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Abstract A novel class of random media with designed correlation functions are introduced. When light waves are scattered by this kind of media, the spectral density distributions of the scattered field present concentric rings-like profiles. By adjusting different parameters of the media, the number and the size of concentric rings can be modulated properly. Besides, it is found that the spectral density function of the scattered field and the non-negative definiteness function of the media belong to the same kind of functions. Our results have potential applications in optical trapping and particle manipulation. [ABSTRACT FROM AUTHOR]

An annular beam has the ability to self-transform into a non-diffractive beam when it propagates in air at a long distance. In our previous study, we propagated an annular beam in random media and obtained a non-diffractive beam at a short propagation distance of a few tens centimeters by adjusting the concentration of random media and narrowing the view angle of the receiver. In this paper, we aim to analyze the components and characteristics of a non-diffractive beam and elucidate how the non-diffractive beam is generated in random media. The intensity variation of the scattered waveform is examined when the distance between the receiver and the back plane of a medium tank is changed. The waveform scattered in random media is constructed from forward scattering light at the center and multiple scattering light in the surrounding part. The forward scattering light at the center generates the non-diffractive beam. In numerical analysis based on diffusion theory, the calculation result of the non-diffractive beam shows agreement with the experimental result. [ABSTRACT FROM AUTHOR]

Beam propagation has been given important attention in a variety of applications in medicine, remote sensing and information science. Especially, the beam propagation in highly scattering media, which is called random media, is important. In general, the multiple scattering gets rid of beam characteristics, e.g., intensity distribution, phase front, and polarization. In this study, self-converging effect of annular beam was applied in random media. Diluted milk was used as random media, and the transmitted light was detected with a narrow view angle of 5.5mrad. The collimated annular beam of a few tens millimeters takes a few hundred meters to transform its beam shape into the non-diffractive beam in free space, while this transformation was shorten only to 20 cm in random media, that is, the collimated annular beam caused its transformation at only 20 cm in random media. The transformed beam kept its optical characteristics of “non-diffractive beam”. Such transformation of the annular beam needs the appropriate condition of random media. Media concentration and propagation distance control the generation of the center peak intensity of the transformed beam. This study indicates the generation of the non-diffractive beam in random media and reveals its appropriate condition. [ABSTRACT FROM AUTHOR]

A novel technique is given and implemented to generate correlated phase screens that are used in the study of laser propagation through turbulent atmosphere. The method can generate random fields with nonzero expected values and is applied to simulate equally and arbitrary spaced phase screens. In both cases, it proves to be very computationally efficient. [ABSTRACT FROM AUTHOR]

It takes a long distance of more than 200 m to generate a non-diffractive beam from an annular beam of 40 mm φ (diameter) in space. The authors have worked on the generation, control and optimization of a non-diffractive beam in random media with a short distance (a few tens of centimeters). In this work, the transmittance and the forward scattering waveforms of an annular beam at different propagation distances in random media are presented. Higher intensity of the center peak of a non-diffractive beam can be generated for short-distance propagation and high concentration in random media. The random media under consideration have the same scattering coefficients for all propagation distances. These scattering coefficients depend on the balance between forward scattering and multiple scattering. This balance is defined as the weight parameter α. By using the parameter α, an optimization of a non-diffractive beam in random media is proposed, which is based on adjusting the concentration and the propagation distance in random media. [ABSTRACT FROM AUTHOR]

Stochastic interference of fluorescence light outgoing from a dye-doped coarse-grained random medium, which was pumped by the continuous-wave laser radiation, was experimentally studied. It was found that the contrast of random interference patterns highly correlates with the wavelength-dependent fluorescence intensity and reaches its minimum in the vicinity of the cusp of emission spectrum. The decay in the contrast of spectrally selected speckle patterns was interpreted in terms of the pathlength distribution broadening for fluorescence radiation propagating in the medium. This broadening is presumably caused by the wavelength-dependent negative absorption of the medium. [ABSTRACT FROM AUTHOR]

Abstract: We study the coherence properties of the field generated by beam radiated from quasi-homogeneous (QH) electromagnetic source scattering on QH media. Formulas for the spectral density and spectral degree of coherence of the three dimensional scattered field are derived. The results show under assumption that the diagonal correlation coefficients of the source are proportional to each other, the far field of the scattered light satisfy two reciprocity relations analogous to that in the scalar case, that, the spectral density is proportional to the convolution of the spectral density of the source and the spatial Fourier transform of the correlation coefficient of the scattering potential; the spectral degree of coherence is proportional to the convolution of the diagonal correlation coefficients and the strength of the scattering potential. [Copyright &y& Elsevier]

Abstract: Deviations in the behavior of structural function of a heated turbulent medium refractive index are studied in laboratory and natural experiments. It is shown that these deviations should be connected with the heating and helicity level of this medium. [Copyright &y& Elsevier]

The intensity correlation properties of multiple scattered light reflected from various kinds of dense powders are investigated experimentally. The correlation coefficient of the resulting speckle patterns is measured by changing the angle and the area of laser beam illumination. The proportional relationship between the transport mean free path and the average particle diameter is obtained when the powder samples of the same kind are used in the angular correlation measurements. The transport mean free path also depends strongly on the adhesiveness of powder particles. The speckle correlation measurement for translation of the illuminating area on the powder surface shows that the particle size has almost no effect on the rate of speckle decorrelation. This result indicates that the translational correlation method is not suitable for particle size measurements. [Copyright &y& Elsevier]

The problem of polarized light propagating through scattering media can be explained using the vector radiative transfer equation. This equation is an integro-differential equation and is well-known to be unsolvable analytically. One of the approximate solutions is discrete ordinates method which is based on the discretization of the Stokes parameters and the Mueller matrix. Although it produces accurate results, it requires a lot of computational resources. In addition, there are limitations on the calculation for angles that are very close to the optical axis. The solutions at these angles are necessary for some applications such as atmospheric imaging. First-order scattering approximation has been applied to mitigate the computational resource situation. It can also be used to calculate the solution at the angles that are very close to optical axis. However, it lacks information about the cross-polarization and it is inaccurate when light encounters more scattering events. Second-order scattering approximation provides more accurate solutions and offers some information about cross-polarization. We develop the first-order and second-order scattering approximations and their solutions for the pulse wave case. We investigate the second-order approximation solutions and compare them to the solution from the complete vector radiative transfer equation in several cases. [Copyright &y& Elsevier]

The statistical properties of randomized electromagnetic field have been investigated by simulating the scattering of electromagnetic waves by random media (RMs). In the viewpoint of a theoretical requirement, the probability density function of perfectly randomized field satisfies the zero-mean circular Gaussian (ZMCG) statistics. We find that Kullback–Leibler Divergence (KLD) can quantitatively evaluate the randomness of an electromagnetic field to improve the design of RMs. There are two types of RMs which can efficiently randomize the electromagnetic waves only by monotonically increasing the permittivity of scatterers. When both the permittivity and total number of scatterers are fixed, KLD always have a limitation in any practical RM, which are characterized by a plateau on the evolutionary curve. • We present a better Kullback–Leibler Divergence method to measure randomness of a field. • A plateau showing in a KLD evolution is explained by the law of large numbers. • Kullback–Leibler Divergence shows that an unconfirmed but widely accepted assumption is invalid. [ABSTRACT FROM AUTHOR]