首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到18条相似文献,搜索用时 234 毫秒
1.
用声学诊断方法对超短脉冲强激光在空气中传输形成的等离子体通道进行了测量,根据通道不同位置的声音信号,得到了通道的长度和通道内电子密度等信息. 关键词: 声学测量 等离子体通道  相似文献   

2.
空气中激光等离子体通道导电性能的研究   总被引:15,自引:0,他引:15       下载免费PDF全文
超强飞秒激光在大气中传输时,可以形成很长的等离子体通道.对通道电阻率和测量电极与等离子体通道间的接触电阻进行了测量,并对影响等离子体通道电阻率的主要因素进行了研究分析.提出减小等离子体通道电阻的方案. 关键词: 等离子体通道 电阻率 接触电阻  相似文献   

3.
郝作强  张杰  俞进 《物理》2004,33(6):443-445
超短脉冲强激光在空气中传输可以形成很长的等离子体通道,目前对这种等离子体通道有许多诊断方法,文章介绍了一种十分简易但很有效的方法——声学测量方法.该方法可以根据通道不同位置的声音信号,测量通道的长度和通道内电子密度等一些参数,具有其他传统诊断方法无可比拟的优越性.  相似文献   

4.
利用皮秒和飞秒激光研究了激光在空气中聚焦产生单个等离子体通道的条件.研究发现,能量为8—12mJ皮秒激光被焦距为15cm的透镜聚焦后,可以产生较为稳定的单个通道.通过横向纵向阴影成像分析发现,通道的管壁对聚焦产生的自发光具有箍缩作用,而通道内部却有利于光的传输.同时还发现,当采用短焦距透镜时,能量低于10mJ的飞秒激光在空气中较易形成单个等离子通道. 关键词: 等离子体通道 皮秒激光 飞秒激光 阴影成像  相似文献   

5.
基础知识学习与知识综合应用的脱节一直困扰着大学基础物理教学。由于空气自聚焦效应和等离子体散焦效应共同导致的飞秒激光成丝现象是强激光非线性光学研究的热点话题。为了培养学生的对光学、原子物理学、电子学、数值分析和机械制图等基础知识的综合应用能力,和学生一起设计了创新演示实验去探究飞秒激光成丝过程。采用荧光测量和声音测量两种方法对比研究光丝在不同位置处的演化情况。  相似文献   

6.
研究了飞秒激光诱导单个空气等离子体通道的吸收和辐射特性,给出了等离子体通道吸收系数的解析表达式,并理论推导出了辐射能流率的表达式。与TOPS不透明度数据库查表方法比较,两种方法计算结果符合得很好。分析了吸收和辐射参量对入射激光参量的依赖关系。计算了中心波长800nm,脉宽40fs的飞秒激光空气等离子体通道的吸收和辐射参量的典型数值。结果表明,成单丝情况下等离子体通道的Rosseland吸收系数为0.0270cm-1,辐射能流率为7.87×1010W/m2;窄脉宽长波长的入射激光有利于生成吸收小辐射强的等离子体通道。  相似文献   

7.
放电等离子体光谱技术及激光诱导击穿光谱技术由于实验系统相对简单、信号强,很早就被应用于组分测量领域。由于自由放电在时间和空间上都具有随机性,这使得放电等离子体空间分辨光谱的精确测量变得十分困难;而激光诱导击穿光谱技术又局限于点测量。介绍了一种基于飞秒激光诱导的放电等离子体一维空间分辨光谱的高精度测量方法。飞秒激光自聚焦可以形成一段丝状弱等离子体通道,将该等离子体通道靠近高压直流脉冲电极时,可作为高压电极放电的触发源。这种触发方式可在规定的时刻触发高压电并诱导其沿着等离子体通道的路径击穿气体。实验多次测量放电开始时刻与激光到达时刻的时间间隔的波动小于0.01μs,证实了使用本方法诱导高压放电具有很高的重复性。由此可知,利用飞秒激光自聚焦成丝产生的弱等离子体通道诱导高压放电,可实现对高压放电的空间和时间的精确控制,进而可以采集放电等离子体通道的一维空间分辨光谱。实验结果表明,在喷管结构主导的流场环境中,由于喷管中纯N_2与喷管外空气的组分不同,在高空间分辨光谱中,可以清晰地看到一维等离子体通道上不同位置的组分浓度变化情况。在一维空间分辨光谱中将N~+和O光谱信号强度与N_2和O_2的浓度进行关联,可实现流场组分的一维在线诊断。该方法不仅具有纳秒激光诱导击穿光谱技术的相同优点,还具有一维空间分辨能力,在组分一维精确测量方面极具优势。同时,该方法还有望实现高时间分辨测量,对研究放电等离子体的时空演化过程具有重要的意义。  相似文献   

8.
任玉  李付锦  董旭  林景全 《中国光学》2012,5(2):133-142
基于强飞秒激光诱导等离子体通道的基本性质,分析了等离子体通道在传导电能和射频电磁能时的一些基本问题。综述了飞秒激光等离子体通道传输电能和电磁能方面的新概念和新技术,重点描述了该领域近几年所取得的一些理论及应用的最新成果。最后,展望了飞秒激光等离子体通道在传导能量技术领域中的发展趋势。  相似文献   

9.
应用多光子非线性Compton散射模型、空间动态补偿模型、非线性薛定谔方程和数值模拟方法,研究了Compton散射对超强飞秒激光等离子体中通道的影响,提出了将Compton散射光作为形成等离子体通道的新机制,给出了超强飞秒激光脉冲在等离子体中传播和电子密度随时间变化的非线性修正方程,并进行了数值模拟.研究发现:散射使等离子体中电子密度峰值增大1个量级,半径增大1 mm.激光最大功率密度被限制在10~(18)W/m~2以下,随传输距离增大缓慢衰减.传输初始阶段,单脉冲衰减能量较散射前增大2%,之后衰减较平缓.通过增加超强飞秒激光脉冲输入功率,能有效地增加电子密度峰值,有利于等离子体通道的形成.并对所的结论给出了初步物理解释.  相似文献   

10.
1kHz飞秒激光脉冲在空气中传输成丝的演化过程   总被引:1,自引:1,他引:0       下载免费PDF全文
利用高重复频率(1kHz)、低能量的飞秒激光脉冲研究激光脉冲在空气中传输成丝的演化过程.采用成像的方法观测飞秒激光脉冲在大气传输过程中光束截面上光强分布变化,以及大气等离子体通道对光强分布的反作用.实验结果表明,激光脉冲在传输过程中先形成双丝结构,再逐渐合并成单丝结构.实验结果与利用非线性薛定谔方程耦合多光子电离的数值模拟结果基本一致. 关键词: 飞秒激光脉冲 等离子体通道 成像  相似文献   

11.
The longitudinal plasma profile of a laboratory scale filament induced by the propagation of an intense femtosecond laser pulse in air was measured simultaneously by three different methods. Each of them is based on a specific property of the filament, including electromagnetic pulse emission, backward emitted nitrogen fluorescence, and acoustic wave generation. Although each of above methods has been separately reported, it is the first time that a simultaneous multi-parameter measurement on a laser filament is presented. Such multiparameter measurement allows a direct comparison between the different methods, and a better understating of the dynamics of a filament from its generation through multi-photon/tunnel ionization (MPI/TI) to its damping through acoustic wave emission. The advantages as well as drawbacks of each method are analyzed in a comparative way. PACS 42.65.Jx; 42.68.Ay; 42.68.Wt  相似文献   

12.
Long plasma channels in air induced by femtosecond laser pulses are investigated using three different methods, including the cross-section imaging, resistivity measuring and acoustic diagnostics. These methods are based on different properties of the light filaments. A comparison of the three diagnostics shows that the imaging method is the most precise one in studying the filaments distribution and evolution, that the sonographic method is the most convenient approach to detecting long plasma channels by detecting the acoustic wave generation, and that the resistivity measurement can only be applied for giving a rough estimate. The diagnostics of filaments allow us to choose appropriate detecting methods and provide further insight into the dynamic evolution of the light filaments in air.  相似文献   

13.
Sea-surface movement in the ocean induces a time-varying acoustic channel which affects underwater system including acoustic communication. For an investigation of surface movement effects on communication channel parameters (delay time, amplitude, etc.), acoustic transmission and reception experiments were conducted in the water tank. The delay time and amplitude of single surface bounce path from the measurement data show periodic time dependence, which is caused by a travelling periodic sinusoidal surface. A ray-based propagation model is applied to the experimental environment to estimate communication channel parameters. A comparison between measurement data and model result permit a physical interpretation of the communication channel parameters. The difference of single surface bounce path delay times from the model and measurement data are within small error bound. The delay times oscillate around the delay time of single surface bounce path when the surface is flat and show the periodic sine function. The amplitudes from the model are in agreement with those from the measurement data except at low amplitude region. Slight angle and frequency dependencies of source and receiver and noise in the water tank account for the disagreement in this region. Since the crest and trough of surface wave respectively make the acoustic energy emitted from the source converge and diverge, the amplitudes have high fluctuation and same phase with the delay time. The ray model is applied to an environment in the ocean. A striation pattern appears in surface reflected signal due to shadow zone on the surface.  相似文献   

14.
HELS法在循环平稳声场全息重建中的理论与实验研究   总被引:1,自引:0,他引:1       下载免费PDF全文
张海滨  万泉  蒋伟康 《物理学报》2009,58(1):333-340
Helmholtz 方程最小二乘法利用一组球面波基函数拟合声源产生的声场,根据重建和实际声压的误差最小原则,利用最小二乘法确定基函数展开的项数以及对应的权重系数,该方法具有计算效率高和需要测点少的优点,在实际工程中有很大的实用性.Helmholtz 方程最小二乘法和其他近场声全息方法一样都是针对平稳声场,对非平稳声场的分析很少.对于实际工程中经常遇到的一类特殊非平稳声场——循环平稳声场,现有的技术多以单通道信号分析为主,其高阶统计量在故障诊断领域应用较广.分析了循环平稳声场中Helmholtz方程最小二乘 关键词: 声全息 循环平稳 Helmholtz 方程 球面波  相似文献   

15.
P K Karmakar 《Pramana》2007,68(4):631-648
Application of inertia-induced acoustic excitation theory offers a new resonant excitation source channel of acoustic turbulence in the transonic domain of plasma flow. In bi-ion plasmas like colloidal plasma, two well-defined transonic points exist corresponding to the parent ion and the dust grain-associated acoustic modes. As usual, the modified ion acoustic mode (also known as dust ion-acoustic (DIA) wave) dynamics associated with parent ion inertia is excitable for both nanoscale-and micronscale-sized dust grains. It is found that the so-called (ion) acoustic mode (also known as dust-acoustic (DA) wave) associated with nanoscale dust grain inertia is indeed resonantly excitable through the active role of weak but finite parent ion inertia. It is interestingly conjectured that the same excitation physics, as in the case of normal plasma sound mode, operates through the active inertial role of plasma thermal species. Details of the nonlinear acoustic mode analyses of current interest in transonic domains of such impure plasmas in hydrodynamic flow are presented.   相似文献   

16.
The properties of arctic underwater acoustic channel were researched using BurkeTwersky(BT) model and ray theory.In the BT model,sea ice ridge is assumed as a set of semi-elliptical cylinder randomly distributed on a stress-free surface.By approximation of low frequency and high frequency of the BT model,the reflection coefficients were calculated at different frequencies.On the basis of ray theory,the acoustic field was calculated and the properties of underwater acoustic channel was analyzed.Compared to underwater acoustic channel properties when the boundary is air,the results show that under the ice surface some sound rays disappear during transmission,because the ice surface reflection coefficients is less than absolute soft surface.Especially,the higher the frequency,the higher the under-ice transmission loss.As a result,under-ice condition is unfavourable for acoustic signals to travel far.Besides,as to the channel structure,the reflection coefficient of ice layer is smaller,the channel multi-path structure is not significant compared to water-air interface without ice.The research results are valuable for our understanding of hydroacoustic channel and the prediction of the sonar system working in the polar region.  相似文献   

17.
Two wide spreaded methods for the measurement of plasma fluctuations are investigated both theoretically and experimentally. In limited regions of frequency and wave number, the fluctuation amplitudes obtained by probes and optical line radiation show sufficient good agreement; in general, however, different effects must be eliminated in order to obtain quantitative values. As an application, a transition from isothermal ion acoustic turbulence to a hybrid turbulent state including temperature fluctuations in a low pressure d.c. plasma has been discovered.  相似文献   

18.
采用SI—PIN半导体探测器、^241Am激发源和2048通道分析器及自行研制的SI—PIN 2000便携式X荧光分析仪,对钒钛磁铁矿直接粉末样品中Ti,V,Cr,Mn,Fe,Co,Ni,Cu等8个主、次元素进行了分析应用研究。文章叙述了所采用的直接粉末样品法的样品盒结构、基体校正的α系数计算方法、重叠干扰校正原则和漂移校正的方法,并且给出了所选择的分析条件和样品制备方法,分析过程简单、结果准确、分析速度快,特别适应矿山、冶金的生产原料分析需要,有良好的应用前景,与封闭正比计数器X射线荧光分析仪相比,检出限降低了1个数量级。  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号