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为了从理论上统一射线光学和导波光学关于多模光纤中各模式场传播过程中时延的论述,试从介质波导理论出发,根据模式的特征根U随光纤归一化频率R的变化关系,在弱波导近似下导出了描述模式场相速Vp与群速Vg关系的重要结果:Vp*Vg=(c/n1)2。根据这一结果可以得出结论:对于低阶模式,由于相速Vp慢,所以群速快;高阶模式其相速Vp快,所以群速慢。对于给定的光纤,利用射线光学和波导光学进行了带宽估计,2种理论计算结果的一致性,印证了上述关系的正确性。 相似文献
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色散、群速与群折射率 总被引:1,自引:2,他引:1
本文讨论了群折射率存在的物理意义,指出群折射率不仅包含了折射率概念而且还体现了折射率的色散性质,同样能作为材料本身的光学性质参量.接着指出在折射率的白光干涉法测量中存在着忽视色散作用而导致的将群折射率误认为折射率的情况.将群折射率与折射率区别开来,不仅可以消除折射率测量中所存在的错误,而且可以突出色散现象在光传播时间特性上的意义.为此建立了折射率与群折射率的相互变换关系,通过对于典型物质的折射率与群折射率变换关系的计算,说明二者在数值上的差别甚至对于气体介质来说也是不能忽略的. 相似文献
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在光纤零群速色散区传输的光孤子波 总被引:1,自引:0,他引:1
通过对超短光脉冲在单模光纤中传输方程的分析研究,给出了在零群速色散传输方程的亮,反波解。结果表明,超短光脉中在光纤的零群群速色散仍能以亮,暗孤波的形式传输,且不存在孤子自频移现象。 相似文献
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通过对PPQ薄膜的吸收光学谱的计算分析,由Kramers-Kronig关系得到PPQ膜在550nm~700nm左右波段存在负群速色散区,并且色散量对相对较小,│β2│〉1.2ps^2/m,这使得对飞秒激光脉冲在PPQ平面光波导中的传输的传输的描述可以忽略色散顶,根据这一间化,仅考虑自相位调制(SPM)效应,由于飞秒对撞锁激光脉冲的光谱展宽民计算的PPQ的非线性折射率系数n2,与报道的结果吻合很好。 相似文献
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In anisotropic media, the direction of energy propagation does not necessarily coincide with the wave normal, i.e. the energy flux vector does not coincide with the wave normal. Since, experimentally, one measures group velocity not phase velocity, one must therefore be careful in interpreting ultrasonic wave speed measurements in anisotropic media. This is of particular importance in elastic property reconstruction where acoustic velocity measurements are used as the basis for determining anisotropic material properties. In this work, the consequences of energy flux deviation from the wave normal are considered for typical experimental geometries. Particular attention is devoted to developing appropriate relationships between the phase velocity and ultrasonic transit time measurements, as these relations are most useful for elastic property reconstruction. In all the cases considered, it is shown that the phase velocity can be directly calculated from appropriate time delay measurements. 相似文献
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Abstract The velocity of longitudinal ultrasonic waves, ν1,(P), in polycrystalline cesium was measured at 293 ±1K in the pressure interval 0–5 GPa. v 1(P) alterations at BCC-FCC phase transition at 2.3 GPa and at the electronic-structure transformation at 4.3 GPa were obtained. Decrease of v 1(P) to 4.3 GPa after a maximum at ~3.8 GPa were found, that gave evidence to the appearance of a corresponding soft mode in the FCC-Cs phonon spectrum. The peculiarities of dependence v 1(P) correlate with s-conduction electrons promotion to the empty d-band in accordance with the theoretically predicted continuous electronic s-d transformation in Cs. 相似文献
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理论上分析了超声光栅衍射和液体表面波光栅衍射,得到了表面波光栅衍射图样与表面波参数的解析关系.实验上得到清晰的衍射图样,利用表面波光栅衍射法测量了液体表面波波速,实验结果与理论值误差不超过1%. 相似文献
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Review on second-harmonic generation of ultrasonic guided waves in solid media (I):Theoretical analyses 下载免费PDF全文
Considering the high sensitivity of the nonlinear ultrasonic measurement technique and great advantages of the guided wave testing method, the use of nonlinear ultrasonic guided waves provides a promising means for evaluating and characterizing the hidden and/or inaccessible damage/degradation in solid media. Increasing attention on the development of the testing method based on nonlinear ultrasonic guided waves is largely attributed to the theoretical advances of nonlinear guided waves propagation in solid media. One of the typical acoustic nonlinear responses is the generation of second harmonics that can be used to effectively evaluate damage/degradation in materials/structures. In this paper, the theoretical progress of second-harmonic generation (SHG) of ultrasonic guided wave propagation in solid media is reviewed. The advances and developments of theoretical investigations on the effect of SHG of ultrasonic guided wave propagation in different structures are addressed. Some obscure understandings and the ideas in dispute are also discussed. 相似文献
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Ultrasonic velocity, density and viscosity were measured in two ternary liquid systems namely,n-pentane +n-hexane + benzene(I) andn-hexane + cyclohexane + benzene(II) and one quaternary liquid system,n-pentane +n-hexane + benzene + toluene (III). The experimental as well as literature values of thermal expansion coefficient and iso-thermal
compressibility of pure liquid components were utilized to deduce the ideal value of internal pressure and excess internal
pressure for the above liquid systems at 298·15K using two different approaches. In the conventional approach one needs the
experimental values ofα andβ
T of mixtures for computing internal pressure, which was not possible. The second method which is proposed here utilizes only
the density, ultrasonic velocity and viscosity data of the mixture. This method is used in computing internal pressure and
its excess value for multicomponent liquid systems. A satisfactory agreement has been observed. 相似文献
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E. Comay 《Foundations of Physics Letters》1989,2(4):383-388
A recent article, claiming to identify an electromagnetic system with a field whose group velocity is faster than light, is disproved. 相似文献