Liuzhan Pan

Phase singularities and spectral changes of spectrally partially coherent higher-order Bessel-Gauss pulsed beams

Phase singularities and spectral changes of spectrally partially coherent higher-order Bessel-Gauss pulsed beams in free-space propagation are studied, and the analytical expressions for the spectral degree of coherence and spectrum are derived. It is shown that there always exists an optical vortex at the center of the beam and the topological charge is conserved during the propagation. Some circular edge dislocations appear and the spectrum changes on propagation. A rapid spectral transition takes place. Numerical illustrative examples are given and the results are explained physically.

Scattering-induced changes in the degree of polarization of a stochastic electromagnetic plane-wave pulse

The scattering of a stochastic electromagnetic plane-wave pulse on a deterministic spherical medium is investigated. An analytical formula for the degree of polarization (DOP) of the scattered field in the far zone is derived. Letting pulse duration T(0) → ∞, our formula can be applied to study the scattering of a stationary stochastic electromagnetic light wave. Numerical results show that the DOP of the far zone field is closely determined by the size of the spherical medium when the incident field is a stochastic electromagnetic plane-wave pulse. This is much different from the case when the incident field is a stationary stochastic electromagnetic light wave, where the DOP of the far zone field is independent of the size of the medium. One may obtain the information of the spherical medium by measuring the scattering-induced changes in the DOP of a stochastic electromagnetic plane-wave pulse.

Effect of oceanic turbulence on the propagation of cosine-Gaussian-correlated Schell-model beams

On the basis of the extended Huygens–Fresnel principle, the analytic expression for the cross-spectral density function of the cosine-Gaussian-correlated Schell-model (CGSM) beams propagating in oceanic turbulence is derived and used to investigate the spectral density and spectral degree of coherence of CGSM beams. The dependence of the spectral density and spectral degree of coherence of CGSM beams on the oceanic turbulence parameters including temperature-salinity balance parameter ω, mean square temperature dissipation rate χT and energy dissipation rate per unit mass is stressed and illustrated numerically. It is shown that oceanic turbulence plays an important role in the evolution of spectral density and spectral degree of coherence of CGSM beams upon propagation.

Correlation singularities of a partially coherent radially polarized beam in non-Kolmogorov turbulence

We have investigated the correlation singularities of a partially coherent radially polarized beam propagating through non-Kolmogorov turbulence. An analytical expression for the radius of a ring dislocation is derived. It is shown that the dependence of the radius of a ring dislocation on spatial coherence width in non-Kolmogorov turbulence is quite different from that in free space. The relation between spatial coherence width and beam width affects the change trends of the radius of a ring dislocation versus spatial coherence width. For different value ranges of the power law, the change of the radius of a ring dislocation with power law has an opposite trend. It is also found that the propagation distance plays an important role in determining the change of the radius of a ring dislocation. Our results will be useful in measuring the statistical properties of a random medium or a random field.

Effect of dispersion on the spectrum of partially coherent beams

Taking the Gaussian Schell-model (GSM) beam as a typical example of partially coherent beams, the analytical expressions of the spectrum of GSM beams propagating in dispersive media are derived, and the spectral properties are studied in detail. It is shown that, in comparison with propagation in free space and in turbulence, whether or not GSM beams satisfy the scaling law, the normalized spectrum of GSM beams in dispersive media changes on propagation in general, because the dispersive medium affects different spectral components differently. As compared with the free-space propagation, for the scaling-law GSM beams the dispersion results in spectrum change, and for the nonscaling-law GSM beams the dispersion gives rise to a further increase in spectral changes. The structure constant of the dispersive property of the media, the transverse coordinate of the observation point, the spatial correlation length of the source, and the propagation distance affect the spectral behavior of GSM beams; this effect is illustrated numerically.

Propagation properties of stochastic electromagnetic non-uniformly correlated partially coherent pulses in dispersive media

The scalar model of non-uniformly correlated partially coherent pulses is extended to the full electromagnetic domain and the realizability conditions of stochastic electromagnetic non-uniformly correlated partially coherent (SENUC) pulse sources in the frequency domain are derived. It is shown that the evolution properties of the intensity and degree of polarization (DOP) of the SENUC pulse in dispersive media in the frequency domain are much different from those of an SENUC pulse in the temporal domain. And the distribution of the intensity and DOP of the pulse on propagation is dependent on its spectral coherence width, shift parameters of the spectral correlation maximum and second-order dispersion coefficient.