为物理、化学、生物学和材料等领域提供了一种新颖的工具,使研究人员可以研究其中发生的趟快过程,对当今的高科技和相应产业,如超怏光通信、新型有机无机材料、分子牛物学、基因工程等的研究和发展也具有重要意义.介绍了飞秒化学的最新进展,包括优化整形脉冲对化学反应的控制、飞秒位相相干二维光谱、晶格振动波的时空相干控制等.     

有机材料ZnTBP/CA/PhR体系的反饱和吸收特性研究

报道了有机材料ＺｎＴＢＰ／ＣＡ／ＰｈＲ对激光的反饱和吸收特性。理论分析从该材料特有的五能级结构出发，指出三重态的第一激发态在反饱和吸收过程中的重要作用，并用两束光同时照射样品的实验方法进行了验证。该材料的反饱和吸收效应可在功率不太高的连续光下操作     

Propagation of a radio pulse in isotropic plasma

The problem of propagation of a radio pulse in isotropic collisional cold plasma is solved. The solution analytically describes the spatiotemporal evolution of the characteristics of a radio pulse with an envelope of a rather general form. Explicit expressions are obtained for the velocity of radio-pulse propagation in isotropic plasma.     

飞秒激光诱发硅PIN光电二极管饱和特性的实验研究

实验研究了不同脉冲能量的飞秒激光诱发硅PIN光电二极管瞬态响应信号的特性。发现了探测器响应瞬态响应信号相继出现了三个明显的相位,深入讨论了飞秒激光诱发的高注入载流子在瞬态响应信号演化过程中所起的作用。结果表明,高注入载流子产生的空间电荷屏蔽效应是导致瞬态响应信号呈现三个相位的主要因素,它导致瞬态响应信号的持续时间主要取决于载流子双极扩散的速度。增加飞秒激光的脉冲能量会进一步延长探测器瞬态响应信号的持续时间。因此,飞秒激光会削弱探测器的工作性能,尤其是在高速信号探测中的工作性能。     

Investigations on the nonlinear optical properties of glycinium oxalate single crystals

Single crystals of glycinium oxalate (GLO) are grown by solution growth technique. The Z scan technique is used to elucidate the third order nonlinearity in the material. The results indicate that the compound exhibits reverse saturable absorption (RSA) and self-defocusing performance. The second harmonic generation (SHG) efficiency of the crystal evaluated by Kurtz and Perry technique is compared with that of the standard KDP crystal. Attempt is made to correlate the SHG efficiency with the crystalline perfection in the material.     

智能卡RSA密钥生成的VLSI实现

目前，智能卡中的RSA密钥生成通常由软件实现，速度较慢。文章给出了一种RSA密钥生成的VLSI实现方案，在RSA协处理器基础上增加若干运算单元，来完成RSA密钥生成和加解密操作。采用这种方式，密钥生成速度快，而且面积增加不多，适合于智能卡应用。     

Origin of the radio frequency pulse artifact in simultaneous EEG-fMRI recording: rectification at the carbon-metal interface

Simultaneous electroencephalograph-functional magnetic resonance imaging (EEG-fMRI) recording has become an important tool for investigating spatiotemporal properties of brain events, such as epilepsy, evoked brain responses, and changes in brain rhythms. Reduction of noise in EEG signals during fMRI recording is crucial for acquiring high-quality EEG-fMRI data. The main source of the noise includes the gradient artifact, the radio frequency (RF) pulse artifact, and the cardiac pulse artifact. Since the RF pulse artifact is relatively small in amplitude, little attention has been paid to this artifact, and its origin is not well understood. However, the amplitude of the RF pulse artifact fluctuates randomly even if a very high EEG sampling rate is used, making it more salient than the gradient artifact after postprocessing for noise removal. In this paper, we investigate the cause of the RF pulse artifact in EEG systems that use carbon wires.     

RSA密码算法的可重构设计与实现

本文对RSA密码算法的实现和可重构性进行了分析,在对模幂模块和模乘模块进行了可重构设计的基础上,提出一种可重构RSA硬件架构,使其能够适配256bit、512bit、1024bit、2048bit四种不同密钥长度的应用。RSA可重构设计在FPGA上进行了实现与测试,结果表明,工作在200MHz时钟时,2048bit密钥长度RSA在最坏情况下数据吞吐量可达46kb／s,能够满足高性能的信息安全系统对RSA算法的加密速度要求。     

ACO-based routing and spectrum allocation in flexible bandwidth networks

Optical networks with flexible bandwidth provisioning are a very promising networking architecture. It enables efficient resource utilization and supports heterogeneous bandwidth demands. In this paper, we focus on the dynamic routing and spectrum allocation (RSA) problem which emerges in such networks and propose a novel dynamic RSA algorithm by means of ant colony optimization (ACO). In our proposed algorithm, ants are launched to modify the routing table according to the length and the spectrum fragmentation information along the path. A simulation study is performed considering five algorithms in terms of blocking probability: WDM-based RWA approach, KSP-based RSA approach, Slot-based RSA algorithm, and our proposed ACO-based RSA approach. We then compare the deterioration degree of blocking probability by adding more types of line rate. Simulation results indicate that our proposed ACO-based RSA approach achieves lower blocking probability, complexity, and higher adaptability to more line rates mixture.