激光产生等离子体的研究

强激光（≈１０＾８－１０＾９Ｗ．ｃｍ＾－＾２）轰击固体靶产生等离子体，用４ｋＶ电势引出，得到最高总束流峰值为４．５ｍＡ，观察到离子最高电荷态为Ｃ＾３＾＋，Ａｌ＾３＾＋，Ｃｕ＾４＾＋，Ｔａ＾５＾＋，Ｐｂ＾４＾＋。另外，还详细研究了激光能数对等离子体的影响及激光等离子体的损失。     

激光对宽能域碳离子在双组份等离子体中阻止本领的影响

在线性化伏拉索夫-泊松模型基础上研究了激光辐照下碳离子在双组份等离子体中的阻止本领,重点讨论了不同激光振幅、激光频率、激光角度、等离子体密度和等离子体电子温度对阻止本领的影响。研究结果表明,在全域范围内,激光对阻止本领的影响都非常明显。在低能区域（入射速度为等离子体电子热速度的0～0.1倍）,碳离子的阻止本领主要来自于等离子体中离子的贡献,特别是在入射速度约为等离子体离子热速度时,阻止本领出现了第一个峰值;在中高能区域（入射速度大于0.1倍的等离子体电子热速度）,碳离子的能量损失主要来自于等离子体中电子的贡献,特别是在入射速度约为等离子体电子热速度的1.5倍时,阻止本领出现了第二个峰值。碳离子在等离子体中阻止本领的这种双峰结构体现了不同能量区域等离子体中离子和电子对阻止本领的贡献。另一方面,激光强度或激光频率的增加削弱了阻止本领,阻止本领会随着等离子体密度的增加或电子温度的降低而增强,特别是由于离子引起的低能峰与电子引起的高能峰相比阻止本领的增强更明显。     

阴阳极等离子体运动对强箍缩离子束二极管束流特性的影响

 主要研究了阴阳极等离子体运动对“闪光二号”加速器强箍缩离子束二极管束流特性的影响。给出了考虑阴阳极产生的等离子体运动对二极管间隙影响的Child-langmuir流、弱聚焦流、强聚焦流和饱和顺位流4个阶段的离子流和二极管总束流修正公式，利用这些修正公式计算的二极管总束流和离子束流强度与实测结果符合很好，在此基础上分析了提高离子束流强度和效率的方法，通过调整加速器参数，实验得到了峰值能量约500 keV，峰值电流约160 kA的高功率离子束。     

交叉传播激光脉冲与等离子体相互作用产生的等离子体密度光栅

理论上研究了两束交叉传播的激光束与等离子体相互作用产生的电子和离子密度调制. 用一维粒子模拟程序(particle-in-cell,PIC)研究了两束激光脉冲产生的干涉场激发的等离子体布拉格光栅. 研究表明等离子体初始密度、脉冲强度和宽度共同影响等离子体布拉格光栅的演化. 光栅的密度峰值可以达到初始等离子体密度的8倍以上,并且可以维持几皮秒的时间. 等离子体布拉格光栅可以囚禁由受激拉曼散射形成的电磁孤子,从而形成准稳态的孤子结构,很大程度上降低了形成电磁孤子所要求的激光脉冲强度. 关键词： 等离子体布拉格光栅 电磁孤子 交叉传播激光束 粒子模拟     

等离子体屏蔽效应对离子取出时间影响的实验研究

离子取出时间是原子法激光同位素分离（ＡＶＬＩＳ）过程中决定离子取出效率的关键参数之一，它主要受着等离子体屏蔽效应的影响。文中报告了这方面的实验研究结果。在阐述了等离子体屏蔽效应及存在条件的基础上，通过进行静电场（平行平板电场）收集铯（Ｃｓ）等离子体中铯离子的实验，发现在１０~９－１０~（１１）ｍ~（－３）等离子体密度范围内，离子取出时间与等离子体密度、收集场电压均是几何关系，即。     

核物理与等离子体物理学科研究进展

1 理论物理 1．1 等离子体物理 深入开展了激光等离子体相互作用理论研究。为了模拟和研究激光与大尺度黑腔等离子体相互作用问题，分析了激光入射场、散射波场和离子声波的传播的耦合关系，考虑动力学效应，提出了描述自聚焦、受激散射非线性演化的耦合模型，完成流体程序的物理方案；研究了SRS时空演化机制，发现一些新物理现象；对超强激光与超高密度等离子体作用问题进行模拟，研究了高能电子、单能离子产生的新特征。     

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应用电子和多光子集团非弹性碰撞模型和冷等离子体模型，研究了飞秒强激光与线性等离子体发生多光子非线性Compton散射时，散射激光与入射激光形成的飞秒耦合激光场对线性等离子体层中光场和电子密度分布的影响。研究发现，在耦合激光的有质动力作用下，电子密度分布和离子密度分布比Compton散射前的偏离更加严重，电子密度的变化比离子密度的变化更快，产生的静电场更强。即使耦合激光场非常弱，电子的运动仍表现出相对论效应，仍有静电场存在。     

飞秒和纳秒脉冲作用下等离子体X射线辐射特性

对飞秒和纳秒激光作用下的Ａｌ和Ｃｕ等离子体的Ｘ射线辐射进行了测量，分析和比较。实验结果表明在飞秒激光脉冲下等离子体Ｘ射线峰值向短波方向移动。     

强激光与稠密等离子体作用引起的冲击波加速离子的研究

用二维PIC（Particle-in-Cell）程序模拟研究了强激光与稠密等离子体靶作用产生的无碰撞静电冲击波的结构和这种冲击波对离子的加速过程,研究发现由于冲击波前沿附近的双极电场的作用,具有一定初速度的离子能被该双极场俘获并获得加速,最终能够被加速到两倍冲击波速度.冲击波加速可以得到准单能的离子能谱,叠加在通过鞘层加速机理产生的宽度离子能谱上.还对不同激光强度和不同等离子体密度情况下形成的冲击波进行了比较.研究表明,强度相对较低的激光在高密度等离子体中可以产生以一定速度传播的静电孤波结构,后者只能加速 关键词： 强激光 稠密等离子体 无碰撞静电冲击波 离子加速     

激光等离子体稳相加速机制研究

现有激光等离子体加速机制中纵向电场对离子的有效加速长度很短(微米量级),且束流能散大,得到的离子能量较低.当采用圆偏振激光和固体靶相互作用时,如果激光的归一化光强矢量α与靶的电子面密度no/nC D/kL相当时,则存在一种稳相加速机制.此时激光和等离子相瓦作用产生的静电场不仅可以用于加速离子,而且还可以在纵向对离子进行聚束,从而可以有效地降低束流能散.数值模拟结果表明,利用激光加速可以得到能散小于5%的单能离子束,这对激光加速器走向实际应用有着重要意义.     

Low energy ion beams by laser interaction

We developed an ion accelerator with a double accelerating gap system supplied by two power generators of different polarity. The ions were generated by laser ion source technique. The laser plasma induced by an excimer KrF laser, freely expanded before the action of accelerating fields. After the first gap action, the ions were again accelerated by a second gap. The total acceleration can imprint a maximum ion energy up to 160 keV per charge state. We analysed the extracted charge from a Cu target as a function of the accelerating voltage at laser energy of 9, 11 and 17 mJ deposited on a spot of 0.005 cm². The peak of current density was 3.9 and 5.3 mA for the lower and medium laser energy at 60 kV. At the highest laser energy, the maximum output current was 11.7 mA with an accelerating voltage of 50 kV. The maximum ion dose was estimated to be 10¹² ions/cm². Under the condition of 60 kV accelerating voltage and 5.3 mA output current the normalized emittance of the beam measured by pepper pot method was 0.22 π mm mrad.     

Optoelectronic resonant cavity technology based on inversion channel devices

In this paper the implementation of the inversion channel technology in a vertical cavity configuration is demonstrated. It is shown that by using a universal processing sequence a bistable surface emitting laser, a resonant cavity detector and a hetero-structure field effect transistor (H FET) can all be realized from a single epitaxial growth. The surface emitting double heterostructure opto-electronic switch (DOES) laser exhibits a pulsed threshold current of 10 mA for a 14 m diameter device. The resonant cavity detector achieved a peak responsivity of 0.6 AW^–1 in the H FET mode and 19 AW^–1 when operated in phototransistor mode. The H FET had a peak transconductance of 40 mS mm^–1 and a peak source to drain current density of 120 mA mm^–1.     

基于PSpice的半导体激光高频调制系统设计

为了实现高频率的调制激光输出,设计了一种驱动系统由信号放大、电流调制、过流保护和具有慢启动功能的直流偏置电路高度集成的半导体激光高频调制系统。此系统采用了结构简单的直接调制方式,运用线性调频的高频信号去控制半导体激光器发射激光的强度,从而实现高频调制。在运用OrCAD/PSpice对高频调制驱动系统进行模拟仿真的基础上,最终研制出的半导体激光高频调制系统实现了频率为40.02 MHz、直流偏置为493.326 mA、正弦波调制电流峰峰值为850 mA的高频调制输出,调制激光平均功率为300 mW。     

激光等离子体在螺线管发散磁场中的特性研究

激光烧蚀等离子体(LAP)可用作粒子加速器和离子注入器中使用的离子源。相较于其它离子源,激光离子源在流强上具有优势,但由于产生的离子束脉冲时间短,限制了其在加速器中的广泛应用。实验中通过对激光等离子体扩散区域引入螺线管磁场进行约束,实现了对激光等离子体脉冲时间结构的调制。为了研究螺线管磁场对LAP的影响,实验使用了不同的激光能量(1~8 J)来生产具有不同初始条件的激光等离子体,并应用了不同的磁场强度来约束激光等离子体。在螺线管边缘场,通过可移动的法拉第筒(FC)对激光等离子体的横向分布进行测量。对于不同初始状态的等离子体,随着磁场的增加,其离子脉冲的主要参数(脉冲总电荷量、峰值流强、脉宽)均呈现先上升后逐渐饱和的变化趋势。另外,在没有磁场的条件下,在所测量位置处,等离子体的横向呈均匀分布;而在磁场约束的条件下,等离子体明显向轴线聚集。以上实验结果对进一步了解磁约束激光等离子体的特性具有重要意义。     

A grating-coupled external cavity InAs/InP quantum dot laser with 85-nm tuning range

The optical performance of a grating-coupled external Continuous tuning from 1391 nm to 1468 nm is realized at cavity laser based on InAs/InP quantum dots is investigated. an injection current of 1900 mA. With the injection current increasing to 2300 mA, the tuning is blue shifted to some extent to the range from 1383 nm to 1461 nm. By combining the effect of the injection current with the grating tuning, the total tuning bandwidth of the external cavity quantum-dot laser can reach up to 85 nm. The dependence of the threshold current on the tuning wavelength is also presented.     

Experimental results of DPIS with a new RFQ

We have developed a new heavy ion production system which uses a combination of an RFQ and a laser ion source. Induced plasma by a laser shot is delivered to the RFQ without an extraction electrode. We named this new idea ‘direct plasma injection scheme (DPIS)’. In 2004, a new RFQ was built for demonstrating the capability of the DPIS. After a few months of commissioning period, we could obtain more than 60 mA of carbon beam from the RFQ. This new scheme could be applied to cancer therapy facilities and high energy nuclear physics accelerator complexes.     

A low-threshold and high-power oxide-confined 850-nm AlInGaAs strained quantum-well vertical-cavity surface-emitting laser

A low-threshold and high-power oxide-confined 850-nm AlInGaAs strained quantum-well (QW) vertical-cavity surface-emitting laser (VCSEL) based on an intra-cavity contacted structure is fabricated. A threshold current of 1.5 mA for a 22 μm oxide aperture device is achieved, which corresponds to a threshold current density of 0.395 kA/cm². The peak output optical power reaches 17.5 mW at an injection current of 30 mA at room temperature under pulsed operation. While under continuous-wave (CW) operation, the maximum power attains 10.5 mW. Such a device demonstrates a high characteristic temperature of 327 K within a temperature range from -12℃ to 96℃ and good reliability under a lifetime test. There is almost no decrease of the optical power when the device operates at a current of 5 mA at room temperature under the CW injection current.     

Output characteristics of a simple FP-LD/FBG module

We propose a simple laser diode module that consists of a Fabry–Perot laser diode (FP-LD) and a fiber Bragg grating (FBG) for a compact, stable and low-cost wavelength division multiplexing light source. The spectral bandwidth of the laser output from the FP-LD/FBG module was measured to be 0.024 nm. The side mode suppression ratio (SMSR) was 44.42 dB at the injected electric current of 14 mA and at 25 °C. Both the BER characteristics and the eye diagram were measured, and they confirmed that the present laser diode module could be used as an alternative configuration for a low-cost light source.     

A new design of pulsed laser diode driver system for multistate quantum key distribution

In this paper, we describe a new design of laser diode driver system based on MOSFET current mirror and digital signal controller (DSC). The system is designed to emit stream pairs of photons from three semiconductor laser diodes. The DSC is able to switch between the three laser diodes at constant rate. The duty cycle is maintained at 1% in order to reduce its thermal effect and thus prolong the laser diodes’ life cycles. The MOSFET current mirror circuits are capable of delivering constant modulation current with peak current up to 58 mA to each laser diode. This laser driver system will allow the generating biphotons automatically with qubit rate around 8-13% for μ less than or equal to 1, thus making it practical for six-states quantum key distribution implementation.     

2.45GHz ECR 强流等离子体源核心部件设计与实验研究

电子回旋共振(Electron Cyclotron Resonance,ECR)等离子体源能产生高电荷态离子、高流强的单电荷态离子,提供稳定的束流和良好的重复性.核心部件的设计对ECR等离子体源是至关重要的,磁场对等离子体的生成和分布有直接影响,良好的磁场可以提高等离子体的性能和效率.采用有限元分析方法对ECR等离子体源磁场进行分析与设计,得到了满足设计需求与目标的磁场位形,通过高斯计对设计的永磁环轴向磁场精确测量,发现磁场仿真结果与实验结果吻合比较好,只是轴向磁场最大值及对应位置上有点偏差.通过集成实验,研究核心部件对离子源引出束流强度的影响,引出束流稳定且强度达到7 m A.