Electromagnetic Pulsed Beams Research Articles

Far-zone behaviors of scattering-induced statistical properties of partially polarized spatially and spectrally partially coherent electromagnetic pulsed beam**Project supported by the National Natural Science Foundation of China (Grant No. 11504286), the Natural Science Basic Research Program of Shaanxi Province, China (Grant No. 2019JM-470), the Fund from the International Technology Collaborative Center for Advanced Optical Manufacturing and Optoelectronic Measurement, and the Science

In this study, we explore the far-zero behaviors of a scattered partially polarized spatially and spectrally partially coherent electromagnetic pulsed beam irradiating on a deterministic medium. The analytical formula for the cross-spectral density matrix elements of this beam in the spherical coordinate system is derived. Within the framework of the first-order Born approximation, the effects of the scattering angle θ, the source parameters (i.e., the pulse duration T0 and the temporal coherence length Tcxx), and the scatterer parameter (i.e., the effective width of the medium σR) on the spectral density, the spectral shift, the spectral degree of polarization, and the degree of spectral coherence of the scattered source in the far-zero field are studied numerically and comparatively. Our work improves the scattering theory of stochastic electromagnetic beams and it may be useful for the applications involving the interaction between incident light waves and scattering media.

Characterizing the polarization and cross-polarization of electromagnetic vortex pulses in the space-time and space-frequency domain.

The dynamics of the degree of polarization and the degree of cross-polarization for electromagnetic pulsed vortex beams in dispersive media are explored both in the space-time and space-frequency domains. It is shown that the impacts, arising from the second-order dispersion coefficient and the temporal coherence length, on the variations of the temporal degree of polarization are distinctly different from those on the spectral degree of polarization. Besides, we also suggest a method to access the measurement of the orbital angular momentum of pulsed vortex beams through the mapping relationship between the distribution of the temporal degree of cross-polarization and the number of topological charge.

Effect of dispersion order on the spectral degree of polarization of stochastic electromagnetic pulsed beams

The analytical expression for the cross-spectral density function of stochastic electromagnetic Bessel–Gauss pulsed beams through a dispersive aperture lens is derived and used to study the changes in the spectral degree of polarization in an optical focus system. The changes in the spectral degree of polarization at the focal plane and on the z-axis are performed in the case of dispersion-free, dispersion of the first, second, and higher orders, respectively. It is shown that the dispersion affects the peak value of the spectral degree of polarization, and the higher order dispersion leads to a more obvious effect on the peak value of the spectral degree of polarization at the focal plane. On the z-axis, the spectral degree of polarization in the dispersion-free case is different form that in the dispersion case, however, the dispersion of different orders almost has the same effect on the spectral degree of polarization. The results obtained in this paper may be crucial for high precision laser detection.

Transverse electric and transverse magnetic pulsed-beam decomposition of time-dependent aperture fields

The present contribution is concerned with applying beam-type expansion to a planar aperture time-dependent (TD) electromagnetic field in which the propagating elements, the electromagnetic pulsed-beams, are a priori decomposed into transverse electric (TE) and transverse magnetic (TM) field polarizations. The propagating field is described as a discrete superposition of tilted, shifted, and delayed TE and TM electromagnetic pulsed-beam propagators over the frame spectral lattice. These waveobjects are evaluated by using TD plane-wave spectral representations. Explicit asymptotic expressions for electromagnetic isodiffracting pulsed-quadratic beam propagators are presented, as well as a numerical example.

Effect of Higher Order Axial Electron Temperature on Self-Focusing of Electromagnetic Pulsed Beam in Collisional Plasma

Effect of higher order axial electron temperature on self-focusing of electromagnetic pulsed beam in collisional plasma is investigated. It is shown that higher order axial electron temperature Tp4 is not trivial than Tp0 and Tp2, which can modify slightly radial redistribution of electron density and increases effective dielectric constant. As a result, on one hand, slightly reduce electromagnetic beam self-focusing in the course of oscillatory convergence, on the other hand, quicken beam divergence in the course of steady divergence, i.e., higher order axial electron temperature Tp4 can decrease the influence of collisional nonlinearity in collisional plasma.

Nonparaxial propagation of spatially and spectrally partially coherent electromagnetic Cosh-Gaussian pulsed beams

Based on the generalized Rayleigh–Sommerfeld diffraction integral, the analytical expression for 3×3 cross-spectral density matrix of nonparaxial spatially and spectrally partially coherent electromagnetic Cosh-Gaussian (ChG) pulsed beams propagating in free space is derived, and used to formulate the spectral density and spectral degree of polarization of electromagnetic pulsed beams at the z-plane. It is found that the parameters f and fαα are the key parameters in determining the nonparaxiality of spatially and spectrally partially coherent electromagnetic ChG pulsed beams. And the decentered parameter, pulse duration and temporal coherence length can change the nonparaxial behavior of the electromagnetic ChG pulsed beams. The effect of decentered parameter, pulse duration and temporal coherence length on the spectral density and spectral degree of polarization of electromagnetic ChG pulsed beams is illustrated through numerical calculations. Propagation of nonparaxial spatially and spectrally partially coherent electromagnetic Gaussian Schell-model pulsed beams can be treated as a special case when the decentered parameter of electromagnetic ChG pulsed beams approaches to zero.

部分相干方形平顶电磁脉冲光束经相位调制透镜的聚焦特性

部分相干方形平顶电磁脉冲光束经相位调制透镜的聚焦特性

Changes in the spectral degree of polarization of nonparaxial stochastic electromagnetic pulsed beams

By using the generalized vectorial Rayleigh-Sommerfeld diffraction integral, the analytical expression for the spectral degree of polarization (SDP) of stochastic spatially and spectrally partially coherent electromagnetic pulsed beams (SSSPCEPB) is derived, and used to study the changes in the SDP of SSSPCEPB in the nonparaxial regime. Similar to that of continuous beams, the f parameter and f αα parameter of pulsed beams also play an important role in determining the nonparaxiality of SSSPCEPB. However, the pulse duration and temporal coherence length of the pulse can change the nonparaxiality of SSSPCEPB. The dependence of SDP on the f parameter, pulse duration and temporal coherence length is emphasized and illustrated numerically.

Propagation of the degree of cross-polarization of stochastic electromagnetic pulsed beams in free space

The concept of the degree of cross-polarization is extended from stochastic electromagnetic stationary beams to stochastic electromagnetic pulsed beams, and the propagation properties of the degree of cross-polarization of stochastic spatially and spectrally partially coherent electromagnetic pulsed beams is studied. The influence of pulse duration and temporal coherence length on the degree of cross-polarization P is emphasized. It is shown that P exhibits an oscillatory behavior in free-space propagation. An increase in the pulse duration or a decrease in the temporal coherence length can weaken the oscillation of P. The validity of the results is interpreted physically.

Influence of Turbulent Atmosphere on Polarization Properties of Stochastic Electromagnetic Pulsed Beams

Using the coherence theory of non-stationary fields and the characterization of stochastic electromagnetic pulsed beams, the analytical expression for the spectral degree of polarization of stochastic electromagnetic Gaussian Schell-model pulsed (GSMP) beams in turbulent atmosphere is derived and is used to study the polarization properties of stochastic electromagnetic GSMP beams propagating through turbulent atmosphere. The results of numerical calculation are given to illustrate the dependence of spectral degree of polarization on the pulse frequency, refraction index structure constant and spatial correlation length. It is shown that, compared with free-space case, in turbulent atmosphere propagation there are two positions at which the on-axis spectral degree of polarization P is equal to zero. The position change depends on the pulse frequency, refraction index structure constant and spatial correlation length.

部分空间相干部分光谱相干厄米高斯脉冲电磁光束的偏振特性

部分空间相干部分光谱相干厄米高斯脉冲电磁光束的偏振特性

部分空间相干部分光谱相干双曲余弦高斯脉冲电磁光束在自由空间的传输特性

部分空间相干部分光谱相干双曲余弦高斯脉冲电磁光束在自由空间的传输特性

部分空间相干部分光谱相干厄米高斯脉冲电磁光束的偏振特性

部分空间相干部分光谱相干厄米高斯脉冲电磁光束的偏振特性

部分空间相干部分光谱相干厄米高斯脉冲电磁光束的偏振特性

部分空间相干部分光谱相干厄米高斯脉冲电磁光束的偏振特性

Influence of Polarization on the Spectral Changes of Stochastic Electromagnetic Pulsed Beams

An analytical expression for the spectrum of stochastic spatially and temporally partially coherent electromagnetic Gaussian Schell-model pulsed (GSMP) beams is derived, and used to study the spectral changes of electromagnetic GSMP beams in free space. The influence of polarization on the on-axis relative spectral shift is emphasized. It is shown that the on-axis relative spectral shift increases with increasing the degree of polarization of source P0 for the case of δxx≠δyy, i.e. the spatial coherence length δxx of x component of the electric field at the source is not equal to that of y component. For δxx=δyy or δxx→∞ and δyy→∞, the on-axis relative spectral shift is independent of P0.

Generalized Stokes parameters of stochastic spatially and spectrally partially coherent electromagnetic pulsed beams

The analytical expressions for the generalized (two-point) Stokes parameters of stochastic electromagnetic Gaussian Schell-model pulsed (GSMP) beams propagating in free space are obtained. The changes in the spectral Stokes parameters in free space propagation are studied. The dependence of on-axis and transverse spectral Stokes parameters of stochastic electromagnetic GSMP beams on the pulse parameters including pulse duration and temporal coherence length is stressed and illustrated numerically. The results are interpreted physically.

Changes in the spectrum, polarization, and coherence of stochastic spatially and spectrally partially coherent electromagnetic J0-correlated Schell-model pulsed beams propagating in free space

Taking the stochastic electromagnetic J 0 -correlated Schell-model pulsed (JSMP) beam as a typical example of stochastic spatially and spectrally partially coherent electromagnetic pulsed beams, the analytical expressions for the cross-spectral density matrix, spectral density, spectral degree of polarization and spectral degree of coherence of stochastic electromagnetic JSMP beams propagating in free space are derived, and used to study the changes in the spectrum, polarization, and coherence of stochastic spatially and spectrally partially coherent electromagnetic JSMP beams. It is shown that the on-axis spectrum is blue-shifted in free-space propagation and is dependent on the pulse temporal coherence length and spatial correlation parameter. The distribution of the on-axis spectral degree of polarization depends on the frequency and spatial correlation parameter. The spectral degree of coherence increases with increasing pulse temporal coherence length. The results derived are interpreted physically.

Characterization of stochastic spatially and spectrally partially coherent electromagnetic pulsed beams

The unified theory of coherence and polarization proposed by Wolf is extended from stochastic stationary electromagnetic beams to stochastic spatially and spectrally partially coherent electromagnetic pulsed beams. Taking the stochastic electromagnetic Gaussian Schell-model pulsed (GSMP) beam as a typical example of stochastic spatially and spectrally partially coherent electromagnetic pulsed beams, the expressions for the spectral density, spectral degree of polarization and spectral degree of coherence of stochastic electromagnetic GSMP beams propagating in free space are derived. Some special cases are analyzed. The illustrative examples are given and the results are interpreted physically.

Self‐focusing of an electromagnetic pulse in the ionosphere

In this paper, the self‐focusing of electromagnetic pulsed beams having Gaussian and sine profiles in the ionosphere have been studied. The self‐focusing of an electromagnetic pulse is caused by the nonlinearity in the dielectric function caused by the nonuniform distribution of electron temperature, determined by the Ohmic heating, solar radiation and energy loss in collisions with ions and neutrals. The radial distribution of the electron temperature causes a radial distribution of electron density and thereby that of the refractive index, which causes self‐focusing. The wave frequency has been assumed to be much larger than the electron collision frequency, and the temperature of the ions has been assumed to be equal to the temperature of neutrals; this assumption is justified in the ionosphere up to a height of 400 km. In the analysis, the electromagnetic wave equation and the energy balance equation has been solved simultaneously to obtain ordinary differential equations governing the beam width parameter and the electron temperature (on and away from the axis), respectively, in the paraxial approximation. For computations, the database for the midlatitude daytime ionosphere at the height of 150 km, compiled by Gurevich (1978), has been used. The transient behavior of the electron temperature (on and away from the axis) has been graphically presented for different values of pulse widths. The dependence of the beam width parameter on the distance of propagation for different times of retardation has also been plotted and discussed.

Self-focusing of electromagnetic pulsed beams in collisional plasmas

In this paper, the self-focusing of an electromagnetic pulsed beam in a collisional plasma has been investigated in the paraxial approximation, following the formalism developed by Akhmanov. The energy balance equation for electrons, the equation expressing the equality of pressure gradient (of electrons and ions) to the force due to space charge field, and the equation for the beam width parameter f (obtained by following Akhmanov’s approach) have been simultaneously solved for given initial (z=0) time profile of the pulse to obtain f as a function of ξ (cz∕ωr02) and t′=t−z∕Vg, where Vg is the group velocity. Both Gaussian and sine time profiles of the pulse have been investigated.