首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 146 毫秒
1.
研究了红外频段非线性s偏振表面波在反铁磁晶体和电介质交界面上的频率特性,求出了非线性色散方程,揭示了非线性s偏振表面波存在一个临界频率,低于这个频率,非线性s偏振表面波的频率范围,发现功率不再是决定导波频率范围的唯一因素,两种材料的介电常数比在这里起了至关重要的作用。  相似文献   

2.
采用分布傅立叶方法数值模拟了飞秒光脉冲在光子晶体光纤反常色散区的非线性传输和压缩过程。计算和分析了不同泵浦波长对光子晶体光纤中超短脉冲传输和压缩的影响,结果表明,在相同初始脉冲峰值功率条件下,泵浦波长为1000nm的脉冲压缩因子和峰值功率最大,最佳光纤长度最短,但品质因子适中,并且随着初始峰值的增大,其压缩因子增长幅度最大。合理选择泵浦波长,有利于增强压缩效果,提高脉冲压缩质量和峰值功率,使得最佳光纤长度减小。  相似文献   

3.
饱和非线性光纤正色散区的交叉相位调制不稳定性   总被引:1,自引:0,他引:1  
钟先琼  向安平 《中国激光》2006,33(3):35-338
在考虑到光纤饱和非线性效应的情况下,给出了同偏振、不同波长的两光波的慢变振幅满足的耦合非线性薛定谔方程组以及线性化后微扰满足的方程组。在光纤的正色散区,分析并讨论了交叉相位调制不稳定增益谱随两光波输入功率变化的规律。结果表明,与饱和非线性光纤中自相位调制不稳定性的增益谱类似,交叉相位调制不稳定增益谱的临界扰动频率、峰值增益大小随两光波输入功率的增大也呈现出先增大后减小的特点,而二者随两光波输入功率变化的快慢都与两扰动的频率大小有关,即会出现两个不同的输入功率对应同一个不稳定增益峰值和临界扰动频率的情形。  相似文献   

4.
研究了反铁磁和超晶格界面上非线性TM表面波的传播特性,发现超晶格体中液晶层晶轴取向θ为0或π/2时非线性TM表面波才能在所讨论的界面上存在,导出了非线性TM表面波的色散关系,分析了非线性TM表面波的频率特性  相似文献   

5.
应用多光子非线性Compton散射模型,对Compton散射下的3阶色散对超短光孤子脉冲自频移的影响进行了研究,通过理论分析、数值模拟和拟合,结果表明,Compton散射使3阶色散对孤子自频移有较强的抑制作用,在时域中引起孤子脉冲的调制振荡结构更为明显,频域中的频谱被分为两个较清晰的、峰值较高的谱峰,孤子自频移 ,但其斜率不同于散射前的斜率。  相似文献   

6.
为了实现在纵向变化的参量控制下,(2+1)维空间光孤子不稳定性的抑制,通过了数值地求解变系数的(2+1)维非线性薛定谔方程,讨论了在参量控制下的(2+1)维空间光孤子。结果发现,一定的参量控制,即沿传播方向周期性改变的衍射参量和自聚焦效应参量可有效抑制(2+1)维空间光孤子的不稳定性。另外,进一步的数值计算表明,在一定参量控制下的(2+1)维空间光孤子的传输对损耗,有限的扰动,如白噪声等不敏感。 这表明参量控制的(2+1)维空间光孤子应该是稳定的。  相似文献   

7.
用磁性异向介质抑制共面天线间的表面波   总被引:1,自引:0,他引:1  
从电磁波传播原理上说明可用磁性异向介质抑制舰载共面相控阵天线间的表面波,利用时域有限积分法在CST Microwave Studio中对理想导电体(Perfect Electric Conductor,PEC)平面上两个天线端口的仿真模型进行全波求解计算,结果表明:磁性异向介质不但可以在等效磁导率实部为负的频段内增大天线间的隔离度,而且在某些频率还能降低阵面天线模型的后向散射值,并分析了异向介质厚度的变化对电磁兼容性和整体隐身性的影响,异向介质厚度的选择与其电磁本构参数的确定同等重要.  相似文献   

8.
研究了电磁波对等离子体进行加热所产生的非线性效应,分析了电磁波在等离子体中传播的热致非线性衰减,通过与线性衰减的计算结果进行比较,指出当电磁波频率较低且传输距离较远时线性计算产生较大误差,必须考虑电子温度升高引起的非线性衰减,并且分析了非线性衰减随频率、入射电波场强、传输距离等的变化关系,指出在一定条件下,电波对等离子体的加热可使电波的非线性衰减小于线性衰减。  相似文献   

9.
我们知道,激光平面波通过具有瞬时非线性的介质时,它的位相变化为:其中ω_L为激光频率;n_o为介质折射率;n_2为介质非线性折射系数;I_L(t)为激光强度;z为介质长度;c为光速。 相应引起瞬时激光频率变化为:对于泵浦激光来说,在光强最大值处即没有频率变化。在激光脉冲前沿频率移动为负,而在脉冲后沿频率移动为正。即激光在非线性介质中传播时,只存在位相调制,而最大值处频率没有移动。这种情况对于稳态和瞬态都是一样的。然而,斯托克斯场则不同,在稳态情况其最大值处没有频移,而脉冲前、后沿的频率移动大于激光瞬时频移的1.67倍。在瞬态情况,由于斯托克斯光峰值相对于激光峰值延迟约t_D=t_P/2。根据瞬态受激喇曼散射理论可求出斯托克斯光的瞬时频率为:  相似文献   

10.
在三五阶非线性共存时,研究了有损耗单模光纤中基于两光波交叉相位调制的不稳定条件和增益谱.在色散缓变光纤正色散区,分析了五阶非线性系数、色散纵向变化参量以及两扰动的频率大小关系对交叉相位调制不稳定增益谱的影响.结果表明,在五阶非线性下,色散的纵向渐减仍有利于展宽调制不稳定增益谱;正五阶非线性可使增益谱的谱宽和谱峰值增大,并使谱峰位置远离主波频率,负五阶非线性的作用则相反;两扰动频率大小关系不同,色散纵向参量的变化对增益谱的谱峰大小和位置的影响也不同,五阶非线性对交叉相位调制不稳定性的加强或抑制程度也不同.  相似文献   

11.
General conditions for the existence of plane electromagnetic waves with a single nonzero electric-field component (TE waves) in an anisotropic medium are established. A transformation that makes it possible to derive similar formulas for TM waves (plane electromagnetic waves with a single nonzero magnetic-field component) from the formulas expressing the properties of TE waves is considered. A general numerical algorithm is developed for calculating the amplitudes (with allowance for phases) of the TE waves formed when an external TE wave propagates through a system of plane-parallel plates consisting of media supporting TE waves. Formulas are obtained for the solution of the particular problem on the transmission of a TE wave through a plane interface between two media supporting TE waves. A series of relationships that can be interpreted as generalizations of the Snell and Fresnel relationships for media of the considered type are derived. Formulas for the transmission, reflection, and refraction coefficients are obtained. The existence conditions for TE (TM) surface waves are derived. A numerical method is proposed for computing the spectra of such surface waves formed on the interface between two media. For isotropic media, analytic expressions for the spectra of surface waves are derived. It is shown that the obtained formulas are similar to the known formulas for surface TM waves in dielectrics but, in addition, make it possible to take into account both the permittivities and permeabilities of the media.  相似文献   

12.
Dispersion of ground-penetrating radar (GPR) waves can occur when they are trapped in a layer. In this paper, we analyze the modal propagation of GPR pulses through a layer of ice that is overlying water. Dispersed transverse electric (TE) waves that are trapped in the waveguide have larger amplitudes than the critically refracted waves that travel through air, whereas the transverse magnetic (TM) critically refracted waves traveling through air are more dominant than the trapped dispersed TM waves. This can be explained by the leaky waveguide behavior of the ice layer. The reflection coefficients for the waves incident on the ice-water interface show that the TM modes are more leaky than the TE modes. Still, clear dispersion is observed in both cases, which depends on the permittivity and thickness of the ice. Similar to inversion of dispersed Rayleigh waves, these parameters can be estimated by calculating phase-velocity spectra, picking dispersion curves, and inverting the dispersion curves using a combined local and global minimization procedure. Synthetic data show several higher order modes of which separate and combined inversions return the input modeling parameters accurately. Experimental data acquired on a frozen lake show strong dispersion for the TE and TM modes. The phase-velocity spectra of the field data show three TE and four TM modes of which separate and combined inversion of different modes return similar values for the ice thickness and known permittivity of ice. Due to the more leaky behavior of the TM modes, the TE inversion is better constrained and more suitable for inversion.  相似文献   

13.
The reflection and the scattering properties of even TE and TM surface waves incident in an abruptly ended dielectric slab waveguide are analyzed. The discontinuity is regarded as a junction between two open waveguides namely the dielectric slab waveguide and the free space waveguide. The boundary conditions acting together with the orthogonality provide singular coupled integral equations on the discrete and the continuous wave amplitudes at the discontinuity. These singular coupled intergral equations with Cauchy kernels and infinite limits of integration are solved by iteration via the Neuman series. Numerical results are presented for the reflectivity of the even TE/sub 0/ and TM/sub 0/ fundamental modes, together with their mode conversion on even TE/sub 2/ and TM/sub 2/ in a slab where two guided modes can propagate. Reflectivity and mode conversion of higher order excitations are also investigated  相似文献   

14.
量子棒中强耦合磁极化子的振动频率   总被引:2,自引:2,他引:0  
给出了具有椭球边界量子棒经过坐标变换成球形边界的哈密顿量。采用线性组合算符和幺正变换的方法研究了在非均匀抛物限制势下量子棒中强耦合磁极化子的性质。导出了量子棒中强耦合磁极化子的振动频率和声子平均数随磁场的回旋频率、电子-声子耦合强度、椭球的纵横比和横向和纵向有效受限长度的变化关系。数值计算结果表明:振动频率和声子平均数随电子-声子耦合强度和磁场的回旋频率的增加而增加,随横向和纵向有效受限长度的减小而迅速增大。当 时,振动频率和声子平均数随椭球的纵横比的增加而增加。 时,随着椭球的纵横比的减少,振动频率和声子平均数都增大。当 时,振动频率和声子平均数取极小值。  相似文献   

15.
由电磁场的波动方程和边界条件建立了单负材料作为芯层的对称三层平板波导的模式本征方程,用图解法研究其色散特性。研究发现,单负介质波导不支持快波的传播,只支持表面波的传播。在负磁材料平板波导中只存在TE表面模,不存在TM表面模。分析了在负磁材料平板波导中TE模受磁导率的比值-μ2/μ1和波导参数的影响,给出了横向场分布图。在-μ2/μ1〈1时,偶对称只有TE0表面模存在,奇对称只有TE1表面模存在,高阶模式并不存在,且两种模式都没有低频截止;-μ2/μ1〉1时,TE1表面模始终不出现;TE0模的存在与否和波导参数有关,在一定条件下TE0模可出现双模并存。给出的结果可望对表面波器件的设计提供理论基础。  相似文献   

16.
The reflection and transmission properties of plane waves on the interface of uniaxial chiral media with the optical axis parallel to the interface are investigated. The formulas of the reflected and transmitted power are derived. The curves of the group refractive angles, power of the reflected and transmitted waves for TE and TM incident waves are presented for three cases of dielectric constant combinations and for non-chiral, weak chiral and strong chiral media. Some new results are obtained, which are different from those in the uniaxial chiral media with the optical axis per-pendicular to the interface.  相似文献   

17.
SrAl2O4 :Eu2+和SrAl2O4 :Eu2+,Dy3+长余辉和热释光谱   总被引:1,自引:0,他引:1  
对比研究了SrAl2O4:Eu2+和SrAl2O4:Eu2+,Dy3+的余辉特性和热释光谱,并探讨了Dy3+的掺杂对SrAl2O4:Eu2+陷阱能级的影响。XRD晶相分析表明: Eu2+和Dy3+的掺杂并没有改变SrAl2O4的晶体结构。发光分析表明:Dy3+的掺杂没有改变SrAl2O4:Eu2+的光致发光光谱和发光中心。热释光谱对比分析结果显示:Eu2+的掺杂在SrAl2O4的禁带中引入了两个深度不同的陷阱能级;Dy3+的掺杂并不改变原来陷阱能级的深度,却能够显著地增加原来浅陷阱能级的密度,从而改善了SrAl2O4:Eu2+的余辉特性。不同等待时间的热释光谱曲线显示:在室温下,不同陷阱能级衰减规律的差异以及陷阱能级间存在的电子转移,可能造成了SrAl2O4:Eu2+,Dy3+长余辉材料复杂的余辉衰减规律。  相似文献   

18.
考虑由左手系材料作覆层衬底的对称波导系统,研究了TE线性极化波在该波导中的传播特性.利用直接图解法对各种波导模式进行了详细地判别,结果表明快波、慢波均可以在该波导中传播,两者的模式特征与传统介电波导及左手波导均存在较大差异.分析了导波的色散关系并定性地讨论了群速度随频率的变化规律.揭示了在一定条件下,该波导系统既可以支持前向线性TE波的传播也可以支持反向线性TE波的传播,且支持低阶快波偶模式和慢波奇模式传播的频率段相对狭窄.  相似文献   

19.
Recently, the concept of chirowaveguides, which exhibit some novel and interesting properties due to electromagnetic chirality, was introduced and studied elsewhere. In this paper, the authors analyze theoretically another problem associated with chirowaveguides, namely, the problem of reflection and transmission of guided waves at an air-chiral interface and at a chiral slab located transversely in a parallel-plate waveguide. The notable features and the role of chirality of the medium on the reflected and transmitted guided waves are discussed, and physical insights into these results are provided. It is found that since the guided modes inside the chiral region of the waveguide are hybrid, in order to satisfy the boundary conditions at interfaces, the reflected and transmitted guided modes in the air regions of the waveguides need to be of TE and TM modes. The motivation behind this study is the potential applications of this problem to the design of novel measurement techniques for determining material parameters of chiral composites  相似文献   

20.
Complex geological structures are modelled in the presence of an air-Earth interface. A cross-borehole configuration of target, source, and receiver is assumed, with the target itself not restricted as to geometrical cross section or complex permittivity value. Two-dimensional method-of-moment formulations are employed, utilizing cylindrical pulse basis functions and point matching. Scattering from buried dielectric objects is computed near the air-Earth interface for both TE and TM incident fields. A Sommerfeld-Green function is used to represent the effect of the air-Earth interface on the incident fields and the impedance matrix. The TE case is examined for scattering of both the copolarized and cross-polarized electric fields, and several examples are given for a cylindrical target at depths that vary from one to twenty four wavelengths, after which the presence of the air-Earth interface can be neglected. Some experimental results utilizing a 1/40th laboratory scale model and a tunnel-like target are also included for comparison. The technique enables the user to investigate electromagnetic scattering from a variety of complex buried objects whose dimensions are typically in or below the resonance region. The simultaneous relaxation of restrictions on cross section, material properties, and burial depth, together with experimental validation, is not found in the literature to date  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