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 共查询到20条相似文献,搜索用时 31 毫秒
1.
刘涛  黄高明  王雪松  肖顺平 《物理学报》2009,58(5):3140-3153
Weibull分布的雷达极化回波特征由三个分布参数来描述:波的强度、极化椭圆率角以及椭圆倾角.在瞬态极化理论的基础上,推导了三个分布参数的联合概率密度函数,标准Stokes矢量统计分布的联合概率密度函数及其边缘概率密度函数,并通过蒙塔卡罗方法进行了计算机仿真,结果验证了理论推导的正确性.Weibull分布随机极化电磁波瞬态极化统计特性的研究对高分辨条件下雷达目标的检测、识别和跟踪领域都有一定的理论指导意义. 关键词: Weibull分布 极化椭圆参数 标准Stokes矢量 统计  相似文献   

2.
Salem M  Korotkova O  Wolf E 《Optics letters》2006,31(20):3025-3027
It is shown that two stochastic electromagnetic beams that propagate from the source plane z = 0 into the half-space z > 0 may have different degrees of polarization throughout the half-space, even though they have the same sets of Stokes parameters in the source plane. This fact is due to a possible difference in the coherence properties of the field in that plane, but other reasons are also possible. The result is illustrated by an example.  相似文献   

3.
Malus’ law, Fresnel-Arago interference laws and Stokes parameters are analyzed in the framework of the tensor theory of the electromagnetic spatial coherence wavelets. It is shown that these laws are suitable for each individual wavelet after regarding the correlation properties of the random electromagnetic field. Stokes parameters at the wavelet scale are introduced. They deal to generalized Stokes parameters which, in contrast to the classical ones, take into account the correlation properties of the random electromagnetic field on the aperture plane, that is the contributions of radiator pairs in surroundings of that plane.  相似文献   

4.
The role of temporal fluctuations and systematic variations of interaural parameters in localization of sound sources in spatially distributed, nonstationary noise conditions was investigated. For this, Bayesian estimation was applied to interaural parameters calculated with physiologically plausible time and frequency resolution. Probability density functions (PDFs) of the interaural level differences (ILDs) and phase differences (IPDs) were estimated by measuring histograms for a directional sound source perturbed by several types of interfering noise at signal-to-noise ratios (SNRs) between -5 and +30 dB. A moment analysis of the PDFs reveals that the expected values shift and the standard deviations increase considerably with decreasing SNR, and that the PDFs have non-Gaussian shape at medium SNRs. A d' analysis of the PDFs indicates that elevation discrimination is possible even at low SNRs in the median plane by integrating information across frequency. Absolute sound localization was simulated by a Bayesian maximum a posteriori (MAP) procedure. The simulation is based on frequency integration of broadly tuned "detectors." Confusion patterns of real and estimated sound source directions are similar to those of human listeners. The results indicate that robust processing strategies are needed to exploit interaural parameters successfully in noise conditions due to their strong temporal fluctuations.  相似文献   

5.
Analytic expressions and computed examples are given to elucidate the coherence and polarization properties of Stokes beams, i.e. beams formed by superposition of a completely unpolarized and a completely polarized electromagnetic Gaussian Schell-model beam. We found that superposition of such two beams cannot form a Stokes beam with a constant state of polarization on propagation. An additional constraint on the source plane parameters of the two Gaussian Schell-model beams is proposed. The resultant Stokes beam with a constant state of polarization on propagation is found to be a Gaussian Schell-model beam with the same variances as the two constituent Gaussian Schell-model beams. However, the modulus of the Gaussian intensity distributions across the source planes of these beams may be different.  相似文献   

6.
A simple characterization of the polarization state of partially polarized beams is proposed on the basis of the Stokes parameters expressed in terms of the radial and azimuthal components of the field at each point of the beam cross-section. The main properties of the proposed Stokes representation are also shown, and its physical meaning is discussed.  相似文献   

7.
Two overall parameters are proposed to characterize the degree of polarization and its uniformity across the transversal section of non-uniformly partially polarized beams. Such parameters can be measured according to the well-known standard methods used to obtain the Stokes parameters, with the addition of a CCD camera to determine the beam intensity at each point of the observation plane.  相似文献   

8.
舒建华  陈子阳  蒲继雄  刘永欣 《中国物理 B》2011,20(11):114202-114202
Based on vectorial Debye theory, the focusing properties of partially polarized vortex beam by high numerical aperture Fresnel zone plate are investigated. The effects of the numerical apertures of and the phase difference of binary phase Fresnel zone plates, the topological charge of vortex beam and the degree of polarization of incident beam on the intensity distribution and degree of coherence in the focal plane are investigated in detail. It is shown that elliptical light spots and the flat top beam can be obtained by selecting certain parameters. Studies of degree of coherence reveal that the degree of coherence between x and y components of the electric field, which is zero in the source plane, is improved in the focal plane for vortex beam, but it is hardly changed for the nonvortex beam. It is also proved that any two of the three electric field components Ex, Ey and Ez are completely coherent everywhere in the focal region if the incident light beam is linearly polarized.  相似文献   

9.
Setälä T  Tervo J  Friberg AT 《Optics letters》2006,31(14):2208-2210
We derive a spectral interference law that governs the behavior of the four Stokes parameters in Young's two-pinhole experiment with a random electromagnetic beam. In addition to the visibility of intensity fringes, we introduce three new contrast parameters that describe the interference-induced changes in the field's state of partial polarization. The polarization modulation depends on the electric field correlations at the pinholes and is closely related to the two-point Stokes parameters. The results are expected to be particularly useful in polarization interferometry and electromagnetic coherence theory. The formalism is demonstrated with specific examples.  相似文献   

10.
Owing to the recent observation of the strong anisotropy of characteristic X-ray radiation accompanying the resonant coherent excitation of relativistic Fe24+ ions under planar channeling conditions in a silicon crystal, the resonant coherent excitation method can be considered as a candidate for a source of polarized X-ray radiation. The Stokes parameters of the radiation have been calculated using the density matrix approach. The behavior of the polarization characteristics of the radiation in various directions has been explained by considering the properties of the resonance part of the crystal field, which excites an ion and has the form of an elliptically polarized electric field.  相似文献   

11.
Wang H  Wang X  Zeng A  Yang K 《Optics letters》2007,32(15):2215-2217
An analytical formula for the cross-spectral density matrix of the electric field of anisotropic electromagnetic Gaussian-Schell model beams propagating in free space is derived by using a tensor method. The effects of coherence on those beams are studied. It is shown that two anisotropic stochastic electromagnetic beams that propagate from the source plane z=0 into the half-space z>0 may have different beam shapes (i.e., spectral density) and states of polarization in the half-space, even though they have the same beam shape and states of polarization in the source plane. This fact is due to a difference in the coherence properties of the field in the source plane.  相似文献   

12.
Expressions for the Stokes parameters when radio waves propagate in a turbulent magnetoactive plasma have been obtained using a refractive scattering method. The problem of the spatial coherence of polarized radiation is considered. Expressions for the correlation functions and fluctuation dispersions of the Stokes parameters are found in the case of saturated wave field fluctuation. It is shown that the fluctuation of the circular polarized component will be observed in the received radiation even if the circular polarization is absent in the radiation that is incident on the magnetoactive plasma slab. A method is proposed to define the preference orientation of the magnetic field in the inhomogeneous layer of space plasma, which is biased on the simultaneous measurement of the space correlation functions of the I, V Stokes parameter fluctuation and Faraday rotation of the radiation polarization plane from the source with known polarization characteristics.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 39, No. 8, pp. 1007–1013, August, 1996.This work was supported in part by the Russian Foundation for Fundamental Research under Project No. 96-02-18632.  相似文献   

13.
Yuan GH  Wei SB  Yuan XC 《Optics letters》2011,36(17):3479-3481
Generation of a nondiffracting transversally polarized beam by means of transmitting an azimuthally polarized beam through a multibelt spiral phase hologram and then highly focusing by a high-NA lens is presented. A relatively long depth of focus (~4.84λ) of the electric field with only radial and azimuthal components is achieved. The polarization of the wavefront near the focal plane is analyzed in detail by calculating the Stokes polarization parameters. It is found that the polarization is spatially varying and entirely transversally polarized, and the polarization singularity disappears at the beam center, which makes the central bright channel possible.  相似文献   

14.
The statistics of polarization in electromagnetic waves or target vector has been studied deeply, generally using Stokes parameters. Unfortunately, all the data-processing includes the assumption that the sampling data are independent of time, without a consideration of the time coherence of the polarization data, such as instantaneous Stokes parameters. In this paper, the definitions of the instantaneous coherent polarization function and polarimetric spectrum are presented for the first time, which shows the coherences of the instantaneous Stokes parameters in both time and frequency domain, even in spatial coherence. The new formula of definition can be extended to spatial propagation coherence, both in free space or any linear medium.  相似文献   

15.
In a quasi-2D ferrite disk with a dominating role of magnetic–dipolar (non-exchange-interaction) spectra, one can observe the vortex structures. The vortices are guaranteed by the chiral edge states of magnetic–dipolar modes which result in appearance of eigen electric moments oriented normally to the disk plane. Due to the eigen-electric-moment properties, a ferrite disk placed in a microwave cavity is strongly affected by the cavity RF electric field with a clear evidence for multi-resonance oscillations. For different cavity parameters, one may observe the resonance absorption and resonance repulsion behaviors.  相似文献   

16.
Based on the extended Huygens–Fresnel principle, we study the propagation properties of partially coherent double-vortex beams in turbulent atmosphere. The intensity distribution of the beams on propagation and the influence of the characteristic parameters are investigated in great detail. It is shown that when the beams propagate in turbulent atmosphere, the intensity distributions are of double-ring structure near the source plane, but they will experience change, which are determined by the topological charges, the spatial coherence, source beam width and atmospheric turbulence. These results may have applications in space optical communication.  相似文献   

17.
Korotkova O  Wolf E 《Optics letters》2005,30(2):198-200
A generalization of the Stokes parameters of a random electromagnetic beam is introduced. Unlike the usual Stokes parameters, which depend on one spatial variable, the generalized Stokes parameters, depend on two spatial variables. They obey precise laws of propagation, both in free space and in any linear medium, whether deterministic or random. With the help of the generalized Stokes parameters, the changes in the ordinary Stokes parameters upon propagation can be determined. Numerical examples of such changes are presented. The generalized Stokes parameters contain information not only about the polarization properties of the beam but also about its coherence properties. We illustrate this fact by expressing the degree of coherence of the electromagnetic beam in terms of one of the generalized Stokes parameters.  相似文献   

18.
舒建华  陈子阳  蒲继雄 《光子学报》2014,40(11):1744-1750
基于德拜矢量积分理论,研究了随机电磁涡旋光束经过大数值孔径透镜之后的聚焦特性及透镜的数值孔径、入射光束的偏振度、拓扑荷以及横向相干长度对焦平面附近聚焦光束的光强分布和相干度的影响.结果表明:适当地选择相关参量,可在焦平面上得到椭圆形光斑的光强分布以及平顶光强分布.随机电磁涡旋光束在焦平面上同一点处两个相互垂直分量之间的相干度,不同两点处两个相同分量之间的相干度以及不同两点处两个相互垂直分量之间的相干度研究表明,入射光束的拓扑荷和横向相干长度对聚焦光束的相干性有着十分明显的影响.  相似文献   

19.
We consider the application of polarized radiation to the study of the properties of blood and erythrocyte suspensions, including the case of disturbance of the osmotic balance in the erythrocyte-surrounding-medium system. We study experimentally erythrocyte suspensions prepared by diluting whole donor blood with autoplasma, serum, and NaCl aqueous solutions of different concentrations. The Stokes parameters of scattered radiation have been measured with a Stokes polarimeter using a He-Ne laser as a source of linearly or elliptically polarized radiation (λ = 0.63 μm). We show that, upon illumination of erythrocyte suspensions with linearly or circularly polarized radiation, the Stokes parameters of the scattered radiation are highly sensitive to changes in the shape and size of erythrocytes upon hypotonic swelling.  相似文献   

20.
The properties of partially coherent Airy beam propagating in turbulent media are investigated. Firstly the variations in the intensity profile and the location of the Airy beam peak with respect to dislocation and width parameters are examined. On the source plane, it is shown that there is a threshold value of the dislocation parameter which determines whether the beam peak will lie on the negative or positive side of the axis. The changes in source beam power and source beam size with respect to dislocation and width parameters are also examined. Then analysis is made for partially coherent Airy beam propagating in turbulence against variations in propagation distance, dislocation and width parameters, structure constant and partial coherence. It is found that the peak of the Airy beam will always shift to the right for increasing propagation distance. But this shift will become less as the dislocation and width parameters are increased. Finally it is shown that higher levels of turbulence and partial coherence will lead to more spreading and shift the beam peak more toward the on-axis position.  相似文献   

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