Scopus İndeksli Yayınlar Koleksiyonu

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

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Author: search.filters.author.Baykal, YahyaDepartment: search.filters.department.Çankaya University

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Now showing 1 - 10 of 208
  • Article
    Citation - WoS: 1
    Scintillation Index in Non-Kolmogorov Jet Engine Exhaust Turbulence
    (IOP Publishing Ltd, 2026) Baykal, Yahya
    In a non-Kolmogorov jet engine exhaust turbulence environment, scintillation index is found and evaluated. Effects of non-Kolmogorov turbulence spectrum, i.e., power law on the scintillations are studied. Variations of the scintillations against the change in the power law are found for various link lengths, structure constants, wave numbers, jet engine exhaust turbulence strengths, source sizes and scale parameters of jet engine exhaust turbulence. When the power law of non-Kolmogorov turbulence varies, the changes in the scintillations in jet engine exhaust turbulence are not large. The results in this paper could be of help to designers of optical wireless communication systems operating in atmosphere experiencing non-Kolmogorov jet engine exhaust turbulence.
  • Article
    Transmittance of Gaussian Beam in Anisotropic Jet Engine Exhaust Turbulence
    (Pergamon-Elsevier Science Ltd, 2026) Baykal, Yahya
    Transmittance is a metric that provides information on how much of the intensity is transferred to the receiver for a given medium. One of the definitions of transmittance is the ratio of the average received intensity in the presence of turbulence to the received intensity in the absence of turbulence. Under such definition, transmittance is found in an anisotropic jet engine exhaust turbulent environment. For various receiver points, transmittances versus the wireless optical communication (WOC) link and anisotropic jet engine exhaust turbulence parameters are presented. The results are useful for designers of WOC links that are installed in the premises such as the airports that possess jet engine exhaust turbulence.
  • Article
    Mitigation of Laser Beam Fluctuation and Performance of Probability of Fade in Weak Ocean Turbulence
    (Pergamon-Elsevier Science Ltd, 2026) Gercekcioglu, Hamza; Baykal, Yahya
    Utilizing the Rytov method in weakly turbulent oceanic medium, minimum scintillation index of sinusoidal Gaussian (SG) laser beams, named as the optimum beam (OB), is investigated for the underwater wireless optical communication (UWOC). Horizontal link between any underwater vehicles is considered. The formulation of the on-axis scintillation index of these beams is derived analytically, and the minimum scintillation index is determined with suitable adjustment of the complex displacement parameters. The complex displacement parameters are identified and tabulated for the selected propagation distance and source size. Obtained scintillation index results are drawn against the propagation length and source size. When compared with the plane, spherical, collimated, focused Gaussian, cos-Gaussian and cosh-Gaussian beams, OB is found to possess essential advantage. Additionally, with the obtained scintillation index values, probabilities of fade of these beams are calculated and their behaviors are also presented. OB also has a significant advantage when considering the fade probability.
  • Article
    Laser Ablation Device with a Closed-Loop Control System
    (Optica Publishing Group, 2025) Beldek, Ulas; Erdogan, Kubra; Arpali, Caglar; Baykal, Yahya
    A laser ablation device with real-time beam power control is designed and implemented. This platform regulates the intensity of the laser beam by continuously measuring its intensity distribution. The quality of the ablation process is optimized through a closed-loop control system that uses a rule-based decision-making approach. The controller generates a starting signal for both the laser power and the motors based on the estimated quality of the ablation. The effects of laser power and light intensity on the formation of microchannels in polymethylmethacrylate material were investigated using the laser beam. The quality of the ablation geometry was assessed through image processing and inspection under a scanning electron microscope. The generated microchannels were analyzed in terms of roughness and residual thermal stress. A comparison of the experimental results with theoretical calculations and simulations revealed that the closed-loop control of laser beam power is effective for material etching and for creating smoother channel profiles. (c) 2025 Optica Publishing Group. All rights, including for text and data mining (TDM), Artificial Intelligence (AI) training, and similar technologies, are reserved.
  • Article
    Scintillation Characteristics of Annular Beam Array in Underwater Optical Links
    (IOP Publishing Ltd, 2025) Erdogdu, Ekin; Gokce, Muhsin Caner; Baykal, Yahya
    Underwater optical wireless communication systems offer a promising alternative to traditional acoustic methods for achieving high data rate transmission. However, the propagation of optical waves in underwater environments is severely impacted by oceanic turbulence, leading to intensity fluctuations and consequent performance degradation. In this work, we employ a laser beam array to model transmit spatial diversity for suppressing these fluctuations. The model uses annular-shaped lasers at the transmitter as a representation of beam shaping for turbulence mitigation, with a point detector assumed at the receiver. Through the use of the Huygens-Fresnel principle, we derive two key optical parameters: the average received intensity and the average of the intensity squared. We subsequently determine the scintillation index for this model. Our findings demonstrate reductions in scintillation under varying system parameters. For instance, increasing the number of beams in the array, the ring radius, and the secondary field amplitude of the annular beam leads to a lower scintillation index.
  • Conference Object
    Citation - WoS: 2
    Flat-Topped Field Correlations in Extremely Strong Turbulence
    (Electromagnetics Acad, 2011) Baykal, Yahya Kemal; Baykal, Yahya; Elektrik-Elektronik Mühendisliği
    In extremely strong turbulent horizontal atmospheric optical links, field correlations of flat-topped Gaussian incidence are evaluated. Field correlations are represented versus the diagonal distance at the receiver plane, for variations in the number of beams forming the flat-topped structure, receiver points, source sizes, link lengths, structure constants and the wave-lengths. Our results in extremely strong turbulence are compared to their free space counterparts which only reflect the diffraction patterns at the receiver plane. The effects of the inner scale of turbulence on the field correlations in extremely strong turbulence are examined in detail and it is observed that the size of the inner scale in extremely strong turbulence can considerably influence the field correlations of flat-topped beams.
  • Conference Object
    Citation - WoS: 1
    Citation - Scopus: 1
    Off-Axis Field Correlations in Turbulence
    (Ieee, 2013) Baykal, Yahya Kemal; Baykal, Yahya; Elektrik-Elektronik Mühendisliği
    The field correlations in atmospheric turbulence are evaluated for off-axis optical incidence. Within the practical range of the source and the medium parameters, increase in the diagonal length at the receiver plane is found to decrease the off-axis field correlations in turbulence. At a fixed diagonal length at the receiver plane, off-axis beams that have smaller displacement parameters and larger source sizes possess larger field correlations. When the field correlations of the off-axis beams in atmospheric turbulence are compared to their no turbulence counterparts, it is observed that the behaviour of the field correlation variations do not change, however the field correlations in turbulence diminish at smaller diagonal lengths.
  • Conference Object
    Aperture Averaging of Focused Multi-Gaussian Beams
    (Electromagnetics Acad, 2013) Baykal, Yahya Kemal; Kamacioglu, Callan; Baykal, Yahya; Yazgan, Erdem; Elektrik-Elektronik Mühendisliği
    We investigate the behavior of the power fluctuations of the focused annular and flat-topped beams when a realistic receiver possessing a finite sized aperture is employed in turbulent atmospheric optics links. Employing our previously derived formulation for the power scintillation index, the variations of the power scintillations and the receiver aperture averaging factor of the focused annular and flat-topped beams are scrutinized. Receiver aperture averaging factor is deduced from the ratio of power scintillation index detected by a finite sized aperture to that obtained by a point aperture. Influence of the receiver aperture radius, the propagation length, the structure constant, the inner and the outer beam sizes for an annular type incidence, flatness parameter for a flat-topped incidence and the focusing parameter for the multi-Gaussian beam in general, on the power scintillation and the receiver aperture averaging factor are studied. It is found that for the focused multi-Gaussian beams, the effect of the receiver aperture averaging factor increases as the aperture radius increases for larger link lengths. Additionally, for the annular incidences in turbulence, the effect of the receiver aperture averaging factor is stronger for larger inner beam source sizes. At a fixed receiver aperture radius, receiver aperture averaging becomes more effective when the structure constant becomes larger. When focused multi-Gaussian beams are compared to their collimated counterparts, it is seen that the receiver aperture averaging is more beneficial for the focused annular and focused flat-topped beams. At large link lengths, increase in the receiver aperture radius decreases the power scintillations.
  • Conference Object
    Citation - WoS: 2
    Diffraction Properties of Partially Coherent Elegant High-Order Beam
    (Electromagnetics Acad, 2010) Eyyuboğlu, Halil Tanyer; Wang, Fei; Baykal, Yahya Kemal; Cai, Yangjian; Eyyuboglu, Halil T.; Baykal, Yahya; Elektronik ve Haberleşme Mühendisliği; Elektrik-Elektronik Mühendisliği
    The diffraction properties of a partially coherent elegant higher-order beam in free space are investigated in detail. It is found that the diffraction properties of a partially coherent elegant higher-order beam upon propagation are closely related to its initial coherence. A partially coherent elegant higher-order beam spreads more slowly than a partially coherent standard higher-order beam, which has potential application in free-space optical communications.
  • Conference Object
    Effects of Focusing on Scintillations of Higher Order Laser Modes in Non-Kolmogorov Turbulence
    (Electromagnetics Acad, 2014) Baykal, Yahya Kemal; Baykal, Yahya; Elektrik-Elektronik Mühendisliği
    The scintillation index of focused higher order laser beam propagating in non-Kolmogorov atmospheric turbulence is formulated by employing the Rytov method and the equivalence of the structure constant. Our evaluations are performed for even modes. The equivalence formula for the structure constant is extracted from our earlier work in which the equivalence is obtained by equating the scintillation indices found in the Kolmogorov and the non-Kolmogorov turbulence. If not specified otherwise, the focused beam is defined when the focal length is equal to the link length. For the focused higher order laser beams, as the power law exponent of the non-Kolmogorov spectrum decreases, the scintillations decrease. At any power law exponent, the scintillations tend to become larger when the mode order of the focused beam becomes larger, i.e., the focused Gaussian beam is advantageous over the focused higher order laser beams for any realization of the non-Kolmogorov turbulence. Again being valid for any power law exponent, increase in the source size is found to decrease the intensity fluctuations of all the focused higher order mode scintillations. Especially for the larger order beams, focusing the higher order beam at a distance smaller than the link length results in a change in the behaviour of the scintillation index versus the power law exponent. In such cases, the scintillations are observed to increase. Comparison of the focused higher order beam scintillations with the previously obtained collimated higher order beam scintillations yields that the focused higher order beam scintillations are lower. Collimated higher order beams exhibit lower scintillations than the collimated Gaussian beams whereas this is reversed in the focused case. Another observation in such comparison shows that the difference of the intensity fluctuations between the Gaussian and the higher order beams are much larger in the focused case, especially at larger power law exponent values.