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1.
We investigate the nonlinear evolution of the backward stimulated Raman scattering (BSRS) in the regime where the nonlinear saturation mechanism is the Langmuir decay instability resulting from the coupling of the BSRS-generated Langmuir wave with the ion acoustic waves. We present numerical results obtained with a fluid-type code in one- and two-dimensional spatial dimensions, in the case of an inhomogeneous plasma. The plasma density is under quarter-critical and depends linearly on the longitudinal spatial coordinate, in the regime where the Rosenbluth gain factor for the amplitude, denoted as G(Ros), is in the range pi/2< or =G_(Ros)< or =6. We observe that the Langmuir decay instability is able to suppress the gradient stabilization and restore the absolute nature of BSRS, thus leading to a significantly increased BSRS reflectivity. 相似文献
2.
Simulations are reported of the Thomson scatter spectrum of electrostatic waves (ESWs) excited in single laser hot spots by backward stimulated Raman scattering (BSRS). Under conditions similar those in the recent experiments of Kline et al. [Phys. Rev. Lett. 94, 175003 (2005)], a spectral streak, resulting from the trapping-induced frequency shift of the ESW, is found for high wave-number ESWs, similar to the observations. This shift and parametric frequency matching lead to isolated BSRS pulses. Modes with acoustic dispersion, resulting from the trapping-modified electron velocity distribution, can enhance the frequency range of the streak. 相似文献
3.
Montgomery DS Focia RJ Rose HA Russell DA Cobble JA Fernández JC Johnson RP 《Physical review letters》2001,87(15):155001
A diffraction-limited laser interacts with a plasma whose conditions are uniform on the scale of the focused laser spot. Two distinct, narrow waves are observed in the backscattered spectrum with phase velocities of v(phi)/v(e) = 1.4+/-0.08 and 4.2+/-0.1, where v(e) is the electron thermal speed. The high-velocity wave is ordinary stimulated Raman scattering (SRS) from a Langmuir wave. The low-velocity wave corresponds to stimulated scattering from an electron-acoustic wave (SEAS), and implies strong electron trapping. Previous SRS data from low-density plasmas are reinterpreted in terms of SEAS. 相似文献
4.
Chapman T Hüller S Masson-Laborde PE Heron A Pesme D Rozmus W 《Physical review letters》2012,108(14):145003
The autoresonant behavior of Langmuir waves excited by stimulated Raman scattering (SRS) is clearly identified in particle-in-cell (PIC) simulations in an inhomogeneous plasma. As previously shown via a 3-wave coupling model [T. Chapman et al., Phys. Plasmas 17, 122317 (2010)], weakly kinetic effects such as trapping can be described via an amplitude-dependent frequency shift that compensates the dephasing of the resonance of SRS due to the inhomogeneity. The autoresonance (AR) leads to phase locking and to growth of the Langmuir wave beyond the spatial amplification expected from Rosenbluth's model in an inhomogeneous profile [M. N. Rosenbluth, Phys. Rev. Lett. 29, 565 (1972)]. Results from PIC simulations and from a 3-wave coupling code show very good agreement, leading to the conclusion that AR arises even beyond the so-called weakly kinetic regime. 相似文献
5.
Z. Malá 《Czechoslovak Journal of Physics》2005,55(8):989-1003
This paper is devoted to the study of the nonlinear interaction of the waves generated by stimulated Raman scattering in plasma.
The influence of nonlinear interaction of plasma wave with plasma electrons on the sum of action densities of waves generated
by the laser wave is solved. The electron acceleration in the forward and backward wave fields is described. The change of
the electric field of the quasimode of forward and backward plasma waves of Raman scattering given by trapping of plasma particles
is calculated. Numerical results are calculated for typical parameters of the PALS experiment. 相似文献
6.
Asymmetry in the intensities between backward and forward stimulated Raman scattered radiations (BSRS and FSRS respectively)
in acetone is investigated in the presence of a fluorescing impurity (rhodamine 6G). In the case of pure acetone above a threshold
pump power, BSRS becomes more intense than FSRS. On the other hand intensity of BSRS decreases with concentration of the fluorophore
in solution, while that of FSRS is found to increase. It is observed that absorption saturation also affects the asymmetry
between FSRS and BSRS. 相似文献
7.
8.
为提高液体介质中受激拉曼散射的输出能量,提出了通过温度调控来抑制受激布里渊散射的方法,设计了532 nm多纵模宽带脉冲激光泵浦的受激拉曼散射发生系统,测量了不同温度下水中前向受激拉曼散射及后向受激布里渊散射的输出能量,分析了水温、泵浦激光线宽及热散焦效应对受激拉曼散射输出能量影响的物理机制.实验结果表明:通过降低水温可实现对受激布里渊散射过程的有效抑制,同时减小热散焦效应带来的光束畸变,从而有效提高受激拉曼散射的输出能量.研究结果对液体介质中的受激拉曼散射多波长转换具有重要意义. 相似文献
9.
M.?Ma?ek K.?Rohlena 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2010,56(1):79-90
The electron phase space evolution in a non-relativistic
and homogeneous laser plasma generated by a nanosecond laser in a
near infrared region in the presence of stimulated Raman scattering
is investigated by a numerical simulation. The mechanism of electron
acceleration in the potential wells of the plasma wave accompanying
the Raman back-scattering is analyzed in a 1D Vlasov-Maxwell model.
The dominant wave modes are both the backward and the forward
propagating Raman waves, each accompanied by a daughter
electrostatic wave. In addition to a strong interaction of plasma
electrons with the primary electrostatic wave in the case of
back-scattering, a cascading is observed consisting in a secondary
scattering of the primary Raman back-scattered wave. This phenomenon
reduces the Raman reflectivity and causes an acceleration of
electrons against the direction of the heating laser beam. Moreover,
the strong trapping in the primary electrostatic wave generated by
the Raman back-scattering leads due to the trapped particle
instability to a significant spectral broadening of the original
plasma wave and a subsequent intermittent behaviour of the
scattering process. The high phase velocity electrostatic daughter
wave of the forward Raman scattering cannot trap the electrons
directly, but there is an indication of non-resonant quasi-modes
combined of this wave and of the simultaneously existing
electrostatic daughter wave accompanying the Raman back-scattering.
The transform method is used for a solution of the set of partial
differential equations, which consists of the Vlasov equation and of
the full set of Maxwell equations in a 1D approximation. A
simplified Fokker-Planck collision term is added to overcome the
numerical instabilities during the simulation. The model has
relevance to a long scale plasma geometry, such as occurring in the
indirect drive experiments near the light entrance holes of target
hohlraum. 相似文献
10.
In the field of Brillouin lidar, it has very important significance to find one method that can amplify the Brillouin scattering signal in real time. One new-type Brillouin lidar detection system based on Nd:YAG pulsed laser and polarization control device is designed in this paper. The key point of this detection system is to have two pulsed coherent lights with same frequency, same polarization and same initial phase, of which one beam is taken as the detection wave for generating stimulated Brillouin scattering signal and the other beam is taken as pumping wave for real time and effective amplification of stimulated Brillouin scattering signal. This detection system mainly includes two pulsed lasers and one electro-optical polarization controller. The laser is mainly used to obtain the pulsed lights with same frequency and same phase, and the polarization controller is mainly used to change the polarization state of two coaxial beams to make them change into same polarization state from orthogonal polarization state thus to enable the pumping wave to amplify the backward stimulated Brillouin scattering signal. It is shown from the experimental results that the adoption of this new system can realize the effect of pumping amplification and can increase the signal to noise ratio to a certain extent. 相似文献
11.
在激光等离子体相互作用过程中,受激拉曼散射(SRS)会通过Langmuir波衰减不稳定性(LDI)和电子俘获两种机理饱和.文章给出均匀一维等离子体和低强度非相对论激光作用中,LDI和电子俘获两种机理下的SRS饱和时间的解析表达式.SRS饱和时间与入射激光强度,电子密度,电子温度,初始电子密度微扰等参数有关.解析理论计算得到了与模拟和实验相符的结果.
关键词:
受激拉曼散射
饱和
Langmuir波衰变不稳定性(LDI)
电子俘获 相似文献
12.
Depierreux S Fuchs J Labaune C Michard A Baldis HA Pesme D Huller S Laval G 《Physical review letters》2000,84(13):2869-2872
Thomson scattering measurements are presented which demonstrate conclusively the occurrence of the Langmuir decay instability (LDI) in a laser-produced plasma experiment. Both products of the instability, the ion acoustic wave and the electron plasma wave, were simultaneously observed and identified with their spectral characteristics. The secondary decay of the LDI-generated electron plasma wave, into another Langmuir wave and an ion acoustic wave, has been observed for the first time. The connection with growth and saturation of the stimulated Raman instability is discussed. 相似文献
13.
14.
J. Shi X. Chen M. Ouyang W. Gong Y. Su D. Liu 《Applied physics. B, Lasers and optics》2012,106(2):445-451
The pumping effect of stimulated Brillouin scattering on stimulated Raman scattering is investigated theoretically through
the coupled wave equations of stimulated Brillouin scattering and stimulated Raman scattering. The numerical simulations are
in agreement with the experimental results. They indicate that the backward stimulated Raman scattering is excited and amplified
collectively by both pump laser and stimulated Brillouin scattering. 相似文献
15.
B. S. Sharma N. K. Jaiman 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,48(1):83-86
A nonlocal theory of stimulated Raman backscattering (BSRS) parametric instability of a large amplitude electromagnetic (EM)
mode in a strongly magnetized plasma e.g., one encountered in a plasma filled backward wave oscillator, is reported. The EM
mode is unstable to parametric instability in a magnetized plasma and decays into a Trivelpiece-Gould (TG) mode and a sideband
EM mode. The growth rate of instability (Γ) scales proportional to three-fourth power of plasma density. For a typical BWO
the growth rate is ∼108 s-1 相似文献
16.
M. V. Starodubtsev V. V. Nazarov A. V. Kostrov 《Radiophysics and Quantum Electronics》2009,52(11):796-809
We present the results of laboratory studies of the formation of a number of spectral components of stimulated electromagnetic
emission, which are related to the excitation of small-scale irregularities in the heated ionosphere. In the laboratory experiment,
the small-scale irregularity was formed as a result of thermal self-channeling of short-wavelength quasielectrostatic oscillations
in a magnetoplasma. Using the method of probing waves, it is experimentally shown that the trapping and waveguide propagation
in a small-scale plasma irregularity are exclusively due to Langmuir waves, whereas the upper-hybrid waves with anomalous
dispersion are not trapped into the irregularity. It is found that satellites shifted by about 1–2 MHz from the carrier frequency
(700 MHz under the experimental conditions) are formed in the Langmuir wave spectrum during the thermal self-channeling. Two
mechanisms of generation of spectral satellites have been detected. The first (dynamic) mechanism is observed during the formation
of a small-scale irregularity with rapidly increasing longitudinal size. In this case, one low-frequency satellite is excited
in the trapped-wave spectrum. The mechanism of the formation of this satellite is apparently related to the Doppler shift
of the frequency of the Langmuir waves trapped inside the irregularity. The second (stationary) mechanism is observed in the
case of a developed irregularity where its shape is close to cylindrical. In this regime, the trapped-wave spectrum has two
symmetric spectral satellites, namely, high- and low-frequency ones. It may be hypothesized that the generation of these satellites
is due to scattering of trapped Langmuir waves from drift oscillations of the irregularity. 相似文献
17.
基于电子与多光子集团非线性Compton散射模型,研究了多光子非线性Compton散射对激光等离子体中强缪尔湍动谱的影响,提出了将入射光和散射光作为形成强缪尔湍动的新机制,给出了横等离激元、强朗缪尔激元和离声激元之间相互作用满足的修正方程,并进行了数值模拟.结果表明:Compton散射使横等离激元和朗缪尔激元间的碰撞频率大大增加,随着时间的演化,横等离激元和朗缪尔激元的能量由小波数区向大波数区的转移比散射前要快得多,同时产生剧烈的坍塌.坍塌后期,等离激元的强非线性作用激发出高次共振谐波,使能量从一个谐波转移到另一个谐波,形成无限高次谐波,引起波的破碎,出现由调制不稳定性控制的强朗缪尔湍动、较强的激光成丝和能量均分现象.研究结果为进一步研究强朗缪尔湍动的加速机制、反常碰撞、激光加热实验及快点火实验提供了理论支持. 相似文献
18.
Evolution of a Langmuir wave is studied numerically for finite amplitudes slightly above the threshold which separates damping from nondamping cases. Arrest of linear damping is found to be a second-order effect due to ballistic evolution of perturbations, resonant power transfer between field and particles, and organization of phase space into a positive slope for the average distribution function f(av) around the resonant wave phase speed nu(ph). Near the threshold trapping in the wave potential does not arrest damping or saturate the subsequent growth phase. 相似文献
19.
Kline JL Montgomery DS Bezzerides B Cobble JA DuBois DF Johnson RP Rose HA Yin L Vu HX 《Physical review letters》2005,94(17):175003
Thomson scattering is used to measure Langmuir waves (LW) driven by stimulated Raman scattering (SRS) in a diffraction limited laser focal spot. For SRS at wave numbers klambda(D) less similar 0.29, where k is the LW number and lambda(D) is the Debye length, multiple waves are detected and are attributed to the Langmuir decay instability (LDI) driven by the primary LW. At klambda(D) greater similar 0.29, a single wave, frequency-broadened spectrum is observed. The transition from the fluid to the kinetic regime is qualitatively consistent with particle-in-cell simulations and crossing of the LDI amplitude threshold above that for LW self-focusing. 相似文献
20.
Using bosonization and phase shift representation, we rigorously treat backward scattering of electrons on an impurity in a one-dimensional interacting electronic system, and demonstrate that correlation exponents of the system depend on a phase shift induced by the backward scattering, and usual exponent duality of the correlation functions between ultraviolet and infrared fixed points comes from the phase shift dependence of the correlation exponents. Finally, we study the tunnelling conductance of the system at zero temperature and obtain a modified Landauer-Bütiker formula. 相似文献