共查询到20条相似文献,搜索用时 609 毫秒
1.
High-order optical harmonic generation from solid surfaces 总被引:1,自引:0,他引:1
During the interaction of an intense ultrashort laser pulse with solid targets, a thin layer of surface plasma is generated in which the density drops to the vacuum level in a distance much shorter than the wavelength. This sharp plasma-vacuum boundary performs an oscillatory motion in response to the electromagnetic forces of the intense laser light. It is shown that the generation of reflected harmonics can be interpreted as a phase modulation experienced by the light upon reflection from the oscillating boundary. The modulation side-bands of the reflected frequency spectrum correspond to odd and even harmonics of the laser frequency. Retardation effects lead to a strong anharmonicity for high velocities of the plasma-vacuum boundary. As a result, harmonic generation is strongly enhanced in the relativistic regime of laser intensities.Prof. F. P. Schäfer on the occasion of his 65th birthday. 相似文献
2.
将一类色散介质的介电常数写成有理分式函数形式,进而导出FDTD中电位移矢量D和电场强度E之间的关系,形成SO-FDTD方法. 应用该方法计算了冷等离子体平板对电磁波的反射系数,通过与解析结果的比较,验证了该算法的高效性和高精度,同时,应用SO-FDTD方法,计算了等离子体层对垂直入射电磁波的反射系数,结果表明:等离子体厚度、电子密度、电子密度的分布形式和入射波频率是影响反射系数的重要因素.
关键词:
等离子体
电磁波
FDTD方法 相似文献
3.
The effect of negative ions on the drift wave instability has been studied in detail in a linear device by means of Langmuir probes and cross‐correlation analysis. Drift waves are excited in low‐density (5 × 1014 m–3) and strongly magnetized (0.5 T) pure argon plasmas and in the presence of an oxygen admixture. The radial density profile of negative ions is hollow. For increasing concentration of negative ions the wave frequency decreases by about 25%. Despite of an axial density gradient, a global wave frequency is established for the entire column length. While for the noble gas case the drift wave frequency is given by the equilibrium plasma parameters in the mid‐plane, there is no such relationship for the argon plasma with oxygen admixture. This different finding is attributed to the inhomogeneous distribution of the negative ions (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
4.
A.B. Mikhailovskii A.P. Churikov V.D. Pustovitov S.V. Konovalov 《Physics letters. A》2008,372(18):3274-3276
Instabilities responsible for magnetic turbulence in laboratory rotating plasma are investigated. It is shown that the plasma compressibility gives a new driving mechanism in addition to the known Velikhov effect due to the negative rotation frequency gradient. This new mechanism is related to the perpendicular plasma pressure gradient, while the density gradient gives an additional drive depending also on the pressure gradient. It is shown that these new effects can manifest themselves even in the absence of the equilibrium magnetic field, which corresponds to nonmagnetic instabilities. 相似文献
5.
FDTD Analysis of Electromagnetic Reflection by Conductive Plane Covered with Magnetized Inhomogeneous Plasmas 总被引:2,自引:0,他引:2
Shaobin Lui Jinjun Mo Naichang Yuan 《International Journal of Infrared and Millimeter Waves》2002,23(12):1803-1815
A novel finite-difference time-domain (FDTD) methodology which incorporates both anisotropy and frequency dispersion at the same time is developed for electromagnetic wave propagation in anisotropic magnetoactive plasmas in this paper. The numerical verification of the method are confirmed by computing the reflection and transmission of right-handed/left-handed circularly polarized (RCP/LCP) wave through a magnetized plasma layer, with the direction of propagation parallel to the direction of the biasing field. And, the right-handed / left-handed polarized wave reflection coefficients for electromagnetic signals normally incident upon a conductive plane covered with a layer of magnetized plasma are computed using the new FDTD method. The parabolic electron-number density profile varies only in the direction perpendicular to the plane. The function dependence of reflection coefficients on the number density, collision frequency and external magnetic field is studied. 相似文献
6.
Electromagnetic Reflection of Conductive Plane Covered with Magnetized Inhomogeneous Plasma 总被引:2,自引:0,他引:2
Jiaming Shi Yong Gao Jiachun Wang Zhongcai Yuan Yongshun Ling 《International Journal of Infrared and Millimeter Waves》2001,22(8):1167-1175
This paper presents numerical results in the form of graphs of the power reflection coefficients for electromagnetic signals normally incident upon a conductive plane covered with a layer of plasma. The plasma's electron density varies only in the direction perpendicular to the plane. A non-uniform external magnetic field, which is oriented in a direction paralleled to the conductor's surface and has a gradient normal to this surface, is applied to the plasma. Parameters considered in the computation cover a relatively wide range and the functional dependence of the power reflection coefficients on these parameters are studied. 相似文献
7.
The dynamic nature of the ion wake formed downstream a dust particle immersed in a plasma with flowing ions has been investigated via Particle-in-Cell simulation. It is found that the wake oscillates in time and the motion is characterized by some dominant frequencies. By means of signal processing analysis, three harmonics are detected (two at low frequencies and one at high frequencies) and compared to the characteristic plasma frequencies given by the dispersion relations for ions and electrons. Good matching is found between the high frequency harmonic and the electron plasma frequency, and between the low frequency harmonics and the ion acoustic and ion plasma frequencies. 相似文献
8.
Bacal Martha Doucet H. J. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1973,1(3):91-99
The scope of this research is to investigate experimentally electron (ne), negative ion (n-) and positive ion (n+) densities characterizing laboratory negative ion-rich plasmas, produced by electron attachment in N2O3, O2 and I2, and to find out the factors limiting the achievement of very low ? (relative electron density ? = ne/n+). These plasmas may be of great interest for the production of negative ion beams. It is shown experimentally that it is possible to produce plasmas with a high proportion of negative ions (n-/n+ ? 90 %) and a low proportion of electrons, at densities n+ up to 1011 cm-3. The comparison of mass spectrometric data with kinetic calculations leads to the conclusion that the loss of negative ions by diffusion limits the lowest ? achieved at low ion density (n+ < 109 cm-3). At higher ion density, mutual neutralization seems to control the ? values. A general limitation seems to exist for the lowest ? attainable in small plasmas produced by electron attachment : the confinement of negative ions in a plasma is due to the presence of electrons and therefore this confinement becomes inefficient when ? drops to values as low as 10-3. 相似文献
9.
Propagation of both low and high frequency waves in a plasma consisting of electrons, ions, positrons and charged dust particles
have been theoretically studied. The characteristics of dust acoustic wave propagating through the plasma has been analysed
and the dispersion relation deduced is a generalization of that obtained by previous authors. It is found that nonlinear localization
of high frequency electromagnetic field in such a plasma generates magnetic field. This magnetic field is seen to depend on
the temperatures of electrons and positrons and also on their equilibrium density ratio. It is suggested that the present
model would be applicable to find the magnetic field generation in space plasma. 相似文献
10.
S N Antani 《Pramana》1975,4(4):184-191
In this work, we present numerical computation of anomalous absorption of a powerful electromagnetic wave incident normally,
on an isothermal plasma with a linear density gradient. We consider first, the “intensity” dependence of anomalous absorption
treating two important cases: one that of a typical high temperature, high density fusion plasma occurring in a laser-pellet
application and the other that of an ionospheric (F-layer) plasma. It is found that for low incident powers, reflection is
almost constant, corresponding essentially, to classical electronion collisions. As we increase the incident power, however,
we find that the reflection starts dropping and the absorption takes over. This result is interpreted in terms of the instability
generated anomalous absorption of the incident wave. Next, we consider the “wavelength” dependence of anomalous absorption,
wherein we observe that the effect of anomalous absorption is increasing for longer wavelengths of the incident laser radiation. 相似文献
11.
Three kinds of electrostatic modes are experimentally observed to propagate along magnetic-field lines for the first time in the pair-ion plasma consisting of only positive and negative fullerene ions with an equal mass. It is found that the phase lag between the density fluctuations of positive and negative ions varies from 0 to pi depending on the frequency for ion acoustic wave and is fixed at pi for an ion plasma wave. In addition, a new mode with the phase lag about pi appears in an intermediate-frequency band between the frequency ranges of the acoustic and plasma waves. 相似文献
12.
P. Zobdeh R. Sadighi‐Bonabi H. Afarideh E. Yazdani R. Rezaei Nasirabad 《等离子体物理论文集》2008,48(8):555-560
In this work we evaluate the interaction of high intense laser beam with a steepened density profile. During laser interaction with underdense plasma by freely expanding plasma regime, modification of density profile is possible. In this paper we have investigated the ultra short laser pulse interaction with nonisothermal and collisionless plasma. We consider self–focusing as an effective nonlinear phenomenon that tends to increase when the laser power is more than critical rate. By leading the expanded plasma to a preferred location near to critical density, laser reflection is obtained, so the density profile will be locally steepened. The electromagnetic fields are evaluated in this new profile. We show the amplitude and period of electrical field oscillation are increased by reducing the steepened scale length. Also our numerical results identify that by reducing the steepened scale length, the electrical field is increased to wave breaking threshold limit. This high gradient electrical field causes the effective beam loading during the wave breaking phenomenon. The wave breaking can be the initial point for other acceleration regime as cavity or channel guiding regime. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
13.
Small amplitude double layers in an electronegative dusty plasma with q-distributed electrons 下载免费PDF全文
The small amplitude dust ion-acoustic double layers in a collisionless four-component unmagnetized dusty plasma system containing nonextensive electrons, inertial negative ions, Maxwellian positive ions, and negatively charged static dust grains are investigated theoretically. Using the pseudo-potential approach and reductive perturbation method, an energy integral equation for the system has been derived and its solution in the form of double layers is obtained. The results appear that the existence regime of the double layer is very sensitive to the plasma parameters, e.g., electron nonextensivity,negative-to-positive ion number density ratio etc. It has been observed that for the selected set of parameters, the system supports rarefactive,(compressive) double layers depending upon the degree of nonextensivity of electrons. 相似文献
14.
Chauhan S.S. Dahiya R.P. Seungjun Yi Lonngren K.E. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1997,25(6):1425-1430
The variable coefficient modified Korteweg-de Vries (mKdV) equations for incident and reflected solitons are derived and solved to study the reflection of compressive and rarefactive ion acoustic solitons at the critical density in an inhomogeneous negative ion plasma. The polarity of the incident compressive and rarefactive solitons is not altered during the reflection process. Increasing the density gradient reinforces the reflection of both compressive and rarefactive mKdV solitons, whereas enhancement of the unperturbed plasma density weakens the reflection 相似文献
15.
The soliton formation by the current-driven drift-like wave is investigated for heavier ion (such as barium) plasma experiments planned to be performed in future. It is pointed out that the sheared flow of electrons can give rise to short scale solitary structures in the presence of stationary heavier ions. The nonlinearity appears due to convective term in the parallel equation of motion and not because of temperature gradient unlike the case of low frequency usual drift wave soliton. This higher frequency drift-like wave requires sheared flow of electrons and not the density gradient to exist. 相似文献
16.
The reflection of protons from a partially cesiated tungsten surface is studied in the energy domain between 100 and 2000 eV and in the angular domain between 75° and 85° with respect to the surface normal. The study is performed by measuring the angular and energy distribution of the scattered negative ions. The reflection can take place along two paths. One path is reflection from the cesium surface layer, the other one is reflection from the tungsten substrate. A dependence of the final charge state on the path is observed. It is inferred that this phenomenon is due to incomplete neutralization of the protons scattered from the cesium layer. The energy loss of the reflected ions cannot be accounted for by using only the binary collision model. Also the electronic stopping of the atoms by the metal electrons is shown to be an important energy loss mechanism. Total conversion measurements of H+ to H- combined with the measurements of the negatively charged fraction of the scattered particles, as reported in the proceeding paper, yield the particle reflection coefficient as a function of the angle of incidence. These reflection coefficients show that for angles of incidence less than 75° already more than 50% of the particles do not reflect from the surface. Total conversion efficiency measurements with H- ions as primary ions show that the influence of the initial charge state on the total conversion is very small. 相似文献
17.
本文建立了时变非磁化等离子体平板的一维模型,并采用时域有限差分(FDTD)方法对太赫兹(THz)电磁波在时变等离子体中传播时的反射、透射系数及吸收率进行了计算.然后根据计算结果分析了时变等离子体的上升时间、电子密度、温度以及等离子体平板厚度等参数对不同频段THz波在等离子体中传播特性的影响.分析结果表明:THz波在时变等离子体中传播时,其反射系数受等离子体电子密度和上升时间的影响较大;而吸收率则随着上升时间的减小、电子密度及平板厚度的增加而增大;此外,THz电磁波能够穿透量级为1020m-3的高密度等离子体层,可以作为再入段飞行器通信以及高密度等离子体诊断的理想工具. 相似文献
18.
A. V. Kashevarov 《Technical Physics》2005,50(4):421-426
The problem is considered of the probe diagnostics of a moving, weakly ionized, collision-dominated plasma containing singly
charged negative ions or dust grains (heavy multicharged ions). Based on an asymptotic analysis, expressions are obtained
that describe the saturation current densities of the electrons and of the charged particles of other species at the point
where the plasma flowing around a spherical probe in the laminar boundary layer regime stagnates. 相似文献
19.
20.
Shaobin Liu Wei Hong Naichang Yuan 《International Journal of Infrared and Millimeter Waves》2006,27(3):403-423
The plasma photonic crystal is a periodic array composed of alternating thin unmagnetized (or magnetized) plasmas and dielectric
materials (or vacuum). In this paper, the piecewise linear current density recursive convolution finite-difference time-domain
method for the simulation of isotropic unmagnetized plasma is applied to model unmagnetized plasma photonic crystal structures.
A perfectly matched layer absorbing material is used in these simulations. In time-domain, the electromagnetic propagation
process of a Gaussian pulse through an unmagnetized plasma photonic crystal is investigated. In frequency-domain, the reflection
and transmission coefficients through unmagnetized plasma photonic crystals are computed and their dependence on plasma frequency,
plasma thickness, collision frequency is studied. The results show theoretically that the electromagnetic bandgaps of unmagnetized
plasma photonic crystals are tuned by the plasma parameters. 相似文献