Elektronik ve Haberleşme Mühendisliği Bölümü Yayın Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/260
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Conference Object Propagation of Partially Coherent Beams After a Source Plane Ring Aperture(Electromagnetics Acad, 2008) Eyyuboğlu, Halil Tanyer; Eyyuboglu, H. T.; Baykal, Yahya Kemal; Baykal, Y. K.; Cai, Y.; Elektronik ve Haberleşme Mühendisliği; Elektrik-Elektronik MühendisliğiThe propagation properties of partially coherent beams passing through a source placed ring aperture are examined. The derivation is based on the lowest order general beam formulation, such that our results are applicable to a wide range of beam. In this study, our focus is on fundamental Gaussian, cosh-Gaussian, cos-Gaussian, sinh-Gaussian, sine-Gaussian and annular beams. The aperture consists of inner and outer parts, thus the middle hollow part appears in the form of a ring. The propagation environment is turbulent. From the graphical outputs of the beams investigated, it is seen that despite the existence of the circular ring, during propagation, the beams tend to retain the basic profiles similar to the case of no aperture, but depending on the inner and outer radius dimensions, the propagated beams are reduced in intensity levels and become more spread. It is further observed that, when the inner part of the aperture has nonzero radius, ring formations are developed at the outer edges of the receiver plane intensities.Conference Object Citation - WoS: 1Formulation of Scintillations for Optical Incidence of Arbitrary Field Profile(Electromagnetics Acad, 2008) Eyyuboğlu, Halil Tanyer; Baykal, Y.; Eyyuboglu, H. T.; Baykal, Yahya Kemal; Cai, Y.; Elektronik ve Haberleşme Mühendisliği; Elektrik-Elektronik MühendisliğiScintillation index on the receiver axis is formulated in random medium when an optical source with an arbitrary field profile is employed. To represent the arbitrary source field profile, source is decomposed into pixels and the incident field to form the scintillations is expressed as the superposition of the fields from each pixel area. Thus obtained arbitrary field distribution is then introduced into the weak atmospheric turbulence formulation by using Rytov method. Our result, which is in summa ion and integral forms, reduces correctly to the known scintillation index of a Gaussian beam wave in atmospheric turbulence.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: 31Citation - Scopus: 36Beam Wander of Dark Hollow, Flat-Topped and Annular Beams(Springer Heidelberg, 2008) Cil, C. Z.; Eyyuboglu, H. T.Benefiting from the earlier derivations for the Gaussian beam, we formulate beam wander for dark hollow (DH) and flat-topped (FT) beams, also covering the annular Gaussian (AG) beam as a special case. Via graphical illustrations, beam wander variations of these beams are analyzed and compared among themselves and to the fundamental Gaussian beam against changes in propagation length, amplitude factor, source size, wavelength of operation, inner and outer scales of turbulence. These comparisons show that in relation to the fundamental Gaussian beam, DH and FT beams will exhibit less beam wander, particularly at small primary beam source sizes, lower amplitude factors of the secondary beam and higher beam orders. Furthermore, DH and FT beams will continue to preserve this advantageous position all throughout the considered range of wavelengths, inner and outer scales of turbulence. FT beams, in particular, are observed to have the smallest beam wander values among all, up to certain source sizes.Article Citation - WoS: 57Citation - Scopus: 64Intensity Fluctuations in J-Bessel Beams of All Orders Propagating in Turbulent Atmosphere(Springer, 2008) Sermutlu, E.; Baykal, Y.; Cai, Y.; Korotkova, O.; Eyyuboglu, H. T.The scintillation index of a J (n) -Bessel-Gaussian beam of any order propagating in turbulent atmosphere is derived and numerically evaluated at transverse cross-sections with the aid of a specially designed triple integral routine. The graphical outputs indicate that, just like the previously investigated J (0)-Bessel-Gaussian beam, higher-order members of the family also offer favorable scintillation characteristics at large source sizes. This advantage is maintained against rising beam orders. Viewed along the propagation axis, beams with lower orders and smaller widths exhibit smaller values of the scintillation index at shorter propagation distances and large values at longer propagation distances. Further, it is shown that the scintillation index of the J (n) -Bessel-Gaussian beams (n > 0) is larger than that of the fundamental Gaussian and the J (0)-Bessel-Gaussian beams only near the on-axis points, while remaining smaller towards the edges of the beam.Article Citation - WoS: 13Citation - Scopus: 17Correlation Properties of Random Electromagnetic Beams in Laser Resonators(Springer Heidelberg, 2009) Tong, Z.; Korotkova, O.; Cai, Y.; Eyyuboglu, H. T.; Baykal, Y.With the help of the generalized Huygens-Fresnel principle and the tensor approach for electromagnetic stochastic beams we investigate the behavior of their two-point spatial correlation properties on interaction with a laser resonator. In particular, the evolution of the degree of coherence, of the degree of cross-polarization and of the intensity correlations (at one and two points in space) is analyzed for typical beams and cavities. The theory is illustrated by numerical curves pertaining to various correlation properties of typical electromagnetic Gaussian Schell-model beams.Article Citation - WoS: 10Citation - Scopus: 12Concept of Area Scintillation(Springer, 2009) Eyyuboglu, H. T.Stemming from the results of our earlier investigations, the concept of area scintillation is introduced, which takes into account the intensity distribution over the receiver plane. In this context, the area scintillation of fundamental Gaussian and annular beams is formulated, numerically evaluated and graphically illustrated. From the comparison, it is seen that, under the same source power conditions, annular Gaussian beams provide much less scintillations than the fundamental Gaussian beams at small source size. At large source sizes and at shorter propagation distances, annular beams are still favorable, but, as the propagation range is extended, the reverse becomes true. A review of previous findings leading up to the newly introduced concept is also presented.Article Citation - WoS: 26Citation - Scopus: 26Beam Wander Characteristics of Cos and Cosh-Gaussian Beams(Springer, 2009) Eyyuboglu, H. T.; Cai, Y.; Baykal, Y.; Cil, C. Z.Within the context of a general beam formulation, beam wander characteristics of cos and cosh-Gaussian beams are derived and numerically evaluated. In our graphs, the fundamental Gaussian beam is used as a benchmark for comparisons. The associated plots reveal that at small source sizes, a cos-Gaussian beam has the lowest beam wander, while this property is enhanced with increasing values of the displacement parameter. At large source sizes however, this advantage is taken over by cosh-Gaussian beam. Joint examination against the changing source sizes and propagation lengths shows that the range of source sizes, where the beam wander of cos-Gaussian beam remains lower, is enlarged as we go toward higher propagation lengths. Asymmetric beams tend to exhibit higher beam wanders both at small and large source sizes, but for the intermediate source size ranges, the beam wanders of asymmetric beams will fall below those of the symmetric beams. Explanations concerning these behaviors are offered. A historical account of beam wander formulation is also included.Article Citation - WoS: 13Citation - Scopus: 13Comparison of Wave Structure Functions for Intensity Profiles(Springer, 2009) Eyyuboglu, H. T.We give a list of available wave structure functions (WSFs) of a spherical wave, simultaneously providing some derivation details. The aim is to assess the impact of these WSFs on intensity profiles of various beams propagating in turbulence. For comparisons, coherent and partially coherent fundamental Gaussian, hyperbolic, sinusoidal and annular Gaussian beams are chosen. Comparisons are made by calculating the difference between the intensity profiles of the analytic solution that uses the normalized WSF with quadratic approximation and the intensity profiles obtained by numerically solving the quadruple extended Huygens-Fresnel integral containing other WSFs. The graphical results show that in general the differences arising from the use of different WSFs are not substantial. Such differences become much greater however toward the complete incoherence limit and at relatively higher structure constant values. Even then, at these extremes, the receiver intensity levels are much reduced, making such big differences immaterial.Article Citation - WoS: 12Citation - Scopus: 13Generalized Tensor Abcd Law for an Elliptical Gaussian Beam Passing Through an Astigmatic Optical System in Turbulent Atmosphere(Springer, 2009) Cai, Yangjian; Lin, Q.; Eyyuboglu, H. T.; Baykal, Y.The propagation of an elliptical Gaussian beam (EGB) through an astigmatic ABCD optical system in a turbulent atmosphere is investigated. An analytical formula for the average intensity of an EGB and a generalized tensor ABCD law for the generalized complex curvature tensor are derived. As an application example, we derived an analytical formula for the average intensity of an elliptical flat-topped beam propagating through an astigmatic ABCD optical system in a turbulent atmosphere. As a numerical example, the focusing properties of an EGB focused by a thin lens in a turbulent atmosphere are studied. It is found that the focused beam at the focal plane becomes a circular Gaussian beam when the atmospheric turbulence is strong enough, and the beam width of the circular Gaussian beam is determined by atmospheric turbulence strength, focal length of the thin lens, and wavelength of the initial beam but is independent of the initial beam widths (i.e., initial intensity distribution).