Browsing by Author "Cai, Y."

Now showing 1 - 19 of 19

Citation - WoS: 71
Citation - Scopus: 78
Average intensity and spreading of partially coherent standard and elegant Laguerre-Gaussian beams in turbulent atmosphere
(Emw Publishing, 2010) Wang, F.; Cai, Y.; Eyyuboglu, H. T.; Baykal, Y.; 7688; 7812
Analytical expressions for the average intensity, mean-squared beam width and angular spread of partially coherent standard and elegant Laguerre-Gaussian (LG) beams propagating in turbulent atmosphere are derived. The properties of the average intensity, spreading and directionality of partially coherent standard and elegant LG beams in turbulent atmosphere are studied numerically and comparatively. It is found that the beam parameters and structure constant of turbulence together determine the properties of the beams in turbulent atmosphere. Partially coherent standard and elegant LG beams with smaller coherence length, larger beam orders and longer wavelength are less affected by the turbulence. A partially coherent elegant LG beam is less affected by turbulence than a partially coherent standard LG beam under the same condition. Furthermore, it is found that there exist equivalent partially coherent standard and elegant LG beams, equivalent fully coherent standard and elegant LG beams, equivalent Gaussian Schell-model beams that may have the same directionality as a fully coherent Gaussian beam both in free space and in turbulent atmosphere. Our results will be useful in long distance free-space optical communications.
Citation - WoS: 26
Citation - Scopus: 26
Beam wander characteristics of cos and cosh-Gaussian beams
(Springer, 2009) Cil, C. Z.; Çil, Celal Zaim; Eyyuboglu, H. T.; Baykal, Y.; Cai, Y.; 7688; 7812; Elektronik ve Haberleşme Mühendisliği
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.
Beam wander of J (0)- and I (0)-Bessel Gaussian beams propagating in turbulent atmosphere
(2010) Çil, Celal Zaim; Baykal, Yahya Kemal; Baykal, Yahya Kemal; Korotkova, O.; Cai, Y.; 7812; Elektronik ve Haberleşme Mühendisliği; Elektrik-Elektronik Mühendisliği
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.
Citation - WoS: 26
Citation - Scopus: 27
Beam Wander of J (0)- and I (0)-Bessel Gaussian Beams Propagating In Turbulent Atmosphere
(Springer, 2010) Cil, C. Z.; Çil, Celal Zaim; Eyyuboglu, H. T.; Baykal, Y.; Korotkova, O.; Cai, Y.; 7812; 7688; Elektronik ve Haberleşme Mühendisliği
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.
Beam wander of J 0- and i 0-Bessel Gaussian beams propagating in turbulent atmosphere
(2010) Çil, C.Z.; Eyyuboğlu, H.T.; Baykal, Y.; Korotkova, O.; Cai, Y.; 7812
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.
Citation - WoS: 13
Citation - Scopus: 17
Correlation properties of random electromagnetic beams in laser resonators
(Springer Heidelberg, 2009) Tong, Z.; Korotkova, O.; Cai, Y.; Eyyuboglu, H. T.; Baykal, Y.; 7688; 7812
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.
Citation - WoS: 59
Citation - Scopus: 64
Degree of polarization for partially coherent general beams in turbulent atmosphere
(Springer, 2007) Eyyuboglu, H. T.; Baykal, Y.; Cai, Y.; 7688; 7812
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.
Citation - WoS: 1
Citation - Scopus: 0
Formulation of scintillations for optical incidence of arbitrary field profile
(Electromagnetics Acad, 2008) Baykal, Y.; Eyyuboglu, H. T.; Cai, Y.; 7812; 7688
Scintillation 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.
Citation - WoS: 57
Citation - Scopus: 62
Intensity fluctuations in J-Bessel-Gaussian beams of all orders propagating in turbulent atmosphere
(Springer, 2008) Eyyuboglu, H. T.; Sermutlu, Emre; Sermutlu, E.; Baykal, Y.; Cai, Y.; Korotkova, O.; 7688; 17647; 7812; Matematik
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.
Citation - WoS: 12
Citation - Scopus: 17
Partially coherent elegant Hermite-Gaussian beam in turbulent atmosphere
(Springer, 2011) Wang, F.; Cai, Y.; Eyyuboglu, H. T.; Baykal, Y.; 7688; 7812
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.
Citation - WoS: 12
Citation - Scopus: 14
Partially coherent elegant Hermite-Gaussian beams
(Springer Heidelberg, 2010) Wang, F.; Çil, Celal Zaim; Cai, Y.; Eyyuboglu, H. T.; Baykal, Y.; Cil, C. Z.; 7688; 7812; Elektronik ve Haberleşme Mühendisliği
Elegant Hermite-Gaussian beams (EHGBs) are extended to the partially coherent case. An explicit and analytical formula is derived for the cross-spectral density of a partially coherent EHGB propagating through an aligned or misaligned paraxial ABCD optical system. The propagation properties of a partially coherent EHGB in free space and its focusing properties through a thin lens are studied numerically, and are compared to those of a partially coherent standard Hermite-Gaussian beam (SHGB). It is found that the propagation and focusing properties of a partially coherent EHGB are closely related to its initial coherence. A partially coherent EHGB spreads slower than a partially coherent SHGB in free-space propagation. A partially coherent EHGB can be focused more tightly than a partially coherent SHGB.
Citation - WoS: 131
Citation - Scopus: 151
Propagation of laser array beams in a turbulent atmosphere
(Springer Heidelberg, 2007) Cai, Y.; Chen, Y.; Eyyuboglu, H. T.; Baykal, Y.; 7688; 7812
The propagation of phase-locked and non-phase-locked laser array beams of radial and rectangular symmetries in a turbulent atmosphere are investigated based on the extended Huygens-Fresnel integral. The beamlet used in our paper for constructing the laser array beams is of elliptical Gaussian mode. Analytical formulae for the average irradiance of phase-locked and non-phase-locked radial and rectangular laser array beams are derived through vector integration and tensor operation. The irradiance properties of these laser array beams in a turbulent atmosphere are studied numerically. It is found that both phase-locked and non-phase-locked radial and rectangular laser array beams eventually become circular Gaussian beams in a turbulent atmosphere, which is much different from their propagation properties in free space. The propagation properties are closely related to the parameters of laser array beams and the structure constant of the turbulent atmosphere.
Citation - WoS: 0
Citation - Scopus: 0
Propagation of partially coherent beams after a source plane ring aperture
(Electromagnetics Acad, 2008) Eyyuboglu, H. T.; Baykal, Y. K.; Cai, Y.; 7688; 7812
The 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.
Citation - WoS: 36
Citation - Scopus: 37
Scintillation advantages of lowest order Bessel-Gaussian beams
(Springer Heidelberg, 2008) Eyyuboglu, H. T.; Sermutlu, Emre; Baykal, Y.; Sermutlu, E.; Cai, Y.; 7688; 7812; 17647; Matematik
For a weak turbulence propagation environment, the scintillation index of the lowest order Bessel-Gaussian beams is formulated. Its triple and single integral versions are presented. Numerical evaluations show that at large source sizes and large width parameters, when compared at the same source size, Bessel-Gaussian beams tend to exhibit lower scintillations than the Gaussian beam scintillations. This advantage is lost however for excessively large width parameters and beyond certain propagation lengths. Large width parameters also cause rises and falls in the scintillation index of off-axis positions toward the edges of the received beam. Comparisons against the fundamental Gaussian beam are made on equal source size and equal power basis.
Citation - WoS: 21
Citation - Scopus: 22
Scintillation 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.; 7688; 7812
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.
Citation - WoS: 75
Citation - Scopus: 81
Scintillation properties of dark hollow beams in a weak turbulent atmosphere
(Springer Heidelberg, 2008) Chen, Y.; Cai, Y.; Eyyuboglu, H. T.; Baykal, Y.; 7688; 7812
The on-axis scintillation index for a circular dark hollow beam (DHB) propagating in a weak turbulent atmosphere is formulated, and the scintillation properties of a DHB are investigated in detail. The scintillation index for a DHB reduces to the scintillation index for a Gaussian beam, an annular beam and a flat-topped beam under certain conditions. It is found that the scintillation index of a DHB is closely related to the beam parameters and can be lower than that of a Gaussian beam, an annular beam and a flat-topped beam in a weak turbulent atmosphere at smaller waist sizes and longer propagation lengths.
Citation - WoS: 1
Citation - Scopus: 1
Scintillations in weak turbulence of annular beams whose individual components are incoherent
(Electromagnetics Acad, 2010) Baykal, Y.; Eyyuboglu, H. T.; Cai, Y.; 7812; 7688
The scintillation index, arising from the intensity fluctuations in weak atmospheric turbulence of annular beams whose individual components are incoherent, is formulated. For such beams whose annularities are obtained by varying the source sizes and magnitudes of the individual beams, evaluations show that at very small sized beam structures, thinner beams possess smaller scintillations. As the sizes increase, the scintillation index values of thick and thin beams approach each other, eventually exhibiting the same scintillation behavior at large sized beam structures. Examination of the intensity fluctuations of the annular beams, whose individual incoherent components are at the same size but at different magnitudes, yield reverse behavior such that at very small sized beam structures, thicker beams possess smaller scintillations, however the scintillation values are very close to each other. Again, for large sized beams, the scintillation index values of thick and thin beams approach each other, eventually exhibiting the same scintillation behavior at large sized beam structures. Comparing the scintillation indices of annular beams whose individual components are incoherent to those of traditional annular beams of coherent components, it seems that for large sized beams, incoherently subtracted beams are advantageous, however the reverse is valid for very small sized beam structures.
Citation - WoS: 84
Citation - Scopus: 87
Scintillations of laser array beams
(Springer Heidelberg, 2008) Eyyuboglu, H. T.; Baykal, Y.; Cai, Y.; 7688; 7812
The scintillation index of a laser array beam is analytically derived and numerically evaluated for weak turbulence conditions. On-axis as well as off-axis positions of the receiver plane are considered. Our graphical illustrations prove that at longer propagation ranges and at some midrange radial displacement parameters, laser array beams exhibit less scintillations, when compared to a fundamental Gaussian beam. However, when compared among themselves, laser array beams tend to have reduced scintillations with rising numbers of beamlets, longer propagation wavelengths, at midrange radial displacement parameters, at intermediate Gaussian source sizes, at bigger inner scales and smaller outer scales of turbulence. However, in this improvement, the number of beamlets does not seem to have a major role.
Citation - WoS: 23
Citation - Scopus: 27
Spectral shifts of general beams in turbulent media
(Iop Publishing Ltd, 2008) Eyyuboglu, H. T.; Cai, Y.; Baykal, Y. K.; 7688; 7812
Using the concept of generalized beam, by applying the extended Huygens-Fresnel principle, we derive the spectrum for partially coherent cosh-Gaussian, cos-Gaussian, Gaussian and annular Gaussian beams propagating in turbulent media. From this formulation, graphical outputs are constructed illustrating the variation of receiver plane spectra against propagation distance, turbulence strength, degree of partial coherence and transverse coordinate. The dependence of spectral shifts on source and propagation parameters is observed. Spectrum invariance conditions are deduced analytically and discussed for the particular case of a fundamental Gaussian beam.