共查询到20条相似文献,搜索用时 31 毫秒
1.
In a biased photorefractive crystal, the process of two
one-dimensional waves mixing, i.e., the dynamical evolution of
both pump beam and signal beam, is traced by numerically solving the
coupled-wave equation. Direct simulations show that the
propagation and stability of the two beams are completely determined
by the system parameters, such as the external bias field, the
intensity and the beam waist of the pump beam. By adjusting these
parameters, one can control the state of two Gaussian waves mixing.
The numerical results are helpful for performing a two-wave mixing
experiment. 相似文献
2.
E. Jakeman 《Waves in Random and Complex Media》1991,1(3):S109-S119
In calculating the properties of waves scattered by random media it is almost always assumed that variations of the media constitute a joint Gaussian process. In this paper two alternative models are investigated. It is shown that whilst some features of the statistics of the scattered waves are more sensitive to the spectrum of the fluctuations in the medium than to the basic statistical model, in general significantly different properties are predicted using the alternative models. 相似文献
3.
《Waves in Random and Complex Media》2013,23(4):729-745
The Gauss–Lagrange model for ocean waves describes the vertical and horizontal movements of water particles as three correlated Gaussian fields. The model can produce irregular waves, asymmetric in both vertical and horizontal direction, and by judicious choice of a single skewness parameter the front–back asymmetry can be regulated to realistic values. In this paper, it is shown that this additive model for shallow waters can also produce horseshoe-like patterns around moderate to high wave crests. Such phenomena are usually analyzed and described as nonlinear interaction effects between different frequencies. The tool in the paper is a Slepian model for the three-dimensional movements conditioned on a wave crest 相似文献
4.
《Waves in Random and Complex Media》2013,23(3):S109-S119
Abstract In calculating the properties of waves scattered by random media it is almost always assumed that variations of the media constitute a joint Gaussian process. In this paper two alternative models are investigated. It is shown that whilst some features of the statistics of the scattered waves are more sensitive to the spectrum of the fluctuations in the medium than to the basic statistical model, in general significantly different properties are predicted using the alternative models. 相似文献
5.
B. Borasoy E. Epelbaum H. Krebs D. Lee U. -G. Meißner 《The European Physical Journal A - Hadrons and Nuclei》2007,34(2):185-196
We determine two-particle scattering phase shifts and mixing angles for quantum theories defined with lattice regularization.
The method is suitable for any non-relativistic effective theory of point particles on the lattice. In the center-of-mass
frame of the two-particle system we impose a hard spherical wall at some fixed large radius. For channels without partial-wave
mixing the partial-wave phase shifts are determined from the energies of the nearly spherical standing waves. For channels
with partial-wave mixing further information is extracted by decomposing the standing wave at the wall boundary into spherical
harmonics, and we solve coupled-channels equations to extract the phase shifts and mixing angles. The method is illustrated
and tested by computing phase shifts and mixing angles on the lattice for spin-1/2 particles with an attractive Gaussian potential
containing both central and tensor force parts. 相似文献
6.
We present two flexible stochastic models for 2D and 3D ocean waves with potential to reproduce severe and non-homogeneous
sea conditions. The first family consists of generalized Lagrange models for the movements of individual water particles.
These models can generate crest-trough and front-back statistically asymmetric waves, with the same degree of asymmetry as
measured ocean waves. They are still in the Gaussian family and it is possible to calculate different slope distributions
exactly from a wave energy spectrum. The second model is a random field model that is generated by a system of nested stochastic
partial differential equations. This model can be adapted to spatially non-homogeneous sea conditions and it can approximate
standard wave spectra. One advantage with this model is that Hilbert space approximations can be used to obtain computationally
efficient representations with Markov-type properties that facilitate the use of sparse matrix techniques in simulation and
estimation. 相似文献
7.
Cheng-Shi Liu 《理论物理通讯》2021,73(4):45007
In the paper, we try to study the mechanism of the existence of Gaussian waves in high degree logarithmic nonlinear wave motions. We first construct two model equations which include the high order dispersion and a second degree logarithmic nonlinearity. And then we prove that the Gaussian waves can exist for high degree logarithmic nonlinear wave equations if the balance between the dispersion and logarithmic nonlinearity is kept. Our mathematical tool is the logarithmic trial equation method. 相似文献
8.
In this paper, a fractional photon model is proposed by considering the photon-exchange interaction in the reverse process of the non-linear three-photon mixing interaction. The phase matching condition for various types of uniaxial crystals can be simplified and classified by this model with the consideration of the unequal fractional photon-exchange of the two generated waves in the reverse manner. This also leads to the explanation of observing the phase mismatch and output bandwidth of the resonant and non-resonant waves in a cavity. Finally, a quantitative approach to this model, with experimental results, is also demonstrated. 相似文献
9.
在傍轴近似条件下建立了OPO的数学模型,通过引入三波混频中时间与空间关系,采用分步傅里叶算法模拟了纳秒级脉冲和连续光波在谐振腔内的三波混频过程。理论模型中考虑了不同频率光波之间的色散关系,可以在高转换效率情况下分析不同泵浦脉冲功率、脉冲时长、腔镜透反射比以及不同种子光输入等情况下的输出波形、功率以及OPO阈值等特性。实验中采用掺杂MgO的周期性极化铌酸锂晶体(MgO∶PPLN)为非线性介质,在输入1.06 m泵浦激光脉冲能量为0.4 mJ时,产生3.8 m闲频光超过0.07 mJ输出,与数值模拟结果0.08 mJ较为符合。 相似文献
10.
It is shown that it is possible to increase dramatically the efficiency of stationary four-wave mixing in cubic photorefractive crystals of the sillenite family. In order to do this one has to use a holographic arrangement of the cubic crystal where the same volume phase hologram has opposite contrasts for orthogonally polarized light waves traversing the sample in opposite directions. In combination with a new efficient nonstationary mechanism of shifted hologram formation, this arrangement can enable phase conjugation of amplified waves and stationary selfoscillation without an external resonator cavity. 相似文献
11.
四波混频作为一种噪声广泛存在于各种光放大器中,论文将对TDM泵浦方式的拉曼放大器的四波混频噪声进行分析和仿真,最后提出改善四波混频噪声的方法。 相似文献
12.
In this paper, we studied the effect of Gaussian coloured noise on
the formation and instability of spiral waves described by one class
of modified FitzHugh--Nagumo equation. It was found that Gaussian
coloured noise plays a constructive role in the formation,
transition and instability of spiral wave. Too weak or too strong
noise may act against the formation of spiral waves. At a certain
noise level, spiral wave is maintained in a medium, in which spiral
wave cannot be observed in the absence of the noise. It is difficult
to make a stable spiral wave into unstable state by Gaussian
coloured noise, unless the noise level is very high. The parameter
regions of Gaussian coloured noise for spiral forming and spiral
instability were given and discussed with numerical simulations. 相似文献
13.
Spatial coherence resonance induced by coloured noise and parameter diversity in a neuronal network 下载免费PDF全文
Spatial coherence resonance in a two-dimensional neuronal network
induced by additive Gaussian coloured noise and parameter diversity
is studied. We focus on the ability of additive Gaussian coloured
noise and parameter diversity to extract a particular spatial
frequency (wave number) of excitatory waves in the excitable medium
of this network. We show that there exists an intermediate noise
level of the coloured noise and a particular value of diversity,
where a characteristic spatial frequency of the system comes forth.
Hereby, it is verified that spatial coherence resonance occurs in
the studied model. Furthermore, we show that the optimal noise
intensity for spatial coherence resonance decays exponentially with
respect to the noise correlation time. Some explanations of the
observed nonlinear phenomena are also presented. 相似文献
14.
We reveal a mechanism of resonant excitation of non-dispersive coastal Kelvin waves by pairs of incident/reflected inertia-gravity waves in the rotating stratified fluid. In the simplest rotating shallow water model on the semi-infinite plane we show that the mechanism works for a continuum of incoming waves, and thus should be ubiquitous in the ocean. Subsequent slow evolution of thus excited Kelvin waves is governed by harmonically forced simple-wave equation and leads to nontrivial transport and mixing properties. 相似文献
15.
S. Van den Bulcke L. Zhang A. Franchois J. M. Geffrin J. Stiens 《International Journal of Infrared and Millimeter Waves》2008,29(11):1038-1047
For the development of millimeter wave imaging systems, it is important to be able to simulate some representative scattering
configurations. Typically, Gaussian beams are used in active imaging systems. Since these beams only illuminate a spatially
limited region, many objects can be treated as infinitely long 2D (in)homogenous cylinders. However, the incident Gaussian
beams have a 3D character. Therefore, a dedicated 2.5D scattering simulator was developed. In this paper, simulation results
obtained with this simulator are compared to measurements obtained from a bi-static microwave set-up and from a W-band millimeter
wave set-up. Comparison of simulations and measurements proves that the 2.5D algorithm is a good simulation tool to study
scattering of long inhomogeneous cylinders, illuminated by 3D plane waves or 3D Gaussian beams under different elevation angles. 相似文献
16.
The theoretical conversion of the Bessel-modulated Gaussian beam with a quadratic radial dependence by a spiral phase plate (SPP) leads us to generate a novel donut family that we called it Humbert beam. In this paper, the different theoretical tools are developed to obtain these new waves. Some numerical calculations are performed to study the transformation and the propagation of this new family by a SPP with an integer topological charge through an ABCD optical system. The present study shows also that the Humbert beam generalized the Kummer family waves. 相似文献
17.
The breaking of longitudinal Akhiezer-Polovin (AP) waves is demonstrated using a one-dimensional simulation based on the Dawson sheet model. It is found that the AP longitudinal waves break through the process of phase mixing at an amplitude well below the breaking amplitude for AP waves, when subjected to arbitrarily small longitudinal perturbations. Results from the simulation show a good agreement with the Dawson phase mixing formula modified to include relativistic mass variation effects. This result may be of direct relevance to the laser- or particle-beam plasma wakefield experiments. 相似文献
18.
采用概率统计方法——蒙特卡罗方法,建立一种预测液固两相体系中混合弹性球形颗粒声衰减的理论模型。在单颗粒声散射和吸收的基础上,将连续超声波抽象离散化为大量独立的声子,追踪声散射过程,通过统计接收器探测声子数最终确定声衰减系数。采用数值方法对单一球形颗粒的液固两相体系中声衰减进行预测和比较,确定了该方法的可行性后将该方法推广到混合颗粒体系中,对玻璃微珠/铁粉构成的混合颗粒及多分散混合颗粒体系进行数值研究。结果表明:在体积浓度低于10%时,蒙特卡罗法预测得玻璃微珠或铁粉颗粒声衰减和ECAH,Lloyd和Berry,Waterman等建立的模型结果吻合。对于混合颗粒构成的两相体系,算例中,随着体积浓度增大到10%,声衰减系数随混合颗粒数目比的变化呈现出了非线性的变化,同时颗粒物性也会影响不同组分颗粒对声衰减的贡献,算例中铁粉颗粒比玻璃微珠对声衰减的影响更大。 相似文献
19.
In this paper, a 120-fs pulse transmission experiment is carried out using disordered birefringent microstructure fibers with cladding ventages. Through this experiment, it is found for the first time that remarkable Stokes and anti-Stokes waves can also be produced when the central wavelength of the incident pulse is in the normal dispersion regime of the microstructure fiber. The generation of the two waves can be explained by the four-wave mixing phase matching theory. Properties of the two waves under the action of femtosecond laser pulses with different parameters are studied. The results show that the central wavelength of anti-Stokes waves and Stokes waves produced under the two orthogonal polarization states shift by 63 nm and 160 nm, respectively. The strengths and central positions of the two waves in birefringent fibers can be controlled by adjusting the phase match condition and the polarization directions of incident pulses. 相似文献
20.
It is well known, [1–6], that the linearized equations of motion of ideal MHD possess a continuous spectrum which leads to damping of propagating waves through phase mixing. We show how this arises by examining the dispersion relation for plasmas with non-uniform profiles and comparing the results with those of a sharp boundary model. In this paper the special case of the non-uniform sheet-pinch is examined in order to present the mathematical details as clearly as possible. It is shown that as a result of the non-uniformity the frequency of the waves is a complex quantity having a real and imaginary part. The corresponding eigenfunctions and their mathematical pathology are discussed. 相似文献