WoS İndeksli Yayınlar Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/8653
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Article Citation - WoS: 27Citation - Scopus: 28Beam Wander of J 0- and I 0-Bessel Gaussian Beams Propagating in Turbulent Atmosphere(Springer, 2010) Eyyuboglu, H. T.; Baykal, Y.; Korotkova, O.; Cai, Y.; Cil, C. Z.Root mean square (rms) beam wander of J (0)-Bessel Gaussian and I (0)-Bessel Gaussian beams, normalized by the rms beam wander of the fundamental Gaussian beam, is evaluated in atmospheric turbulence. Our formulation is based on the first and the second statistical moments obtained from the Rytov series. It is found that after propagating in atmospheric turbulence, the collimated J (0)-Bessel Gaussian and the I (0)-Bessel Gaussian beams have smaller rms beam wander than that of the Gaussian beam, regardless of the choice of Bessel width parameter. However, the extent of such an advantage depends on the chosen width parameter, Gaussian source size, propagation distance and the wavelength. Focusing at finite distances of the considered beams causes the rms beam wander to decrease sharply at the propagation distances equal to the focusing parameter.Article Citation - WoS: 60Citation - Scopus: 65Degree of Polarization for Partially Coherent General Beams in Turbulent Atmosphere(Springer, 2007) Eyyuboglu, H. T.; Baykal, Y.; Cai, Y.The degree of polarization is found for optical excitations of cosh-Gaussian, cos-Gaussian and annular-Gaussian beams in a turbulent atmosphere. The related formulation is based on the beam coherence polarization matrix. The self and mutual coherence functions appearing in the beam coherence polarization matrix are evaluated, when the above mentioned excitations exhibit partial source coherence for self and cross fields. Plots showing the variation of the degree of polarization are provided versus the propagation length when the source size, displacement parameter, structure constant and the degree of source coherence for self and cross fields change.Article Citation - WoS: 20Citation - Scopus: 21Scintillation Behavior of Laguerre Gaussian Beams in Strong Turbulence(Springer, 2011) Eyyuboglu, H. T.; Baykal, Y.; Falits, A.In strong atmospheric turbulence, the asymptotic on-axis scintillation behaviors of Laguerre Gaussian (LG) beams are examined. To arrive at the strong-turbulence solution, we utilize the existing filtering approach for weak-turbulence solutions and our recently reported weak-turbulence scintillation index formula for LG beams. In the limiting case, our solution correctly predicts the asymptotic strong-turbulence behavior of Gaussian beam wave scintillation. Investigation of the scintillations versus the propagation distance, source size, wavelength and refractive index structure parameter lead to the conclusion that the LG beams with higher order radial modes can provide less scintillation. The results are applicable to long-haul atmospheric optical communication links.Article Citation - WoS: 29Citation - Scopus: 32Intensity Fluctuations of Partially Coherent Laser Beam Arrays in Weak Atmospheric Turbulence(Springer, 2011) Arpali, C.; Arpali, S. A.; Baykal, Y.; Eyyuboglu, H. T.The intensity fluctuation of a partially coherent laser beam array is examined. For this purpose, the on-axis scintillation index at the receiver plane is analytically formulated via the extended Huygens-Fresnel diffraction integral in conditions of weak atmospheric turbulence. The effects of the propagation length, number of beamlets, radial distance, source size, wavelength of operation and coherence level on the scintillation index are investigated for a horizontal propagation path. It is found that, regardless of the number of beamlets, the scintillation index always rises with an increasing propagation length. If laser beam arrays become less coherent, the scintillation index begins to fall with growing source sizes. Given the same level of partial coherence, slightly less scintillations will occur when the radial distance of the beamlets from the origin is increased. At partial coherence levels, lower scintillations are observed for larger numbers of beamlets. Both for fully and partially coherent laser beam arrays, scintillations will drop on increasing wavelengths.Article Citation - WoS: 18Citation - Scopus: 22Partially Coherent Lorentz Gaussian Beam and Its Scintillations(Springer, 2011) Eyyuboglu, H. T.We study the scintillation aspects of partially coherent Lorentz Gaussian (LG) beams via numerically integrating the average and average squared intensity expressions. Within the examined range of input and propagation medium parameters, the LG beams are generally found to offer less and less scintillations against the pure Gaussian beam, particularly when the Lorentzian feature of the beam is emphasized more. This lower scintillation property is exhibited for collimated coherent beams with different Lorentz widths and at on-axis and off-axis positions of the receiver plane. When focusing is introduced, at shorter propagation distances the ordering of the beams remains as described above, but at longer propagations distances a complete reversing of the beam order is observed. Raising the turbulence levels by increasing the structure constant inevitably causes rises in scintillations, while preserving the advantage of LG beams over the pure Gaussian beam. Partial coherence reduces scintillations as expected, at the same time nearly eliminating the scintillation differences between the beam types.Article Citation - WoS: 13Citation - Scopus: 18Partially Coherent Elegant Hermite-Gaussian Beam in Turbulent Atmosphere(Springer, 2011) Cai, Y.; Eyyuboglu, H. T.; Baykal, Y.; Wang, F.Based on the extended Huygens-Fresnel integral, analytical formulas for the cross-spectral density, mean-squared beam width and angular spread of a partially coherent elegant Hermite-Gaussian (HG) beam in turbulent atmosphere are derived. The evolution properties of the average intensity, spreading and directionality of a partially coherent elegant HG beam in turbulent atmosphere are studied numerically. It is found that the partially coherent elegant HG beam with smaller initial coherence width, larger beam order and longer wavelength is less affected by the atmospheric turbulence. Compared to the partially coherent standard HG beam, the partially coherent elegant HG beam is less affected by turbulence under the same condition. Furthermore, it is found that there exist equivalent partially coherent standard and elegant HG beams, equivalent fully coherent standard and elegant HG beams, and an equivalent Gaussian-Schell-model beam may have the same directionality as a fully coherent Gaussian beam whether in free space or in turbulent atmosphere. Our results can be utilized in short and long atmospheric optical communication systems.Conference Object Citation - WoS: 7Citation - Scopus: 7Calculation of Average Intensity Via Semi-Analytic Method(Springer, 2010) Sermutlu, E.; Eyyuboglu, H. T.We present a semi-analytic approach to the solution of the quadruple Huygens-Fresnel integral which is used to calculate the average receiver intensity of a source beam after it has propagated in a turbulent atmosphere. Our approach is based on a self-designed MATLAB function that reduces a quadruple integral to a single one by sequential operations using a form that is readily available from tables. In this manner exact numerical evaluations are obtained, whilst lengthy hand derivations are avoided. Additionally, the computation time of the new approach is not much different from that of the complete analytic solution. Two application examples are cited, also establishing agreement with our previously published results.Article Citation - WoS: 23Citation - Scopus: 24Radius of Curvature Variations for Annular, Dark Hollow and Flat Topped Beams in Turbulence(Springer, 2010) Eyyuboglu, H. T.; Baykal, Y. K.; Ji, X. L.For propagation in turbulent atmosphere, the radius of curvature variations for annular, dark hollow and flat topped beams are examined under a single formulation. Our results show that for collimated beams, when examined against propagation length, the dark hollow, flat topped and annular Gaussian beams behave nearly the same as the Gaussian beam, but have larger radius of curvature values. Increased partial coherence and turbulence levels tend to lower the radius of curvature. Bigger source sizes on the other hand give rise to larger radius of curvature. Dark hollow and flat topped beams have reduced radius of curvature at longer wavelengths, whereas the annular Gaussian beam seems to be unaffected by wavelength changes; the radius of curvature of the Gaussian beam meanwhile rises with increasing wavelength.Article Citation - WoS: 21Citation - Scopus: 22Scintillation Calculations for Partially Coherent General Beams Via Extended Huygens-Fresnel Integral and Self-Designed Matlab Function(Springer, 2010) Eyyuboglu, H. T.; Baykal, Y.; Cai, Y.We present scintillation calculations in weak atmospheric turbulence for partially coherent general beams based on the extended Huygens-Fresnel integral and a Matlab function designed to handle expressions both of the average intensity and the average squared intensity. This way, the integrations are performed in a semi-analytic manner by the associated Matlab function, and this avoids lengthy, time-consuming and error prone hand derivations. The results are obtained for the partially coherent fundamental and higher-order sinusoidal and annular Gaussian beams. By plotting the scintillation index against the propagation distance and source size, we illustrate the on-axis scintillation behaviors of these beams. Accordingly, it is found that within specific source and parameter ranges, partially coherent fundamental, higher-order sinusoidal and annular Gaussian beams are capable of offering less scintillations, in comparison to the fundamental Gaussian beam.Article Citation - WoS: 20Scintillations of Partially Coherent Laguerre Gaussian Beams(Springer, 2010) Yuceer, M.; Eyyuboglu, H. T.; Lukin, I. P.Scintillations of Laguerre-Gaussian (LG) beams for weak atmospheric turbulence conditions are derived for on-axis receiver positions by using Huygens-Fresnel (HF) method in semi-analytic fashion. Numerical evaluations indicate that at the fully coherent limit, higher values of radial mode numbers will give rise to more scintillations, at medium and low partial coherence levels, particularly at longer propagation distances, scintillations will fall against rises in radial mode numbers. At small source sizes, the scintillations of LG beams having full coherence will initially rise, reaching saturation at large source sizes. For LG beams with low partial coherence levels, a steady fall toward the larger source sizes is observed. Partially coherent beams of medium levels generally exhibit a rising trend toward the large source sizes, also changing the respective positions of the related curves. Beams of low coherence levels will be less affected by the variations in the refractive index structure constant.