Browsing by Author "Gercekcioglu, Hamza"

Now showing 1 - 20 of 31

Citation - WoS: 69
Citation - Scopus: 74
Equivalence of Structure Constants in Non-Kolmogorov and Kolmogorov Spectra
(Optical Soc Amer, 2011) Baykal, Yahya; Gercekcioglu, Hamza
We find the equivalence of the structure constants in non-Kolmogorov and Kolmogorov spectra in a turbulent atmosphere. As the reference point, the spherical wave scintillation index in a non-Kolmogorov medium is used. Relations of the structure constants are found to be functions of the power law of the turbulence spectrum and the Fresnel zone. It will be useful to employ the equivalence of the structure constants in making performance comparisons found with non-Kolmogorov and Kolmogorov spectra. (C) 2011 Optical Society of America
Citation - WoS: 3
Citation - Scopus: 3
Laser Beam Scintillations of Lidar Operating in Weak Oceanic Turbulence
(Optica Publishing Group, 2022) Baykal, Yahya; Gercekcioglu, Hamza
The formulation of light detection and ranging (LIDAR) systems is derived and examined for the scintillation index, evaluated on-axis, of laser beams in horizontal links in the ocean with weak turbulence by utilizing the Rytov method. These scintillation indices, obtained for the Gaussian beam which is collimated, the limits of plane and spherical waves, are depicted versus the source size, target size, and parameter of the normalized reflector size. It is found that the source size, target size, and normalized reflector size parameter, lessening the scintilla-tion index evaluated on-axis, are approximately 0.44 cm, 56 x 10-4 cm, and 2.2, respectively. Additionally, by using these values that minimize the scintillation index, the variation of the scintillations is shown against the propagation distance, radius of reflector, temperature and salinity fluctuation effects, mean squared temperature, and turbulent kinetic energy dissipation rate per unit mass of fluid at various selected source size and radius of reflector values. (c) 2022 Optica Publishing Group
Citation - WoS: 24
Citation - Scopus: 23
Scintillation Index of Flat-Topped Gaussian Laser Beam in Strongly Turbulent Medium
(Optical Soc Amer, 2011) Gercekcioglu, Hamza; Baykal, Yahya
In a strongly turbulent medium, the scintillation index of flat-topped Gaussian beams is derived and evaluated. In the formulation, unified solution of Rytov method is utilized. Our results correctly reduce to the existing strong turbulence scintillation index of the Gaussian beam, and naturally to spherical and plane wave scintillations. Another checkpoint of our result is the scintillation index of flat-topped Gaussian beams in weak turbulence. Regardless of the order of flatness, scintillations of flat-topped Gaussian beams in strong turbulence are found to be determined mainly by the small-scale effects. For large-sized beams in moderate and strongly turbulent medium, flatter beams exhibit smaller scintillations. (C) 2011 Optical Society of America
Citation - WoS: 4
Citation - Scopus: 1
Intensity Fluctuations of Flat-Topped Beam in Non-Kolmogorov Weak Turbulence: Reply
(Optical Soc Amer, 2012) Gercekcioglu, Hamza; Baykal, Yahya
In our recent publication, we have examined the intensity fluctuations of flat-topped beam in non-Kolmogorov weak turbulence [J. Opt. Soc. Am. A 29, 169 (2012)] in which our comparison of the scintillation indices in the Kolmogorov and in various non-Kolmogorov turbulences was based on the same structure constant, no matter what power law the non-Kolmogorov spectrum takes. In such choice of the fixed structure constant, which is also being used by many researchers in the field [Opt. Express 18, 451 (2010); Proc. SPIE 6747, 67470B (2007); Opt. Commun. 285, 880 (2012)], we have found that the variation of the scintillation index against non-Kolmogorov power law exhibits a peak at the worst power law, which happens to be smaller than the Kolmogorov power law of 11/3. Charnotskii commented [J. Opt. Soc. Am. A. 29, 1838 (2012)] on our paper. In this paper, in our to reply to Charnotskii's comment, we have re-evaluated the scintillation index of flat-topped beam in non-Kolmogorov weak turbulence by employing our recently reported equivalent structure constant [Opt. Lett. 36, 4554 (2011)] and re-compared the intensity fluctuations in Kolmogorov and in non-Kolmogorov turbulences. As the result of such re-comparison, the worst power law is observed to disappear. c 2012 Optical Society of America
Citation - WoS: 4
Citation - Scopus: 3
Intensity and Degree of Coherence of Vortex Beams in Atmospheric Turbulence
(Ieee-inst Electrical Electronics Engineers inc, 2024) Gokce, Muhsin Caner; Baykal, Yahya; Gercekcioglu, Hamza; Ata, Yalcin
We utilize the Huygens-Fresnel principle to derive the mutual coherence function (MCF) for a vortex beam, which is the main focus of our investigation. Then, we examine the intensity and modulus of the complex degree of coherence (DOC) characteristics of vortex beams in atmospheric turbulence. Our results indicate that as the topological charge increases, the intensity distribution of the vortex beam becomes less affected by atmospheric turbulence. However, the modulus of the complex DOC decreases.
Citation - WoS: 4
Citation - Scopus: 6
Scintillation of Laser Beams in Weak Atmospheric Turbulence for Aerial Vehicle in the Use of Lidar
(Ieee-inst Electrical Electronics Engineers inc, 2022) Baykal, Yahya; Gercekcioglu, Hamza
Formulation of on-axis scintillation of laser beams is found in weak atmospheric turbulence for aerial vehicle in the use of light detection and ranging (LIDAR) systems by employing the Rytov method. The formulation derived for collimated Gaussian, plane and spherical beams is evaluated in vertical link involving up/down link. In this medium, the behavior of these beams in terms of deterioration is examined. In this context, the on-axis scintillation index values are plotted versus normalized target size parameter, target size, source size, propagation distance and zenith angle, and the results are obtained for LIDAR systems operating for aerial vehicle in vertical atmospheric link by using ground/space transceiver. The degradation is greater in operating with ground transceiver than in operating with space transceiver. Additionally, while the on-axis scintillation index is minimized in the smaller target size in use of ground transceiver than in use of space transceiver, that is, it can also be minimized in the larger target size in use of space transceiver. The values of source size and the normalized target size parameter minimizing the obtained scintillation index, are 1.2 cm, 10, and 6 cm and 5 for ground transceiver and space transceiver, respectively.
Citation - WoS: 1
Citation - Scopus: 1
Scintillations of Higher-Order Optical Beams in Biological Tissues
(Optica Publishing Group, 2025) Baykal, Yahya; Gokce, Muhsin Caner; Ata, Yalcin; Gercekcioglu, Hamza
The Scintillation index of a higher-order laser beam in turbulent biological tissue is formulated and evaluated. Behaviors of the scintillation indices of various higher-order beams against the tissue turbulence parameters of the strength coefficient of the refractive index fluctuations, fractal dimension, characteristic length of heterogeneity, small length-scale factor, and the source size, tissue length, and wavelength are examined. Fluctuations in the intensity are also investigated when various types of tissues, such as the intestinal epithelium (mouse), liver parenchyma (mouse), and upper dermis (human), are excited by different higher-order laser beams. (c) 2025 Optica Publishing Group. All rights, including for text and data mining (TDM), Artificial Intelligence (AI) training, and similar technologies, are reserved.
Citation - WoS: 5
Minimization Effects on Scintillations of Sinusoidal Gaussian Beams in Strong Turbulence
(Iop Publishing Ltd, 2011) Gercekcioglu, Hamza; Baykal, Yahya
Minimization effects on the on-axis scintillation index of cos Gaussian (cG) and cosh Gaussian (chG) beams are studied in strong turbulence. In our formulation, the unified solution of the Rytov method, which imposes spatial filtering to extend the solution to the strong turbulence regime, is applied. Our solution correctly reduces to the weak turbulence sinusoidal beam scintillations and the strong turbulence Gaussian beam scintillations. The conditions to minimize the scintillations are found to be focused chG beams. Small scale scintillations mainly determine the overall scintillations of cG and chG beams in strong turbulence. In strong turbulence, increase in the source size decreases the scintillations of collimated cG beams but does not change the scintillations of focused cG beams. Collimated cG beams having larger displacement parameters and large focal lengths show smaller scintillations in the strong regime. Change in the displacement parameters for collimated and focused chG beams and the focal length of focused chG beams do not considerably vary their scintillations in strong turbulence.
Citation - WoS: 3
Citation - Scopus: 3
Field Correlations of Multimode Optical Beams in Underwater Turbulence
(Optica Publishing Group, 2024) Baykal, Yahya; Gokce, Muhsin C.; Ata, Yalcin; Gercekcioglu, Hamza
For multimode optical beams, field correlations at the receiver plane are found in underwater turbulence. Field correlations of single high order beams in underwater turbulence are special cases of our formulation. Variations of field correlations against the underwater turbulence parameters and the diagonal length from various receiver points are examined for different multimode and single high order beams. Stronger underwater turbulence is found to reduce the field correlations of multimode and single high order optical beams. The results will be of help in heterodyne detection analysis and fiber coupling efficiency in an underwater medium experiencing turbulence. (c) 2024 Optica Publishing Group
Citation - WoS: 18
Citation - Scopus: 18
Minimization of Scintillation Index Against Displacement Parameters
(Elsevier Science Bv, 2008) Eyyuboglu, Halil T.; Gercekcioglu, Hamza; Baykal, Yahya
For 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.
Citation - WoS: 19
Citation - Scopus: 18
Average Transmittance in Non-Kolmogorov Turbulence
(Elsevier Science Bv, 2013) Ata, Yalcin; Baykal, Yahya; Gercekcioglu, Hamza
Average transmittance in non-Kolmogorov turbulence is evaluated. Our recently published equivalent structure constant formulation is employed in our numerical evaluations. At the fixed propagation distance and wavelength, and at the corresponding equivalent structure constant, as the power law exponent of the non-Kolmogorov spectrum increases, the on-axis transmittance is found to decrease. At the same power law exponent of the non-Kolmogorov spectrum, the off-axis transmittance is obtained to be smaller than the on-axis transmittance. Off-axis transmittance variation versus the power law exponent shows that similar to the on-axis case, increase in the power law exponent eventually causes the off-axis transmittance to decrease, however this decrease occurs at larger power law exponent for larger off-axis distance. (C) 2013 Elsevier B.V. All rights reserved.
Citation - WoS: 32
Citation - Scopus: 32
Ber of Annular and Flat-Topped Beams in Non-Kolmogorov Weak Turbulence
(Elsevier, 2013) Gercekcioglu, Hamza; Baykal, Yahya
The average bit error rate (BER) of multi-Gaussian beams in non-Kolmogorov weak turbulence is examined. For each specific incidence of annular and flat-topped optical beam, a power law of non-Kolmogorov spectrum is found which is defined as the worst power law at which the average BER attains the maximum value. Using these values of the worst power laws, it is observed that thinner collimated annular, larger focal length annular and flatter small sized collimated flat-topped structures have a slight advantage in obtaining smaller average BER. (C) 2012 Elsevier B.V. All rights reserved.
Citation - WoS: 5
Citation - Scopus: 5
Minimization of the Scintillation Index of Sinusoidal Gaussian Beams in Weak Turbulence for Aerial Vehicle-Satellite Laser Communications
(Optical Soc Amer, 2021) Gercekcioglu, Hamza; Baykal, Yahya
Minimization of the on-axis scintillation index of sinusoidal Gaussian beams is investigated by using the modified Rytov method in weak atmospheric turbulence for uplink/downlink of aerial vehicle-satellite laser communications. Among the focused cosh-Gaussian (cosh-G), cos-Gaussian (cos-G), annular, and Gaussian beams, a suitable displacement parameter for a cosh-G beam is determined that will minimize the scintillation index in uplink and downlink configurations. Then, for both uplink and downlink, the variations of the scintillation index against the propagation distance, source size, and zenith angle are examined and compared among themselves to show the optimum beam that possesses the minimum scintillation index. Sinusoidal Gaussian beams that are focused at the receiver and obtained by employing the appropriate displacement parameter, which we name the optimum beams, are recommended to obtain smaller intensity fluctuations in atmospheric wireless optical communication systems operating in vertical links in weak turbulence. (C) 2021 Optical Society of America
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.
Citation - Scopus: 1
Multimode Laser Beam Field Correlations for Vertical Links Operating in Oceanic Turbulence
(IEEE-Inst Electrical Electronics Engineers inc, 2025) Gercekcioglu, Hamza; Baykal, Yahya; Gokce, Muhsin Caner
In underwater optical vertical link medium, based on the extended Huygens-Fresnel principle, multimode laser beam field correlation is derived and evaluated analytically in the Atlantic Ocean at high latitude and high latitude- low latitudes. With the depth of seawater, the coherence length of a spherical wave operating in the underwater turbulent medium is demonstrated for the range of 0-4000 m. By utilizing the coherence length varying with parameters such as the rate of dissipation of turbulent kinetic energy per unit mass of fluid epsilon, the rate of dissipation of the mean squared temperature chi(T) and non-dimensional representing the relative strength of temperature and salinity fluctuations omega, which depend on depth, the field correlation is examined in detail for single modes and multimode. Their variations are exhibited. Our results indicate clearly that as the mode increases, field correlation gets better.
Citation - WoS: 7
Citation - Scopus: 9
Multimode Laser Beam Scintillations in Weak Atmospheric Turbulence for Vertical Link Laser Communications
(Taylor & Francis Ltd, 2022) Sayan, Omer F.; Gercekcioglu, Hamza; Baykal, Yahya
Scintillation index of multimode laser beams used for communication systems in vertical paths of weak atmospheric turbulent medium are examined by employing the Rytov method. On-axis scintillation index is examined versus the source size, propagation distance and zenith angle for vertical link including uplink and downlink. At the selected values of source sizes and propagation distances, scintillation responses of multimode laser beams are evaluated. In general, it is found for both uplink and downlink that the laser beam with multimode content has larger scintillation noise as compared to a Gaussian laser beam. However, for the downlink at L=700 km, at the chosen parameters, the multimode beam possessing larger mode content, is found to attain slightly smaller scintillations.
Citation - WoS: 18
Citation - Scopus: 16
Ber of Annular and Flat-Topped Beams in Strong Turbulence
(Elsevier, 2013) Gercekcioglu, Hamza; Baykal, Yahya
The average bit error rate (< BER >) of annular and flat-topped beams are evaluated in strong turbulence. In this respect, our earlier results on the scintillation indices obtained by the unified Rytov method are employed and the intensity is taken to be gamma-gamma distributed. For comparison purposes, < BER > for the log-normal intensity distribution is also evaluated. It is found that for the annular beams, the ones that are thinner, possessing smaller ratio of primary to secondary beam size, and smaller focal lengths will have smaller average BER in strong turbulence. For the flat-topped beams, the ones that are flatter and possessing large source sizes have smaller average BER in strong turbulence. Large average SNR substantially reduces the average BER in weak and moderate turbulence, whereas in strong turbulence, the average BER stays at the same value no matter what the average SNR is. Comparison of the log-normal and the gamma-gamma statistics for the intensity shows that the average BER will be higher for the log-normal case when the average SNR is small and the reverse relationship holds at large average SNR. For both the gamma-gamma and the log-normal intensity distributions, < BER > obtained for the annular and the, flat-topped beams in strong turbulence is advantageous over the Gaussian beam < BER > values. (C) 2013 Elsevier B.V. All rights reserved.
Citation - WoS: 7
Citation - Scopus: 8
Field Correlations of Partially Coherent Optical Beams in Underwater Turbulence
(Optica Publishing Group, 2022) Baykal, Yahya; Gercekcioglu, Hamza
Field correlations of partially coherent optical beams at the receiver plane are formulated and evaluated in underwater turbulence. Variations of the field correlations are examined against changes in the degree of source coherence, diagonal length from the receiver point, receiver point, propagation distance, source size, ratio of temperature to salinity contributions to the refractive index spectrum, rate of dissipation of mean-squared temperature, and rate of dissipation of kinetic energy per unit mass of fluid. Under any underwater turbulence and link conditions, it is found that field correlations at the receiver plane reduce when the optical source becomes less coherent. (c) 2022 Optica Publishing Group
Citation - WoS: 37
Citation - Scopus: 44
Annular Beam Scintillations in Strong Turbulence
(Optical Soc Amer, 2010) Gercekcioglu, Hamza; Baykal, Yahya; Nakiboglu, Cem
A scintillation index formulation for annular beams in strong turbulence is developed that is also valid in moderate and weak turbulence. In our derivation, a modified Rytov solution is employed to obtain the small-scale and large-scale scintillation indices of annular beams by utilizing the amplitude spatial filtering of the atmospheric spectrum. Our solution yields only the on-axis scintillation index for the annular beam and correctly reduces to the existing strong turbulence results for the Gaussian beam-thus plane and spherical wave scintillation indices-and also correctly yields the existing weak turbulence annular beam scintillations. Compared to collimated Gaussian beam, plane, and spherical wave scintillations, collimated annular beams seem to be advantageous in the weak regime but lose this advantage in strongly turbulent atmosphere. It is observed that the contribution of annular beam scintillations comes mainly from the small-scale effects. At a fixed primary beam size, the scintillations of thinner collimated annular beams compared to thicker collimated annular beams are smaller in moderate turbulence but larger in strong turbulence; however, thinner annular beams of finite focal length have a smaller scintillation index than the thicker annular beams in strong turbulence. Decrease in the focal length decreases the annular beam scintillations in strong turbulence. Examining constant area annular beams, smaller primary sized annular structures have larger scintillations in moderate but smaller scintillations in strong turbulence. (C) 2010 Optical Society of America
Citation - WoS: 32
Citation - Scopus: 36
Hermite Gaussian Beam Scintillations in Weak Atmospheric Turbulence for Aerial Vehicle Laser Communications
(Elsevier, 2020) Sayan, Omer F.; Gercekcioglu, Hamza; Baykal, Yahya
Scintillation index of Hermite Gaussian beams used for air vehicle communication systems in vertical paths of weak atmospheric turbulent medium are investigated by employing the modified Rytov method. By evaluating the on-axis scintillation index, variations of the scintillation indices of these beams are examined against the changes in the Gaussian beam size of the Hermite Gaussian beam mode, propagation distances and the zenith angles at the realistic propagation distances involved in uplink and downlink configurations. In the atmospheric environment, for uplink, the Hermite Gaussian beam modes have no advantage over the Gaussian beams at short propagation distances like L = 20 km,as well as at long propagation distances like L = 700 km. However, for downlink, although Hermite Gaussian beam modes are disadvantageous over the Gaussian beams at short propagation distances like L = 20 km, they are found advantageous over the Gaussian beams at long propagation distances like L = 700 km. The results of this study may encourage to use Hermite Gaussian beams, especially in the air vehicle laser communication links, and can be used in the design of an optical wireless communication link utilizing the vertical atmospheric medium.