共查询到19条相似文献,搜索用时 156 毫秒
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根据球对称激光等离子体空气冲击波在自由空间中传输的约束条件,对多光子非线性Compton散射的强激光等离子体空气冲击波波前的传输特性进行了研究,给出了散射下空气冲击波波前的运动方程,并进行了数值模拟。结果表明:该冲击波的衰减过程不仅与爆炸源和爆炸过程的特性、释放总能量、空气的弹性有关,而且还与散射有关,散射效应使冲击波的初始半径增大,衰减过程加快,能量转移率提高;数值模拟与实验结果符合得很好。 相似文献
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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 相似文献
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激光医学应用从60年代眼科开始,现在已有广泛应用.本文介绍一项新进展──激光产生等离子体及等离子体冲击波的临床医学应用.其关键是“阈值”.当激光功率达到阈值时,产生等离子体及等离子体冲击波,等离子体冲击波的波前压强可达1~500kbar,能切割组织,粉碎结石.由于不同组织具有不同的阈值,切割是具有选择性的。等离子体扩展到一定程度产生“空化气泡”,空化泡的直径与激光能量E~(1/3)有关. 相似文献
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冲击波是天体物理观测中常见的现象, 其对粒子的加速被认为是高能宇宙射线的来源. 宇宙中冲击波周围往往存在很强的磁场, 但人们对于此类强磁场的产生放大过程的理解并不充分. 本文利用二维粒子模拟程序研究了激光与磁化或者非磁化等离子体相互作用产生的冲击波现象, 给出了冲击波波前处磁场的产生放大特性. 研究发现, 作用过程中的自生磁场可以储存能量, 从而进一步加速电子; 当存在外加磁场时, 由冲击波加速的电子和离子的能量都比同条件下非磁化等离子体的能量高; 而且外加磁场藉由冲击波放大倍数则与其值有极大关系. 与天文观测中推断的磁场与背景磁场相比放大千倍这一研究结果的比较可以看出, 天体冲击波周围磁场放大主要是由局域内生磁场导致的. 相似文献
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为了研究激光击穿空气产生的等离子体爆轰波形成机制和传播规律,利用高能量CO2激光器产生强激光,进行了空气中产生激光支持等离子体爆轰波实验。实验中:设置了诱导靶板,用于诱发和定位空气中的激光支持爆轰波;以激光器升压过程球隙放电产生的光信号作为触发源,触发高时间分辨率(纳秒级)的高速相机,记录了激光支持爆轰波的成长和传播全过程。分析了激光支持爆轰波的形成机理和传播规律。采用C-J爆轰理论,计算了激光支持爆轰波的压力和温度。研究结果表明:激光支持等离子体爆轰波形成初期,等离子体爆轰波发光体为球形;随着时间增加,等离子体爆轰波发光体的形状类似流星,且头部为等离子体前沿吸收层,亮度较高,而尾部等离子体温度较低,亮度较弱。等离子体爆轰波高速向激光源的方向移动,爆轰波速度高达18 km/s,温度约为107K。随着激光强度的减弱,爆轰波速度迅速按指数规律衰减,当爆轰波吸收的激光能量不能有效支持爆轰波传播时,爆轰波转变为冲击波。 相似文献
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A theoretical model is proposed to describe the mechanism of
laser-induced plasma shock wave evolution in air. To verify the
validity of the theoretical model, an optical beam deflection technique
is employed to track the plasma shock wave evolution process. The
theoretical model and the experimental signals are found to be in
good agreement with each other. It is shown that the laser-induced
plasma shock wave undergoes formation, increase and decay processes;
the increase and the decay processes of the laser-induced plasma
shock wave result from the overlapping of the compression wave and
the rarefaction wave, respectively. In addition, the laser-induced
plasma shock wave speed and pressure distributions, both a
function of distance, are presented. 相似文献
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Shadowgraph investigation of plasma shock wave evolution from Al target under 355-nm laser ablation
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The propagation of a plasma shock wave generated from an Al target surface ablated by a nanosecond Nd:YAG laser operating at 355 nm in air is investigated at the different focusing positions of the laser beam by using a time-resolved shadowgraph imaging technique. The results show that in the case of a target surface set at the off-focus position, the condition of the focal point behind or in front of the target surface greatly influences the evolution of an Al plasma shock wave, and an ionization channel forms in the case of the focal point set in front of the target surface. Moreover, it is found that the shadowgraph with the evolution time around 100 ns shows that a protrusion appears at the front tip of the shock wave if the focal point is at the target surface. In addition, the calculated results of the expanding velocity of the shock wave front, the mass density, and pressure just behind the shock wave front are presented based on the shadowgraphs. 相似文献
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针对超高压下透明材料的高压离化机理,分析了透明材料中冲击波直接诊断技术的基本方法. 利用Drude-自由电子气模型,分析了不同冲击压力下冲击波阵面反射率的变化. 从理论上比较了不同探针光波长反射率的区别,发现探针光波长为660 nm时比探针光波长为532 nm时获得的冲击波阵面反射率要高. 对探测器"致盲"问题也进行了研究. 通过分析反射信号的时间顺序和强度大小,发现"致盲"效应是由X光对透明窗口离化引起的. 同时,发现方波驱动脉冲平台的前沿到达时刻和X光离化效应出现的时刻相同,冲击波信号到达时刻晚于X光离化时刻. 通过实验结果,得到蓝宝石中冲击波速度为35 km/s时,其波阵面的反射率约为40%. 通过理论分析和实验数据比对的方法,验证了蓝宝石中的减速曲线. 给出了加蓝宝石窗口后的测速公式. 经过和实验对比,确认了测速公式的正确性.
关键词:
冲击波
光学诊断
成像
干涉仪 相似文献
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本文研究了等离子体消融所造成的激波,找出了位于激波波前及消融波前的各流体动力学参量间的相互依赖关系,对消融激波的生成与时间发展过程进行了描述。 相似文献
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针对超高压下透明材料的高压离化机理,分析了透明材料中冲击波直接诊断技术的基本方法。利用Drude自由电子气模型,分析了不同冲击压力下冲击波阵面反射率的变化。设计了专门的实验,将探测器致盲区与信号区错开,获得了蓝宝石中冲击波阵面反射的信号。结果表明:冲击波速度为32 km/s时,其波阵面的反射率约为35%,致盲效应出现时间与激光脉冲峰值到达时刻相同,持续时间也与激光脉宽相同。分析了致盲应产生的原因,并提出了解决办法。给出了加蓝宝石窗口后的测速公式,经过和实验对比,确认了测速公式的正确性。 相似文献
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A mechanism of action of a shock wave on an active medium, which leads to an additional energy release source, is considered.
This source moves together with the shock wave front and depends on the magnitude and direction of the electric field applied
to the plasma and on the current density in the plasma. The study is a continuation of an earlier publication devoted to the
propagation of weak shock waves. Here, we consider shock waves of an arbitrary intensity with an arbitrary mechanism of formation
of an additional energy contribution due to variation of the parameters of the medium as a result of passage of the shock
wave. Special cases of this effect are the propagation of a shock wave in a plasma and detonation burning. 相似文献
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通过平板冲击实验研究了富含微缺陷的非均质脆性固体的冲击压缩响应特性.选取“强角闪石化橄榄二辉岩”作为样品材料,利用激光速度干涉仪测量样品后自由面的速度历史,在冲击加载应力远低于样品材料Hugoniot弹性极限的条件下,观测到了表征破坏波出现的再加载信号,并且该破坏波的速度远大于玻璃中破坏波的速度,以接近于冲击波的速度在样品内向前传播,其形成机理与玻璃样品中的破坏机理不同,称之为“就位扩展机理”.采用同一冲击加载应力(~3.9GPa)作用于不同厚度的样品,获得了破坏波穿过样品的运动过程,确定出样品中破坏波的轨迹线近似为一条不过原点的直线,相应的产生此破坏波的弛豫时间约为0.5 μs. 相似文献
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Channels are traditionally machined in materials by drilling from the front side into the bulk. The processing rate can be
increased by two orders of magnitude for transparent materials by growing the channel from the rear side. The process is demonstrated
using nanosecond laser pulses to drill millimeter-sized channels through thick silica windows. Absorbing defects are introduced
onto the rear surface to initiate the coupling of energy into the material. Laser drilling then takes place when the fluence
exceeds a threshold. The drilling rate increases linearly with fluence above this threshold. While UV light drills about four
times faster than IR light, the pulse length (in the nanosecond regime) and the pulse repetition rate (in the 0.1–10 Hz range)
do not greatly influence the drilling rate per pulse.
Drilling rates in excess of 100 μm per pulse are achieved by taking advantage of the propagation characteristics of the plasma
created at the drilling front. The plasma during rear-side drilling generates a laser-supported detonation wave into the bulk
material. The geometry also seems to increase the efficiency of the laser-induced plasma combustion and shock wave during
the pulse by confining it in front of the channel tip.
Received: 1 July 1999 / Accepted: 17 April 2000 / Published online: 20 September 2000 相似文献