硅相变过程中皮秒性质的研究

本文报道了裸硅、二氧化硅-硅、SOS等材料在0.53μm约30ps的脉冲激光作用下产生的相变过程中反射率及透射率的变化和与之相关的实验现象.这些结果直接证实了硅中能量转移、相变以及熔融态的过加热可在ps时间内出现.     

激光脉冲照射硅时若干物理量的计算

本文计算了由毫微秒和微微秒激光脉冲照射而在硅晶体中产生的晶格温度、载流子浓度和载流子温度的时间演变和空间分布,本文用PDECOL软件包计算一组关于晶格温度、载流子浓度、载流子温度和激光强度的偏微分方程组的数值解。计算表明,热载流子的能量弛豫时间应为1ps或小于1ps,计算的熔化阈值与发表的实验结果是一致的。     

有预脉冲条件的激光加热等离子体的效率

本文首先从理论上对强激光辐照下的等离子体密度线型进行计算,在这个基础上,仔细地分析了有预脉冲存在情况下的激光与等离子体相互作用效率,得到在预脉冲能量为主脉冲的30%、时间间隔为100ps时,等离子体对激光能量的最大吸收效率可达到与没有预脉冲情况下的9倍左右。     

纳秒/皮秒双束激光联合驱动双层靶的γ辐射特性

基于神光Ⅱ升级装置,研究了纳秒/皮秒双束激光联合驱动双层靶的伽马(γ)辐射特征。利用ns束激光与CH薄膜靶相互作用,产生大尺度近临界密度等离子体,然后将ps束激光作用在该等离子体上,产生高能电子,高能电子穿过2 mm厚的Au靶,通过轫致辐射产生γ射线。对不同方向的γ辐射能谱和靶室外的γ辐射剂量分布进行实验测量,发现γ辐射集中在激光前冲方向,具有较小的发散角,而且在该方向上高能段的γ辐射较强。这说明双层靶的设计可以提高ps束激光与等离子体的能量耦合效率,提高高能电子温度,增加高能电子数目,有利于高能段γ辐射在ps束激光的前冲方向集中。另外,在靶室外距离靶点1.25 m处测到的50 keV以上γ辐射的单发次最大剂量为277 μGy。本研究结果对γ辐射的防护和应用具有参考价值。     

紧聚焦条件下飞秒激光产生空气等离子体的动态演化特性

采用具有旋转对称性的三维空间电离模型,对紧聚焦条件下中心波长为800nm、脉冲宽度为50fs的激光脉冲产生的空气等离子体的时间和空间特性进行了数值模拟,揭示了整个等离子体区折射率的动态演化过程。计算结果表明:当激光脉冲开始聚焦时,靠近焦点前方的空气首先被电离,随后产生一个中心区域达到饱和、边缘具有很高折射率梯度的水滴状等离子区域;随着激光脉冲继续向焦点传播并越过焦点,等离子体区进一步向前延伸,直至在焦点前后形成一个近乎对称的双卵形结构;脉冲通过焦点区域后,空气等离子体强度沿传播方向逐渐减弱,直到最终完全消失;在10倍物镜聚焦下,脉冲能量为500μJ、脉冲宽度为50fs的激光脉冲产生的空气等离子体由产生到消失的整个过程约持续3ps。理论计算结果与30kPa低气压环境下的实验观测结果相吻合。     

一种进行激光等离子体通道实验的设计

利用一束激光产生等离子体通道,进而使点火激光能顺利到达高密度区是快点火理论中实现点火的一个重要过程。提出了一种利用神光Ⅱ的二路装置产生通道的设计。该设计将其中一路长脉冲激光(350 ps,1.053μm)辐照靶箔产生等离子体,用另一路短脉冲激光(1 ps,1.053μm)在上述预等离子体中打通道,并将后者的一部分激光经分离和四倍频(0.263μm)后作探针光,采用Normaski型偏振干涉系统对通道等离子体电子密度分布进行干涉诊断测量的实验研究设计。     

激光等离子体的分幅干涉测量

我们以二甲亚砜作为喇曼介质,在输入为250ps的1.064μm激光脉冲作用下,得到脉宽为50ps左右、波长629.8nm、能量大于200μJ的后向喇曼散射激光,将它作为诊断用的光探针。提出了一种利用偏振棱镜分束的双幅干涉仪。每次打靶能够得到两幅不同时间点的干涉图。用上述探针系统和干涉仪相配合,在单路激光辐照球靶的实验中,得到了激光等离子体相     

被动式探针光系统工程化改造研究

星光Ⅱ激光装置上建立的紫外探针光系统,用星光Ⅱ的子束作为抽运光源,通过倍频和受激喇曼散射,将波长为1054nm、脉宽约为800ps的激光转换成波长为308nm、脉宽约为60ps、能量为1mJ左右的紫外光,作为激光等离子体诊断的光源。原有探针光系统由于受系统结构不稳定及光束质量较差等因素的影响,不能稳定运行。为了提高系统的运行质量和稳定性,对原系统进行了工程化的改造。通过实验验证,探针光系统输出能量能够达到1mJ左右、脉宽约为30ps、均匀性较好、运行成功率大于90%,这一结论满足了激光等离子体诊断光源的要求。     

激光诱导铝合金等离子体的时间演化过程研究

为了深入研究激光诱导等离子体的物理特性,提高激光诱导击穿光谱(LIBS)技术的测量精度和可靠性,对激光诱导等离子体的时间演化过程进行了实验研究。采用ICCD相机对激光诱导铝合金等离子体进行快速成像,发现激光诱导铝合金等离子体的寿命大约为30μs,等离子体呈现明显的分层结构,并且不同区域的面积和温度在等离子体的时间演化过程中呈现不同的特征。通过玻尔兹曼斜线法和Stark展宽法计算了铝合金等离子体电子温度和电子数密度的时间演化规律。实验结果表明,等离子体的电子激发温度在6000K~9000K之间,且前3μs下降较快;等离子体电子数密度为1017 cm-3量级,并随ICCD探测延迟时间缓慢降低。等离子体电子温度和电子数密度的时间演化规律与ICCD相机快速成像结果一致。     

关键参数对空气中激光引致热核特性的影响规律研究

针对纳秒脉冲激光能量在空气中沉积的等离子体热核演化问题,利用两种不同分辨率的高速相机,搭建了高分辨率的纹影系统。所获得的纹影实验结果很好地展示了激光能量沉积初始时刻的演化过程,并研究了激光能量大小和透镜焦距这两个关键参数对激光引致等离子体热核演化过程的影响规律。实验结果表明激光沉积能量越大,等离子体热核的尺寸越大,但是可能存在激光能量沉积的饱和现象。另外,激光能量越高、透镜的焦距越短,激光能量沉积之后环境冷空气穿透热核的时间就越晚,意味着等离子体热核维持稳定的高温低密度气团的时间越长,这可以为激光致等离子体主动流动控制的相关研究提供充足的反应时间。     

Resolution Enhancement Technology:Integrated Process Solutions using OPC

DUV lithography, using the 248 nm wavelength, is a viable manufacturing option for devices with features at 130 nm and less. Given the low kl value of the lithography, integrated process development is a necessary method for achieving acceptable process latitude. The application of assist features for rule based OPC requires the simultaneous optimization of the mask, illumination optics and the resist.Described in this paper are the details involved in optimizing each of these aspects for line and space imaging.A reference pitch is first chosen to determine how the optics will be set. The ideal sigma setting is determined by a simple geometrically derived expression. The inner and outer machine settings are determined, in turn,with the simulation of a figure of merit. The maximum value of the response surface of this FOM occurs at the optimal sigma settings. Experimental confirmation of this is shown in the paper.Assist features are used to modify the aerial image of the more isolated images on the mask. The effect that the diffraction of the scattering bars (SBs) has on the image intensity distribution is explained. Rules for determining the size and placement of SBs are also given.Resist is optimized for use with off-axis illumination and assist features. A general explanation of the material' s effect is discussed along with the affect on the through-pitch bias. The paper culminates with the showing of the lithographic results from the fully optimized system.     

Cost-effective test solutions for smart card and other integrated flash applications

From its emergence in the late 1980s as a lower cost alternative to early EEPROM technologies, flash memory has evolved to higher densities and speedsand rapidly growing acceptance in mobile applications.In the process, flash memory devices have placed increased test requirements on manufacturers. Today, as flash device test grows in importance in China, manufacturers face growing pressure for reduced cost-oftest, increased throughput and greater return on investment for test equipment. At the same time, the move to integrated flash packages for contactless smart card applications adds a significant further challenge to manufacturers seeking rapid, low-cost test.     

An improved parallel thinning algorithm with two subiterations

The parallel thinning algorithm with two subiterations is improved in this paper. By analyzing the notions of connected components and passes, a conclusion is drawn that the number of passes and the number of eight-connected components are equal. Then the expression of the number of eight-connected components is obtained which replaces the old one in the algorithm. And a reserving condition is proposed by experiments, which alleviates the excess deletion where a diagonal line and a beeline intersect. The experimental results demonstrate that the thinned curve is almost located in the middle of the original curve connectivelv with single pixel width and the processing speed is high.     

Theoretical analysis of the relationship between the Brillouin gain coefficient and the strain in the optical-fiber sensors

The relation between the power of the Brillouin signal and the strain is one of the bases of the distributed fiber sensors of temperature and strain. The coefficient of the Bfillouin gain can be changed by the temperature and the strain that will affect the power of the Brillouin scattering. The relation between the change of the Brillouin gain coefficient and the strain is thought to be linear by many researchers. However, it is not always linear based on the theoretical analysis and numerical simulation. Therefore, errors will be caused if the relation between the change of the Brillouin gain coefficient and the strain is regarded as to be linear approximately for measuring the temperature and the strain. For this reason, the influence of the parameters on the Brillouin gain coefficient is proposed through theoretical analysis and numerical simulation.     

Novel fiber-optical interferometer with miniaturized probe for in-hole measurements

Today, micro-system technology and the development of new MEMS （Micro-Electro-Mechanical Systems） are emerging rapidly. In order for this development to become a success in the long run, measurement systems have to ensure product quality. Most often, MEMS have to be tested by means of functionality or destructive tests. One reason for this is that there are no suitable systems or sensing probes available which can be used for the measurement of quasi inaccessible features like small holes or cavities. We present a measurement system that could be used for these kinds of measurements. The system combines a fiber optical, miniaturized sensing probe with low-coherence interferometry, so that absolute distance measurements with nanometer accuracy are possible.     

Development of the readout system for waveguide multilayer optical card

Waveguide multilayer optical card （WMOC） is a novel storage device of three-dimensional optical information. An advanced readout system fitting for the WMOC is introduced in this paper. The hardware mainly consists of the light source for reading, WMOC, motorized stages addressing unit, microscope imaging unit, CCD detecting unit and PC controlling ＆ processing unit. The movement of the precision motorized stage is controlled by the computer through Visual Basic （VB） language in software. A control panel is also designed to get the layer address and the page address through which the position of the motorized stages can be changed. The WMOC readout system is easy to manage and the readout result is directly displayed on computer monitor.     

Study of waveguide coupling efficiency in hybrid silicon lasers

This paper presents a new method to increase the waveguide coupling efficiency in hybrid silicon lasers. We find that the propagation constant of the InGaAsP emitting layer can be equal to that of the Si resonant layer through improving the design size of the InP waveguide. The coupling power achieves 42% of the total power in the hybrid lasers when the thickness of the bonding layer is 100 nm. Our result is very close to 50% of the total power reported by Intel when the thickness of the thin bonding layer is less than 5 nm. Therefore, our invariable coupling power technique is simpler than Intel＇s.     

A method for calculating the center position of collimated light

It is a key problem to accurately calculate beam spots＇ center of measuring the warp by using a collimated laser. A new method, named double geometrical center method （DGCM）, is put forward for the first time. In this method, a plane wave perpendicularly irradiates an aperture stop, and a charge couple device （CCD） is employed to receive the diffraction-beam spots, then the geometrical centers of the fast and the second diffraction-beam spots are calculated respectively, and their mean value is regarded as the center of datum beam. In face of such adverse instances as laser intension distributing defectively, part of the image being saturated, this method can still work well. What＇s more, this method can detect whether an unacceptable error exits in the courses of image receiving, processing and calculating. The experimental results indicate the precision of this method is high.     

Collinear phase-matching study of terahertz-wave generation via difference frequency mixed in GaAs and Inp

The collinearly phase-matching condition of terahertz-wave generation via difference frequency mixed in GaAs and InP is theoretically studied. In collinear phase-matching, the optimum phase-matching wave hands of these two crystals are calculated. The optimum phase-matching wave bands in GaAs and lnP are 0.95-1.38μm and 0.7-0.96μm respectively. The influence of the wavelength choice of the pump wave on the coherent length in THz-wave tuning is also discussed. The influence of the temperature alteration on the phase-matching and the temperature tuning properties in GaAs crystal are calculated and analyzed. It can serve for the following experiments as a theoretical evidence and a reference as well.     

Effects of the alloy compositions on the phonon-polaritons in ternary mixed crystals

Composition dependence of bulk and surface phonon-polaritons in ternary mixed crystals are studied in the framework of the modified random-element-isodisplacement model and the Bom-Huang approximation. The numerical results for Several Ⅱ - Ⅵ and Ⅲ- Ⅴ compound systems are performed, and the polariton frequencies as functions of the compositions for ternary mixed crystals AlxGa1-xAs, GaPxAS1-x, ZnSxSe1-x, GaAsxSb1-x, GaxIn1-xP, and ZnxCd1-xS as examples are given and discussed. The results show that the dependence of the energies of two branches of bulk phonon-polaritons which have phonon-like characteristics, and surface phonon-polaritons on the compositions of ternary mixed crystals are nonlinear and different from those of the corresponding binary systems.