WoS İndeksli Yayınlar Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/8653
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Article Citation - WoS: 41Citation - Scopus: 46Transmittance of Partially Coherent Cosh-Gaussian, Cos-Gaussian and Annular Beams in Turbulence(Elsevier Science Bv, 2007) Eyyuboglu, Halil T.; Baykal, YahyaAverage relative power transmittance is evaluated, by incorporating atmospheric turbulence, for partially coherent cosh-Gaussian, cos-Gaussian, Gaussian and annular beams. For all the collimated versions of these beams, against the increasing propagation length, there is a typical trend of the decrease in the relative average power transmittance with incremental drop being much less for partially coherent cos-Gaussian beams. The change in the transmittance versus the propagation length will be similar to the corresponding collimated cases, when these beams are focused at a certain focal length. Also partially coherent beams are less sensitive to propagation length changes, except for cos-Gaussian case. Partially coherent cosh-Gaussian beams exhibit a drop in the transmittance as the displacement parameter of the beam is made larger, whereas this trend is just the opposite for partially coherent cos-Gaussian beams. When examined versus the source size, for all the four types of beams, the transmittance has a similar behavior, i.e., it becomes high at small source sizes, falling with increasing source size, and following a dip, it starts to rise, eventually approaching the plane wave limit of unity. The occurrence of the dip coincides with the smallest source size for cosh-Gaussian, with the largest for cos-Gaussian, and about the same source size for Gaussian and annular beams. In general, the average relative power transmittance of coherent beam is affected much more than the partially coherent beams against the variations in source properties. (c) 2007 Elsevier B.V. All rights reserved.Article Citation - WoS: 20Citation - Scopus: 21Apertured Averaged Scintillation of Fully and Partially Coherent Gaussian, Annular Gaussian, Flat Toped and Dark Hollow Beams(Elsevier Science Bv, 2015) Eyyuboglu, Halil T.; Eyyuboʇlu, Halil T.Apertured averaged scintillation requires the evaluation of rather complicated irradiance covariance function. Here we develop a much simpler numerical method based on our earlier introduced semianalytic approach. Using this method, we calculate aperture averaged scintillation of fully and partially coherent Gaussian, annular Gaussian flat topped and dark hollow beams. For comparison, the principles of equal source beam power and normalizing the aperture averaged scintillation with respect to received power are applied. Our results indicate that for fully coherent beams, upon adjusting the aperture sizes to capture 10 and 20% of the equal source power, Gaussian beam needs the largest aperture opening, yielding the lowest aperture average scintillation, whilst the opposite occurs for annular Gaussian and dark hollow beams. When assessed on the basis of received power normalized aperture averaged scintillation, fixed propagation distance and aperture size, annular Gaussian and dark hollow beams seem to have the lowest scintillation. Just like the case of point-like scintillation, partially coherent beams will offer less aperture averaged scintillation in comparison to fully coherent beams. But this performance improvement relies on larger aperture openings. Upon normalizing the aperture averaged scintillation with respect to received power, fully coherent beams become more advantageous than partially coherent ones. (C) 2014 Elsevier B.V. All rights reserved.Article Citation - WoS: 4Citation - Scopus: 4Complex Degree of Coherence and Power Moments of Cylindrical Sinc Gaussian Beam(Elsevier Science Bv, 2015) Eyyuboglu, Halil T.; Eyyuboʇlu, Halil T.Complex degree of coherence and power moment aspects of cylindrical sinc Gaussian beam are investigated. To do this, we have used the random phase screen approach. It is seen that on the source plane, cylindrical sinc Gaussian beam has zero on-axis intensity and the sidelobes resemble the sinc or the Gaussian profile depending on the relative magnitudes of width parameter and the source size. Upon propagation in turbulent atmosphere, the initially flat complex degree of coherence becomes curved as the beam propagates, it then partially follows the intensity profile, and eventually turns into a delta function. Power moments are evaluated up to the fifth degree and over two different aperture sizes. In the aperture size of pointlike scintillations, the behaviors of power moments are similar to those of intensity moments. In aperture averaging conditions however, the differences between the variations of moments with respect to the propagation distance and degree of the moments become much less. (C) 2015 Elsevier B.V. All rights reserved.Article Citation - WoS: 11Citation - Scopus: 11Non-Kolmogorov Spectrum Scintillation Aspects of Dark Hollow and Flat Topped Beams(Elsevier Science Bv, 2012) Eyyuboglu, Halil T.; Cai, YangjianThe scintillation aspects of dark hollow (DH) and fiat topped (FT) beams propagating in the turbulent atmosphere containing the non-Kolmogorov power spectrum are investigated. It is found that low scintillations will occur when the exponent of the power spectrum is just above the numeric value of 3. Initially, the rises in scintillations will take place as the exponent becomes larger, but later the scintillation reductions will be experienced as the exponent grows further, eventually minimum scintillations will be seen when the exponent has reached the value of 4. This will be the case, for scintillation variations against propagation distance, source size, wavelength, inner and outer scales of turbulence. Furthermore, it is found that at the small source sizes, DH beams will offer less scintillation than FT beams, while at the large source sizes, the reverse will be applicable. (C) 2011 Elsevier B.V. All rights reserved.Article Citation - WoS: 18Citation - Scopus: 18Minimization of Scintillation Index Against Displacement Parameters(Elsevier Science Bv, 2008) Eyyuboglu, Halil T.; Gercekcioglu, Hamza; Baykal, YahyaFor sinusoidal beams, minimization of scintillation index is carried out against the displacements parameters. It is found-that x-y asymmetric cosh-Gaussian beam fulfills the requirements of such optimum beam. Our minimization procedure reveals that the optimum beam is achieved by continually focusing it at the chosen propagation length and by further adjusting displacements parameters to be propagation distance dependent. Scintillation index of thus constructed optimum beam is formulated and numerically evaluated., Our graphical comparisons entailing collimated and focused versions of cos-, cosh-Gaussian, annular-Gaussian and Gaussian beams show that the optimum beam yields the lowest scintillations provided that Propagation range is less than or equal to the focusing distance. (C) 2008 Elsevier B.V. All rights reserved.Article Citation - WoS: 54Citation - Scopus: 59Propagation Characteristics of Higher-Order Annular Gaussian Beams in Atmospheric Turbulence(Elsevier Science Bv, 2006) Eyyuboglu, Halil T.; Altay, Serap; Baykal, YahyaThe propagation characteristics of higher-order annular Gaussian (HOAG) beams in turbulence are investigated. From a HOAG source plane excitation, the average intensity of the receiver plane is developed analytically. This formulation is verified against the previously derived HOAG beam solution in free space. The graphical outputs indicate that, upon traveling in turbulent atmosphere, the HOAG beam will undergo different stages of evolution. At intermediate propagation distances, it will attempt to concentrate the energy near the origin. In this process, the appearance of the single higher-order primary beam will be encountered. Eventually HOAG originated beam will become a pure Gaussian beam after propagating an excessive distance in the turbulent medium. (c) 2006 Elsevier B.V. All rights reserved.Article Citation - WoS: 78Citation - Scopus: 83Convergence of General Beams Into Gaussian-Intensity Profiles After Propagation in Turbulent Atmosphere(Elsevier Science Bv, 2006) Baykal, Yahya; Sermutlu, Emre; Eyyuboglu, Halil T.It is shown that a general shaped laser beam will eventually approach a Gaussian average intensity profile after propagation in turbulent atmosphere. In our formulation, source field at the exit plane of the laser is taken as the product of arbitrary functions of source transverse coordinates with Gaussian exponential modulations. Following the expansion of the arbitrary functions in terms of Hermite polynomials, the average receiver intensity expression is derived using the extended Huygens-Fresnel principle and the conditions for the intensity profile to assume a Gaussian shape are stated. The results are illustrated by simulating various source field distributions. (c) 2006 Elsevier B.V. All rights reserved.Article Citation - WoS: 19Citation - Scopus: 19Off-Axis Beam Intensity in Random Medium(Elsevier Science Bv, 2007) Baykal, Yahya; Eyyuboglu, Halil T.The receiver intensity profile of an off-axis-Gaussian beam travelling in random medium is formulated. By examining the related exponential terms of this intensity expression, the rules governing the receiver plane displacements are deduced. Off-axis-Gaussian beam is characterized by introducing into a Gaussian beam, complex displacement parameters that exhibit transverse source coordinate dependent attenuation and phase shifts. Our results are applied to turbulent horizontal links. Intensity plots describing the dependence on the source and propagation parameters both on the source and the receiver planes are provided. Even though the normalized intensities of the off-axis-Gaussian beam having the same source sizes but differing displacements in x- and y-directions may look the same on the source plane, they will differentiate after propagation. The views from the progress of an off-axis-Gaussian beam along the turbulent link length show that a source displaced beam will act according to rules set by related exponential terms. An asymmetrical (ellipsoidal) off-axis-Gaussian beam will initially be converted into symmetric (circular) shape at the intermediate link lengths, then it will start to expand in the other direction, thus reverting to an ellipsoid shape whose major axis is now along the transverse coordinate opposite to that of the source plane. (c) 2006 Elsevier B.V. All rights reserved.