Scopus İndeksli Yayınlar Koleksiyonu

Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/8651

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Institution Author: search.filters.institutionAuthor.Baykal, YahyaSubject: search.filters.subject.Atmospheric Turbulence

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Now showing 1 - 9 of 9
  • Conference Object
    Citation - Scopus: 1
    Intensity Fluctuations of Incoherently Superposed Gaussian Beams in Atmospheric Turbulence
    (Spie-int Soc Optical Engineering, 2010) Baykal, Yahya
    Intensity fluctuations of incoherently superposed Gaussian beams are formulated in weak turbulence by employing the extended Huygens-Fresnel principle. Each individual beam superposed is taken to be fully incoherent. The scintillation index evaluated for different number of beams indicates that as the number of beams increase, scintillations decrease. Incoherent superposition of smaller sized Gaussian sources exhibits smaller fluctuations. Comparing the scintillation index arising from incoherently superposed Gaussian beams to the scintillation index of coherently superposed Gaussian beams of the same structure shows that incoherent superposition yields lower intensity fluctuations, thus can be advantageous in atmospheric optical communication links.
  • Conference Object
    Citation - WoS: 5
    Citation - Scopus: 10
    Beams With Arbitrary Field Profiles in Turbulence - Art. No. 652209
    (Spie-int Soc Optical Engineering, 2006) Baykal, Yahya
    Characteristics of optical beam incidences that have arbitrary field profiles are examined when they propagate in the turbulent atmosphere. Arbitrary source field profile is introduced by decomposing the source into incremental areas and the received field in the presence of turbulence is expressed as the summation of the fields originating from each incremental area. Intensity moments such as average intensity and the scintillation index in turbulence are formulated under such excitation. Our results correctly reduce to the well established Gaussian beam wave solutions when the arbitrary source beam is taken as the Gaussian field profile. Naturally, all the beam structures such as the higher-order single-mode, multimode, off-axis Hermite-Gaussian, Hermite-sinusoidal-Gaussian, higher-order annular, flat-topped-Gaussian beams form the special cases of our derivation. Numerical results that cover the scintillations in turbulence for various types of arbitrary beam profiles are presented. Our results for the arbitrary source field profiles can be applied in atmospheric optics telecommunication links where combination of several known beams are employed as incidence in an effort to reduce the degrading effects of turbulence. Also in the problems of reflection from rough surfaces, propagation of spatially partially coherent optical beams or double passage imaging in turbulence, our formulation can be utilized.
  • Conference Object
    Citation - WoS: 3
    Citation - Scopus: 4
    Intensity Fluctuations for Source Arrays in Turbulent Atmosphere - Art. No. 630308
    (Spie-int Soc Optical Engineering, 2006) Baykal, Yahya
    Intensity fluctuations are formulated for source arrays in weakly turbulent horizontal atmospheric links. Source array is composed of point sources separated by variable distances in the transverse source directions. Formula yielding the on-axis scintillation index for the source array is derived by employing the Rytov solution for the structure and correlation functions in the extended Huygens Fresnel principle. Through numerical results, variations of the scintillations versus the array parameters such as the size of the array, spacing between the array elements, amplitudes and phases of the individual sources in the array are investigated. Numerically evaluated intensity fluctuations for such array parameters are compared with the well known single point source scintillations. We are interested to understand whether the use of a source array will give favorable intensity fluctuations in atmospheric communication links.
  • Article
    Citation - WoS: 23
    Citation - Scopus: 23
    Ber of Asymmetrical Optical Beams in Oceanic and Marine Atmospheric Media
    (Elsevier Science Bv, 2017) Baykal, Yahya
    The average bit-error-rate (BER) performances of asymmetrical optical Gaussian beams propagating in oceanic and marine atmospheric turbulence are examined. Both type of media are assumed to exhibit weak turbulence. The effect of asymmetry factor on the BER performance are investigated in conjunction with the oceanic turbulence parameters of the ratio of temperature to salinity contributions to the refractive index spectrum, the rate of dissipation of mean-squared temperature and the rate of dissipation of kinetic energy per unit mass of fluid, and with the marine atmospheric link parameters of the link length and the structure constant. Also, the variations of the BER against the source size of various asymmetrical beams are scrutinized in both oceanic and marine atmospheric media.
  • Article
    Citation - WoS: 22
    Citation - Scopus: 21
    Multimode Laser Beam Scintillations in Non-Kolmogorov Turbulence
    (Ieee-inst Electrical Electronics Engineers inc, 2015) Baykal, Yahya
    Employing the Rytov solution, the scintillation index at the origin of the receiver plane is evaluated in non-Kolmogorov weak atmospheric turbulence when multimode laser incidence is used. The solution presented can be used when the multimode is composed of even modes. The novelty of this work lies in the theoretical combination of multimode laser beam excitation and non-Kolmogorov turbulence in the scintillation evaluations, which is not known both theoretically and experimentally. The study involves mathematical rigor but no experimental results. Being valid for any power law exponent of the non-Kolmogorov turbulence, the scintillations of the multimode beams are found to be smaller than the scintillation index of a single Gaussian beam. For the multimode laser beam excitation, the scintillation index is smaller at smaller power law exponent values. If the multimode content is formed by beams with larger mode numbers, the scintillations decrease for any non-Kolmogorov realization. When large sized beams are used in the multimode, the scintillations increase as compared to small sized content, and the scintillations become almost the same as the Gaussian beam scintillations. Comparing the multimode structures that have the same number of beams, the ones with higher order modes yield smaller scintillations, and for such multimode structures, very similar scintillation index behaviour versus the power law exponent can be obtained by varying the amplitudes of the modes composing the multimode. The main contribution of this paper is the formulation and evaluation of the scintillation noise in order to understand whether the use of multimode laser excitation will improve the link performance of optical wireless communication systems operating in a non-Kolmogorov atmosphere.
  • Article
    Citation - WoS: 8
    Citation - Scopus: 8
    Crossbeam Intensity Fluctuations in Turbulence
    (Spie-soc Photo-optical instrumentation Engineers, 2014) Baykal, Yahya
    Intensity fluctuations of a crossbeam are evaluated in weak atmospheric turbulence. A crossbeam is defined as two asymmetrical Gaussian beams oriented perpendicular to each other, and one of these beams is wider along the x-axis whereas the other beam is wider along the y-axis. Our results indicate that in terms of the intensity fluctuations in weak turbulence, focused crossbeams offer favorable results when compared to the corresponding focused Gaussian beam intensity fluctuations. However, for collimated crossbeams, such a comparison is in favor of the collimated Gaussian beam. (C) 2014 Society of Photo-Optical Instrumentation Engineers (SPIE)
  • Article
    Citation - WoS: 6
    Citation - Scopus: 6
    Field Correlations for Off-Axis Gaussian Laser Beams in Atmospheric Turbulence
    (Amer Geophysical Union, 2014) Baykal, Yahya
    The absolute field correlations in atmospheric turbulence are evaluated for the off-axis optical Gaussian beam incidence. Evaluations in the practical range of the source and the turbulent medium parameters show that an increase in the diagonal length at the receiver plane causes the absolute field correlations of the off-axis Gaussian beam to decrease. At a fixed receiver diagonal length, the off-axis Gaussian beams having smaller displacement parameters and larger source sizes exhibit larger absolute field correlations. Comparing the absolute field correlations of the off-axis Gaussian beams in atmospheric turbulence with their no turbulence counterparts, it is observed that the behavior of the absolute field correlation variations remains the same; however, the diminishing of the absolute field correlations in turbulence occurs at smaller diagonal lengths.
  • Article
    Citation - WoS: 16
    Citation - Scopus: 17
    Sinusoidal Gaussian Beam Field Correlations
    (Iop Publishing Ltd, 2012) Baykal, Yahya
    Field correlations of sinusoidal Gaussian beams are formulated in turbulence, and specifically cos Gaussian (cG) and cosh Gaussian (chG) beam field correlations are evaluated versus the diagonal length at the receiver plane. The effects of the displacement parameters, the coordinates of the first receiver point and the source sizes on the field correlations of monochromatic light sources having cG and chG field distributions are investigated when such beams traverse turbulent media. Such parameters affect spatial heterodyne measurement. Field correlations found at the receiver plane reflect the combined variations of diffraction patterns and turbulence effects. To differentiate the diffraction patterns and the turbulence effects, field correlations of cG and chG beams in turbulence and in the absence of turbulence are compared. For cG beams, the oscillatory behaviour of the field correlations versus the diagonal length at the receiver plane in the absence of turbulence becomes smoother in the presence of turbulence. The received fields of cG and chG beams become decorrelated at shorter diagonal distances in turbulence.
  • Article
    Citation - WoS: 18
    Citation - Scopus: 19
    Field Correlations of Flat-Topped Gaussian and Annular Beams in Turbulence
    (Elsevier Sci Ltd, 2011) Baykal, Yahya
    Starting from the second order moment formulation for multi-beam incidence, field correlations at the receiver plane of flat-topped Gaussian and annular beams are found in turbulence. Reflecting the information on both the randomness due to turbulence and the field profile of the incident field, field correlations of the fiat-topped Gaussian beams are found to become larger at larger source size, smaller flatness parameters and smaller turbulence strengths. For the annular beam structures, field correlations are larger for thicker beams. Field correlations of larger primary beam sized annular incidences are smaller at smaller diagonal distances and larger at larger diagonal distances. As expected, annular beam field correlations are found to be larger at smaller structure constants and at smaller wavelengths. However, at large link lengths, field correlations could be larger than at smaller link lengths due to fact that for annular beams, the field at the centre of the receiver attains very small value at smaller link lengths, however, on propagation in turbulence, receiver field distribution changes to a Gaussian profile. (C) 2011 Elsevier Ltd. All rights reserved.