Browsing by Author "Baykal, Y. K."

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Citation - WoS: 2
Citation - Scopus: 3
Method of Evaluation of the Mutual Coherence Function of Laser Beams and Its Application for Symmetric Dark Hollow Beams
(Spie-int Soc Optical Engineering, 2011) Banakh, V. A.; Marakasov, D. A.; Rytchkov, D. S.; Baykal, Y. K.; Eyyuboglu, T.; 7812
In our report, a method of evaluation of the mutual coherence function (MCF) of optical wave propagating in turbulent atmosphere is proposed. The method is based on using inverse Fresnel transform and 2-D Fast Fourier Transformation procedure (FFT) and provides a high accuracy in various propagation conditions from weak up to strong optical turbulence regime. This technique allows significantly reducing the evaluation time of MCF. The proposed method is suitable for optical waves with arbitrary initial distribution of amplitude and phase. Results of investigations on the degradation of coherence of symmetric dark hollow beams (DHB) propagating in turbulent atmosphere are presented. Analysis of evolution of MCF is brought up, and some characteristics of DHB, such as mean intensity distribution, and moments of Wigner distribution are calculated for various kinds of profiles of structural characteristic of refractive index. All of the evaluations for DHB are fulfilled for Kolmogorov spectrum of correlation function of refractive index fluctuations. The comparison between mean intensity calculations within the proposed method and method based on semi-analytical approach using of quadratic approximation of spherical wave structure function, is presented.
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: 23
Citation - Scopus: 23
Radius of curvature variations for annular, dark hollow and flat topped beams in turbulence
(Springer, 2010) Eyyuboglu, H. T.; Baykal, Y. K.; Ji, X. L.; 7688; 7812
For propagation in turbulent atmosphere, the radius of curvature variations for annular, dark hollow and flat topped beams are examined under a single formulation. Our results show that for collimated beams, when examined against propagation length, the dark hollow, flat topped and annular Gaussian beams behave nearly the same as the Gaussian beam, but have larger radius of curvature values. Increased partial coherence and turbulence levels tend to lower the radius of curvature. Bigger source sizes on the other hand give rise to larger radius of curvature. Dark hollow and flat topped beams have reduced radius of curvature at longer wavelengths, whereas the annular Gaussian beam seems to be unaffected by wavelength changes; the radius of curvature of the Gaussian beam meanwhile rises with increasing wavelength.
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.