multi-Gaussian Schell-model Research Articles

Correlation singularities of partially coherent beams with multi-Gaussian correlation function

Correlation singularities of partially coherent beams with multi-Gaussian correlation function (i.e., multi-Gaussian Schell-model beams) are studied. It is shown that there exist correlation singularities for scalar multi-Gaussian Schell-model (MGSM) beams, both in the source plane and in the output plane. We find the simple relation between the correlation singularities and the beam index M of MGSM beams, i.e., the number of ring dislocations equals M−1, which may be used to determine the beam index M.

Propagation Properties of the Rectangular Multi-Gaussian Schell-Model Beams in Uniaxial Crystals Orthogonal to the Optical Axis

A stochastic beam generated by a recently introduced source of Schell type with rectangular multi-Gaussian spectral degree of coherence is shown to posses interesting novel features on propagation in uniaxial crystals. The analytical expression for the cross-spectral density function of the rectangular multi-Gaussian Schell-model (RMGSM) beams propagating in uniaxial crystals orthogonal to the optical axis is derived. With the help of the derived formula, the evolution properties of the spectral density, the effective beam width, and the spectral degree of coherence of the RMGSM beams in a uniaxial crystal are investigated in detail. It is shown that the evolution properties of an RMGSM beam in uniaxial crystal are much different from its evolution properties in free space, and the propagation properties of the RMGSM beams in uniaxial crystals are closely related to the initial beam parameters (beam index M and spatial coherence length) and the parameters of the uniaxial crystals (the ratio of extraordinary and ordinary refractive indices). The results demonstrate the potential of uniaxial crystals for modulating the properties of the RMGSM beams.

Polarization properties of Square Multi-Gaussian Schell-Model beam propagating through non-Kolmogorov turbulence

In this paper, analytical expressions for elements of the cross-spectral density matrix of Square Multi-Gaussian Schell-Model (SMGSM) beam, propagating in non-Kolmogorov turbulence, are derived based on the extended Huygens Fresnel integral. Polarization properties of the SMGSM beam are studied in detail based on the derived expressions. It is interesting to find that, apart from keeping the square flat shape of intensity distribution, polarization properties of the SMGSM beam, such as degree of polarization, the orientation angle and degree of ellipticity for the polarization ellipse also form square plateau distributions in the same areas as that of intensity distribution, and can preserve relatively long distance in atmospheric turbulence. This novel characteristic can be used for coherent light free space communications, polarization remote sensing and imaging in atmosphere.

Evolution properties of multi-Gaussian Schell model beams propagating in uniaxial crystal orthogonal to the optical axis

Evolution properties of multi-Gaussian Schell model beams propagating in uniaxial crystal orthogonal to the optical axis

Spreading and evolution behavior of coherent vortices of multi-Gaussian Schell-model vortex beams propagating through non-Kolmogorov turbulence

The explicit closed-form expressions for the beam width and angular spread of multi-Gaussian Schell-model vortex (MGSMV) beams propagating through atmospheric turbulence are derived in this paper. The spreading and evolution behavior of coherent vortices of MGSMV beams in non-Kolmogorov turbulence are investigated quantitatively by some typical numerical examples, where the evolution behavior of coherent vortices is stressed in particular. It is illustrated that MGSMV beams are more resistant to atmospheric turbulence than multi-Gaussian Schell-model (MGSM) non-vortex beams. By increasing the beam index of MGSMV beams, the deleterious turbulence effects can be reduced gradually. As MGSMV beams propagate in non-Kolmogorov turbulence, the position and number of coherent vortices are changeable. The impact of the beam index and fluctuations of atmospheric turbulence on the conservation distance of the topological charge is also explored in depth.

The intensity properties of a Multi-Gaussian Schell-model pulse scattering from a sphere with semisoft boundaries

The scattering of a Multi-Gaussian Schell-model pulse from a sphere with semisoft boundaries within the accuracy of the first-order Born approximation is investigated. The analytic expression for the average intensity of the scattered pulse in the far zone is derived. The numerical calculations are performed in order to show the dependence of the average intensity of the scattered field on the incident pulse duration, the temporal coherence length of the incident pulse, the upper summation index and the effective radius of the medium. The effect of the boundary’s softness on the scattered intensity distribution is emphasized. It is shown that, comparing with that of scattering from a Gaussian sphere, the average intensity distribution of the pulse scattering from a sphere with semisoft boundaries has two or three peaks under certain circumstances.

Propagation properties of electromagnetic rectangular multi-Gaussian Schell-model beams in oceanic turbulence

A model of electromagnetic rectangular multi-Gaussian Schell-model (ERMGSM) beams is introduced. Its analytic expression for the elements of the cross-spectral density matrix of such beams passing through oceanic turbulence is derived. It is shown that the rectangular shape of the ERMGSM beams holds a small distance on propagation in oceanic turbulence. The spectral density, the degree of coherence and the degree of polarization of ERMGSM beams are also studied in detail. The results will be helpful for underwater communication by using ERMGSM beams.

Propagation properties of a Multi-Gaussian Schell-Model beam in a uniaxial crystal orthogonal to the optical axis

This article presents the investigation of the propagation properties of a Multi-Gaussian Schell-Model (MGSM) beam in a uniaxial crystal, orthogonal to the optical axis. The analytic expressions for the elements of the cross-spectral density matrix of an MGSM beam in such a crystal are derived. Using the derived expressions for numerical analysis, the distributions of the normalized intensity and degree of polarization for MGSM beams are studied. The results show that not only does the normalized distribution intensity of the beam form a flat shape, but also the distribution of degree of polarization reaches a plateau in the central area when propagating in a uniaxial crystals orthogonal to the optical axis. The parameters of the source and refractive indices are major factors that affect the distributions. With a suitable choice of parameters, the intensity distribution changes to a rounded rectangular plateau and the degree of polarization distribution changes to an elliptic plateau. The results also indicate that a uniaxial crystal can modulate these MGSM beam distributions, which is beneficial for the optical manipulation of microscopic particles and nonlinear optics, involving a specific profile and polarization.

Propagation of multi-Gaussian Schell-model beams in oceanic turbulence

Based on the extended Huygens–Fresnel principle, the general analytic expression for the cross-spectral density function of the multi-Gaussian Schell-model beams is derived and used to investigate the spectral densities of multi-Gaussian Schell model beams propagating through oceanic turbulence. With the help of this expression, numerical calculations are illustrated and the results show that the flat intensity profile is destroyed by choosing suitable parameters.

Propagation of multi-Gaussian Schell-model vortex beams in isotropic random media.

The effect of isotropic and homogeneous random media on propagation characteristics of recently introduced multi-Gaussian Schell-model (MGSM) vortex beams is investigated. The analytical formula for the cross-spectral density function of such a beam propagating in random turbulent media is derived and used to explore the evolution of the spectral density, the degree of coherence and the turbulence-induced spreading. An example illustrates the fact that, at sufficiently large distance from the source, the source correlations modulation of the spectral distribution in free space is shown to be suppressed by the uniformly correlated turbulence. The impacts, arising from the index M, the correlation width of the source and the properties of the medium on such characteristics are analyzed in depth.

Scintillation reduction in pseudo Multi-Gaussian Schell Model beams in the maritime environment

Irradiance fluctuations of a pseudo Multi-Gaussian Schell Model beam propagating in the maritime environment is explored as a function of spatial light modulator cycling rate and estimated atmospheric turnover rate. Analysis of the data demonstrates a strong negative correlation between the scintillation index of received optical intensity and cycling speed for the estimated atmospheric turnover rate.

Nonparaxial propagation of a multi-Gaussian Schell-model beam

Based on the vectorial Rayleigh–Sommerfeld diffraction integral formulas, analytical expressions for the elements of 3 × 3 cross-spectral density matrix of polarized multi-Gaussian Schell-model (MGSM) beam’s nonparaxial propagation in free space are derived, and used to investigate its propagation properties. As a special case of nonparaxial propagation, the paraxial case has also been considered by the reduced paraxial approximation expressions. The distributions of spectral density, spectral degree of coherence, and spectral degree of polarization of nonparaxial MGSM beam are illustrated by numerical examples. Results show that the statistical properties of MGSM beam’s nonparaxial propagation in free space are closely related to the initial beam’s correlation width related parameter and transverse width related parameter These characteristics of MGSM beam might find applications in laser scanning, optical trapping, and free space optical communication.

Nonparaxial propagation of a rectangular multi-Gaussian Schell-model beam

Abstract According to the vectorial Rayleigh–Sommerfeld diffraction integral formulas, analytical expressions for the elements of 3×3 cross-spectral density matrix of polarized Rectangular Multi-Gaussian Schell-Model (RMGSM) beam’s nonparaxial propagation in free space are derived, and the paraxial analytical expression has also been presented as a special case of nonparaxial propagation. Its statistical properties, including the distributions of spectral density, spectral degree of coherence, and spectral degree of polarization of nonparaxial RMGSM beam are numerically demonstrated. Results reveal that the statistical properties of RMGSM beam’s nonparaxial propagation in free space are closely related to the initial beam’s transverse width σ and correlation widths δ x and δ y . These characteristics of RMGSM beam might be useful in optical material surface processing, imaging, and free space optical communication.

Trapping two types of particles with a focused generalized Multi-Gaussian Schell model beam

We numerically investigate the trapping effect of the focused generalized Multi-Gaussian Schell model (GMGSM) beam of the first kind which produces dark hollow beam profile at the focal plane. By calculating the radiation forces on the Rayleigh dielectric sphere in the focused GMGSM beam, we show that such beam can trap low-refractive-index particles at the focus, and simultaneously capture high-index particles at different positions of the focal plane. The trapping range and stability depend on the values of the beam index N and the coherence width. Under the same conditions, the low limits of the radius of low-index and high-index particles for stable trapping are indicated to be different.

多高斯-谢尔模型光束在海洋湍流中的传输特性研究

多高斯-谢尔模型光束在海洋湍流中的传输特性研究

Effects of multi-Schell beams on orbital angular momentum of entangled signal photons in low-order turbulence aberration channels

We model the detection and crosstalk probability of orbital angular momentum (OAM) states of the entangled signal photon in the Kolmogorov channels of the low-order turbulence aberrations and by the Rytov approximation. The results show that lower OAM mode number of signal photons and larger sub-beam number of multi-Gaussian Schell-model pump beam, the less susceptible of the detection probability of the signal photon to spatial coherence of source and turbulence aberrations is achieved. The maximum crosstalk probability is decrease as the decreasing of the sub-beam number of multi-Gaussian Schell-model. Enlarging OAM difference value or decreasing sub-beam number of multi-Gaussian Schell-model pump beam results in a lower crosstalk probability of the OAM of entangled signal photons.

Random source generating far field with elliptical flat-topped beam profile

Circular and rectangular multi-Gaussian Schell-model (MGSM) sources which generate far fields with circular and rectangular flat-topped beam profiles were introduced just recently (Sahin and Korotkova 2012 Opt. Lett. 37 2970; Korotkova 2014 Opt. Lett. 39 64). In this paper, a random source named an elliptical MGSM source is introduced. An analytical expression for the propagation factor of an elliptical MGSM beam is derived. Furthermore, an analytical propagation formula for an elliptical MGSM beam passing through a stigmatic ABCD optical system is derived, and its propagation properties in free space are studied. It is interesting to find that an elliptical MGSM source generates a far field with an elliptical flat-topped beam profile, being qualitatively different from that of circular and rectangular MGSM sources. The ellipticity and the flatness of the elliptical flat-topped beam profile in the far field are determined by the initial coherence widths and the beam index, respectively.

Optical trapping Rayleigh particles by using focused multi-Gaussian Schell-model beams

We numerically investigate the radiation forces of multi-Gaussian Schell-model (MGSM) beams, in which the degree of coherence is modeled by the multi-Gaussian function, exerted on the Rayleigh dielectric sphere. By simulation of the forces calculation it is found that the steepness of the edge of the intensity profile (i.e., the summation index M) and the initial coherence width of the MGSM beams play important roles in the trapping range and stability. We can increase the trapping range at the focal plane by increasing the value of M or decreasing the initial coherence of the MGSM beams. It is also found that the trapping stability becomes lower due to the increase of the value of M or the decrease of coherence. Furthermore, the trapping stability under different conditions is explicitly analyzed. The results presented here are helpful for some possible applications.

The control of pulse profiles with tunable temporal coherence

Abstract A new class of partially coherent pulse sources with Multi-Gaussian Schell-model (MGSM) correlations is proposed. The expression for the intensity distribution for the MGSM pulses generated by such sources on propagation through the dispersive media is derived. It is demonstrated that the pulse intensity profile, in particular, the width of the flat center of pulse intensity profile and the peak intensity, can be controlled by adjusting the source temporal coherence. The obtained results have potential applications in pulse shaping for communication and media sensing or pulsed laser material processing.

Rectangular Multi-Gaussian Schell-Model beams in atmospheric turbulence

Optical beams radiated by a recently introduced class of Rectangular Multi-Gaussian Schell-Model (RMGSM) source are examined on propagation in free space and in atmospheric turbulence, with both classic and non-classic power spectra of the refractive-index fluctuations. The expression for the cross-spectral density function of such beams has been derived and used for the analysis of their spectral density (average intensity). The RMGSM beams are shown to preserve the square/rectangular shape of the transverse intensity distribution and the maximum intensity level in the flat part for relatively large distances from the source on propagation in classic turbulence. This makes the novel beams attractive for free-space optical communications and surface processing in the presence of the atmosphere.