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利用小波变换(WT)对超短高斯脉冲光束作时频分析,获得了光脉冲的时间分辨功率谱,给出了在1个脉冲周期内频随时间变化的关系。对光脉冲在自由空间传输的时频谱特性进行了研究,结果表明:在离轴点上,时频谱相对光束中心出现明显的时间延迟,而频谱分布不变。 相似文献
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本文分析了单周期超短脉冲光束在色散介质中的传输特性,给出了相应的解析解。结果当脉冲宽度短至几个光学周期时,时空参量之间的耦全变得很重要,并将引起脉冲光束的非对称。 相似文献
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研究了部分相干超短脉冲光束的M2因子。从时空维格纳分布函数出发,以高斯-谢尔(GSM)脉冲光束为例,导出部分相干超短脉冲光束的M2因子公式。给出了空间完全相干高斯脉冲光束和准单色高斯-谢尔脉冲光束的M2因子。由于受脉冲光束带宽及空间相关度的影响,高斯-谢尔脉冲光束的M2因子总是大于1。研究结果表明,M2因子随脉冲光束带宽的增大而增大,随空间相关度的增大而减小。此外,对于啁啾高斯-谢尔脉冲光束,M2因子还随啁啾参数的增大而增大。 相似文献
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基于光束在单轴晶体中的傍轴矢量传输理论,对双曲正弦平方-高斯光束在单轴各向异性晶体中垂直于光轴的传输做了研究,得到了一般的解析传输公式,并用数值计算方法分析了该光束的传输特性。研究表明:由于晶体的各向异性,其原来的偏振特性将不再保持,仅沿x方向偏振的初始场分量衍生出y分量;随着传输距离的增加,非寻常光沿x轴和z轴的偏振场慢变振幅均减小,光强峰值也随之减小。此外,双曲正弦平方-高斯光束在单轴晶体中垂直于光轴传输时,光束参数β取值不同,光强呈现不同的分布状态。 相似文献
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应用Wigner分布函数的二阶矩定义和拓展Huygens–Fresnel原理研究了圆形平顶高斯光束阵列在湍流大气传输中的光束性质,得到其传输质量因子( 因子)的解析表达式,进行了相应的数值计算和模拟。结果表明:在湍流大气中传输时,圆形平顶高斯光束阵列的传输质量因子随传播距离、湍流大气结构常数的增大和束腰宽度的减小而增大;当光束阵列阶数一定,阵列个数不断增加时,其传输质量因子先保持不变,然后开始减小,最后不再减小,而保持这个定值不变;当光束阵列的个数一定,阶数不断增加时,其传输质量因子减小,最后不再减小而保持不变。在自由空间中传输时,圆形平顶高斯光束阵列的传输质量因子保持不变。 相似文献
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《Microwave Theory and Techniques》1970,18(8):455-460
For propagation in lossless waveguide, the rigorous impulse response function is given. It is shown that its instantaneous frequency is that which has reached the output at that time by propagating at the group velocity. For a square envelope pulse with a carrier frequency /spl omega/ above the cutoff frequency /spl omega//sub c/, the propagation of the envelope and of the phase are essentially described by the group and phase velocity, respectively. In addition, however, the bulk of the pulse is preceded by the so-called Sommerfeld precursors having an increasing amplitude and a frequency which decreases from a high value to /spl omega/. Similarly the bulk of the pulse k followed by the Sommerfeld postcursors in which both amplitude and frequency decrease, the latter from /spl omega/ to /spl omega//sub c/. The analytic results are illustrated by computed examples of waveguide transients. 相似文献
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G. M. Strelkov 《Journal of Communications Technology and Electronics》2008,53(9):1034-1043
Analytic solution of the problem on propagation of a frequency-modulated radio pulse in cold isotropic collisional plasma is presented. The solution does not involve the Fourier integral and is not restricted to the distance of propagation or to the a priori choice of the shape of the initial pulse envelope. Rectangle pulses with linear and V-shaped frequency modulation and a trapezoidal pulse with linear frequency modulation are considered. The obtained solution is applied to analysis of distortions of such pulses during propagation along an ionospheric path. It is shown that the solution is efficient in the analysis of the uncertainty function of a propagating pulse 相似文献
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The known result for the output reading of a quasi-peak detector to periodic pulse inputs is here extended to cover inputs made up of regularly repeated pulses of the same shape, but with random amplitudes. The cosine envelope was chosen for the pulse shape and is viewed as a satisfactory approximation for the typical IF amplifier impulse response. The probability distribution for the pulse amplitude was assumed uniform over an amplitude interval; the latter is a parameter in the analysis so that the result applies, at one extreme, to pulses ranging randomly from zero amplitude to some maximum, and at the other extreme, to fixed amplitude pulses. Solutions are provided for low-frequency inputs-such as would be developed at the output of an IF amplifier followed by an envelope detector, and RF inputs-such as would be found directly at the IF amplifier output. 相似文献
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The exact solution describing steady-state resonant pulse propagation in a two-level inverted medium is given. This steady-state pulse is often referred to as a 180° or π-pulse. No approximation of a slowly varying envelope is made, and hence the solution satisfies the second-order wave equation as well as the equations of motion of the density matrix of the system. As a result the theory is able to describe very short pulses, whose width can be of the order of the period of the optical carrier. The model for the system includes a nonresonant loss and a finite value of the transverse relaxation time T2 , but neglects dispersion in the host medium. The steady-state pulse is found to be frequency modulated and asymmetric in shape. 相似文献
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Yee J.H. Mayhall D.J. Sieger G.E. Alvarez R.A. 《Antennas and Propagation, IEEE Transactions on》1991,39(9):1421-1427
The state of research on intense electromagnetic pulse propagation in air and in waveguides is reviewed. Some results obtained from recent investigations of the propagation of intense electromagnetic pulses in the atmosphere and in an air-filled waveguide when the field strength is above the threshold for air breakdown are presented. It is shown how the air breakdown affects the shape of the pulse. In addition, the accuracy of the calculational models is discussed, comparing calculations with experimental data 相似文献
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An investigation of the propagation of electromagnetic pulses in a weakly nonlinear, cold, collisionless plasma is described. It is found that a transverse electromagnetic pulse generates, through nonlinear effects, a small amplitude, longitudinal electric pulse field. The transient behavior of this longitudinal electric field is studied. One particular case is considered in detail: the nonlinear generation of a longitudinal electric field by a transverse electromagnetic pulse which is excited by a suddenly turned-on cosinusoidal electric field of frequencyomega_{0} . Computer plots of numerical calculations of the second-order transient longitudinal field are presented. 相似文献
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通过数值求解非线性薛定谔方程,研究了三阶色散效应对基孤子脉冲在单模光纤中传输的影响.结果表明,在三阶色散作用下,基孤子脉冲在传输过程中被展宽,峰值能量逐渐减小,脉冲形状发生畸变,脉冲的中心偏向一侧,并形成非对称的拖尾振荡结构;当与二阶色散共同作用时,三阶色散引起的脉冲振荡会变缓.考虑非线性效应后,在一定程度上补偿了由于色散效应导致的峰值功率的减小,同时抑制了非对称拖尾结构的产生. 相似文献
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The propagation of lateral electromagnetic waves and pulses on microstrip is investigated. Interference patterns generated by the superposition of the lateral and direct waves along the air-substrate surface are shown. The field generated by the pulse excitation of a horizontal dipole on the air-substrate boundary is shown to consist of a lateral-wave pulse and a slower direct-wave pulse. Their differences in shape and decay rate are clarified. It is shown that the shape of a Gaussian pulse propagating along an open microstrip transmission line is closely related to the shape of the lateral electric-field pulse generated by a Gaussian current pulse in a dipole on the air-substrate boundary 相似文献