超高强度飞秒脉冲的三次谐波转换

针对超高强度飞秒激光,对利用单块BBO晶体产生三倍频(THG)的过程进行了分析,比较了单块晶体中三阶非线性效应以及级联二阶非线性效应对三倍频转换效率的作用,讨论了入射基频光光强、晶体厚度、自相位调制(SPM)、交叉相位调制(XPM)、群速度失配、失谐角、方位角等因素对三倍频光转换效率、时间波形及光谱分布的影响,在此基础上,提出了提高三倍频转换效率的方法.研究结果表明:入射基频光强一定时,三倍频光的峰值光强、脉冲宽度(FWHM)随晶体厚度变化不明显.通过优化基频光入射角度,可提高单块BBO晶体三倍频光转换效率及峰值光强,并减小三倍频光脉冲宽度.此外,方位角的优化也可在一定程度上提高三倍频转换效率.     

高强度飞秒脉冲单块BBO晶体三倍频实验

针对脉冲宽度100 fs,带宽25 nm,能量6 mJ左右的超短脉冲基频光(经过透镜缩束后峰值光强为200~900 GW/cm2),采用单块厚度为1.5 mm的BBO晶体进行了三倍频实验研究。在入射基频光强度约300 GW/cm2时,得到的三倍频转换效率约0.8%。采用分步傅里叶变换及四阶龙格-库塔算法,对描述飞秒脉冲单块晶体三倍频的耦合波方程组进行了数值计算。研究结果表明,三倍频光主要是由三阶非线性效应产生的;基频光带宽较大是限制三倍频转换效率的主要因素之一;对基频光的入射角度及方位角进行优化,可较好地补偿非线性相位失配,提高单块晶体三倍频转换效率。     

高效短脉冲宽带倍频绿光实现方法

针对纳秒量级调Q宽频带光纤激光器,分别模拟了利用光栅角色散补偿(ASD),棱镜ASD以及晶体级联方法对倍频效率的影响。采用LBO晶体Ⅰ类相位匹配,通过数值求解高斯光束三波耦合方程,得到了入射基频光线宽、聚焦光斑位置、聚焦光斑大小以及晶体长度对倍频转换效率的影响,并对晶体参数进行优化。计算结果显示:直接倍频时,对于5 nm宽频带激光,倍频效率只有17%;采用光栅角色散补偿可以在大光谱范围内倍频效率达到70%以上;棱镜提供的补偿较小,但也能使倍频效率提高50%;三块晶体级联可以使倍频效率提高130%。     

高效宽带二倍频激光原理及实现方法

利用两块Ⅰ类KDP倍频晶体级联的方式,研究了时间相位调制宽带激光的二倍频特性.实验获得了二倍频转换效率与入射基频光功率密度的关系,在基频光功率密度为1.6 GW/cm2时,最大二倍频转换效率达70％,接近理论模拟的结果.实验结果表明,在高功率密度和低功率密度基频光条件下,倍频光光谱宽度约为入射基频光带宽的一半,与理论计...     

折返点匹配的宽带二倍频实验研究

在二次谐波转换中,基频光和倍频光的群速失配是限制转换带宽的主要因素。利用折返点匹配的宽带谐波转换技术能同时实现基频光和倍频光的相位匹配和群速匹配,理论计算表明在折返点匹配的情况下,倍频转换带宽将显著增加。分别利用厚度10 mm,氘含量12%的KD*P晶体和厚度12 mm的KDP晶体对中心波长为1053 nm,谱宽为31 nm,能量为620μJ的基频光进行折返点匹配二倍频和传统二倍频的对比实验,前者取得了22 nm的转换带宽,远大于后者7 nm的转换带宽。实验结果证实了理论计算的正确性,显示了折返点匹配宽带谐波转换技术的优越性。相应地,前者转换效率为25%,大于后者20%的转换效率,导致倍频转换效率较低的主要因素是入射基频光的光束质量和光谱质量较差。     

高强度三倍频实验研究

针对KDP晶体的TypeI+ TypeⅡ匹配方式的三倍频方案,采用理论模拟与实验研究相结合方式,从非线性耦合波方程组出发,编制了考虑衍射、离散、吸收和端面反射等物理因素的二维模拟计算程序.针对x、y方向均是六阶超高斯分布的入射基频光,功率密度在2～8 GW/cm2时,得到了TypeⅠ倍频晶体厚度11.8 mm、失谐角300 μrad,TypeⅡ混频晶体厚度9 mm、失谐角为0 μrad的优化参数,此时三倍频转换具有较大的动态范围和较高的效率. 在星光Ⅱ激光装置大厅建立了高强度三倍频实验研究平台,实验平台上基频光光束口径为Φ70 mm、功率密度为1～7 GW/cm2内可调、脉冲宽度约为0.8 ns.在实验平台上采用Φ100 mm能量卡计对基频光(1ω)、二倍频(2ω)和三倍频光(3ω)的能量进行测量,二、三倍频的外部转换效率可达60%以上;利用条纹相机对1ω光和3ω光的脉宽进行测量,脉宽变化基本为0.8 ns(1ω)和0.5 ns(3ω);采用512×512点阵的CCD对1ω光和3ω光的近场分布进行了对应测量,通过图像处理,得到描述光束质量的强度调制度和通量对比度值.基频光的远场发散角利用列阵相机进行监测,得到对应的1ω光光束发散角θ=0.3±0.06 mrad.在倍频晶体后5 m远处用哈特曼小孔阵列板测量基频光和三倍频光的波前分布,得其均方根(rms)分别为1.129 waves和0.425 waves.实验中,当入射基频光功率密度较高时,倍频晶体出现了明显的非线性自聚焦丝破坏现象.(OB11)     

脉冲形状对3次谐波转换的影响分析

为了使谐波转换系统保持高效稳定的3次谐波转换,采用数值模拟的方法,研究了基频光脉冲波形对3倍频转换效率的影响,并对高斯脉冲和平顶脉冲的不同谐波转换特点作了详细分析.当基频光为高斯脉冲时,在3GW/cm2的输入条件下最佳的2倍频转换效率为56.8%,低于理论预计的66.7%.进一步计算了不同功率密度下,最佳2倍频转换效率与超高斯脉冲阶数的关系.当考虑空间走离效应,基频光时间和空间均为平顶分布时,最佳的2倍频转换效率为62%;若基频光时间为平顶分布、空间分布为高斯分布时,最佳2倍频转换效率为51%,进一步地偏离66.7%.结果表明,当基频光脉冲形状偏离理想的平顶分布时,适当地降低2倍频转换效率,可提高3倍频转换效率.     

飞秒激光脉冲倍频特性的数值模拟

模拟了随着传播长度的增加,基频和倍频激光脉冲的时域波形和光谱特性的演变过程。通过引入走离长度和非线性长度,给出了走离效应、群速度色散和三阶非线性效应对飞秒脉冲倍频的影响。研究了飞秒脉冲倍频的波长调谐特性,发现40ps基频脉冲波长调谐带宽仅有2.8nm,而40fs基频脉冲的倍频波长调谐带宽高达42nm。这在周期极化倍频晶体工艺中有重要应用价值。     

脉冲形状对三次谐波转换的影响分析

本文研究了基频光脉冲波形对三倍频转换效率的影响,对高斯脉冲和平顶脉冲的不同谐波转换特点作了详细分析,研究结果表明,当基频光脉冲形状偏离理想的平顶分布时,适当地降低二倍频转换效率,可提高三倍频转换效率。当基频光为高斯脉冲时,在3GW/cm2的输入条件下最佳的二倍频转换效率为56.8％,低于理论预计的66.7％。进一步的,计算了不同功率密度下,最佳二倍频转换效率与超高斯脉冲阶数的关系。     

CsLiB6O10晶体的宽带三倍频模拟分析

为了研究高效的宽带三次谐波转换技术,采用了分步傅里叶变换和四阶龙格-库塔法对CsLiB6O10(CLBO)晶体的宽带三倍频过程进行了数值模拟,分析了单倍单混和单倍双混模式下三倍频转换效率随入射基频光强度、频谱带宽的变化关系,并与KDP晶体的宽带三倍频转换特性进行了对比.在强度为3GW/cm2的0阶超高斯脉冲入射下,得到单倍双混模式下三倍频转换效率达到60%时对应的频谱宽度为650GHz,这与利用KDP晶体在相同条件下获得的频谱宽度相比,提高了近250GHz.研究结果表明,在单倍双混模式下使用CLBO晶体作为频率转换的非线性晶体可以有效地提高宽带三倍频的转换效率.     

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.     

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.     

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.     

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.     

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.     

Teleportation of an arbitrary unknown N-qubit entangled state under the controlling of M controllers

A new quantum protocol to teleport an arbitrary unknown N-qubit entangled state from a sender to a fixed receiver under M controllers(M < N) is proposed. The quantum resources required are M non-maximally entangled Greenberger-Home-Zeilinger (GHZ) state and N-M non-maximally entangled Einstein-Podolsky-Rosen (EPR) pairs. The sender performs N generalized Bell-state measurements on the 2N particles. Controllers take M single-particle measurement along x-axis, and the receiver needs to introduce one auxiliary two-level particle to extract quantum information probabilistically with the fidelity unit if controllers cooperate with it.     

Diode-end-pumped Nd:YVO4/LBO lasers with 4.2W continuous-wave output at 457 nm

A continuous-wave (CW) 457 nm blue laser operating at the power of 4.2 W is demonstrated by using a fiber coupled laser diode module pumped Nd: YVO4 and using LBO as the intra-cavity SHG crystal With the optimization of laser cavity and crystal parameters, the laser operates at a very high efficiency. When the pumping power is about 31 W, the output at 457nm reaches 4.2 W, and the optical to optical conversion efficiency is about 13.5% accordingly. The stability of the out putpower is better than 1.2% for 8 h continuously working.     

Call for Papers

正Wireless Body-area Networks The last decade has witnessed the convergence of three giant worlds:electronics,computer science and telecommunications.The next decade should follow this convergence in most of our activities with the generalization of sensor networks.In particular with the progress in medicine,people live longer and the aging of population will push the development of wireless personal networks     

Call for Papers—Feature Topic,Vol.12,No.7,2015

正Information Centric Networking Information-Centric Networking(ICN) is an emerging direction in Future Internet architecture research,gaining significant tractions among academia and industry.Aiming to replace the conventional host-to-host communication model by a data-centric model,ICN treats data content as the first