Elektronik ve Haberleşme Mühendisliği Bölümü Yayın Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/260
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Article Citation - WoS: 11Citation - Scopus: 12Changes of the Centroid Position of Laser Beams Propagating Through an Optical System in Turbulent Atmosphere(Elsevier Sci Ltd, 2013) Ji, Xiaoling; Baykal, Yahya; Jia, XinhongIn this paper, the effects of atmospheric turbulence, initial field amplitude, optical system and thermal blooming on the centroid position of laser beams propagating through the atmosphere are studied in detail. With the average over the ensemble of the turbulent medium, the centroid position is independent of turbulence. However, the centroid position depends on the centroid positions at the source plane and in the far-field, and the elements of ray-transfer-matrix. The physical reason why the centroid position changes on propagation is that the far-field centroid position is not located on the propagation z-axis due to the field phase distortion and the decentred intensity. The centroid position of laser beams with the spherical aberration and the decentred intensity is examined analytically. When laser beams with the decentred intensity propagate through the atmosphere, the effect of thermal blooming on the centroid position is investigated by using the four-dimensional (4D) computer code of the time-dependent propagation of high power laser beams through the atmosphere. (C) 2013 Elsevier Ltd. All rights reserved.Article Citation - WoS: 8Citation - Scopus: 9Scintillation Properties of a Truncated Flat-Topped Beam in a Weakly Turbulent Atmosphere(Elsevier Sci Ltd, 2013) Liu, Xianlong; Liang, Chunhao; Yuan, Yangsheng; Cai, Yangjian; Eyyuboglu, Halil T.We derive derive an explicit expression for the scintillation index of a truncated flat-topped (FT) beam in a weakly turbulent atmosphere. Under suitable conditions, the derived formula reduces to the expression for the scintillation index of a FT beam or Gaussian beam without truncation. The scintillation properties of a truncated FT beam in a weakly turbulent atmosphere are illustrated numerically. It is found that the truncation parameter has strong influence on the scintillation properties, and the advantage of a FT beam over a Gaussian beam for reducing the negative influence of turbulence disappears gradually as the truncation parameter decreases. (C) 2012 Elsevier Ltd. All rights reserved.Article Citation - WoS: 26Citation - Scopus: 33Propagation Factors of Hermite-Gaussian Beams in Turbulent Atmosphere(Elsevier Sci Ltd, 2010) Yuan, Yangsheng; Cai, Yangjian; Qu, Jun; Eyyuboglu, Halil T.; Baykal, YahyaBased on the extended Huygens-Fresnel integral and the second-order moments of the Wigner distribution function, an analytical formulae for the propagation factors (M-2-factors) of coherent and partially coherent one-dimensional Hermite-Gaussian beams in a turbulent atmosphere are derived. Evolution properties of the M-2-factor of the Hermite-Gaussian beam in a turbulent atmosphere are studied numerically in detail. Our results show that the M-2-factor of the Hermite-Gaussian beam increases upon propagation in a turbulent atmosphere. The M-2-factor of the Hermite-Gaussian beam with larger beam order (or lower coherence) increases slower that of the Hermite-Gaussian beam with smaller beam order (or higher coherence) in a turbulent atmosphere, which means that the Hermite-Gaussian beam with a larger beam order and lower coherence is less affected by a turbulent atmosphere. Our results will be useful in long-distance free-space optical communications. (c) 2010 Elsevier Ltd. All rights reserved.Article Citation - WoS: 7Citation - Scopus: 10Propagation of Various Dark Hollow Beams Through an Optical System in Turbulent Atmosphere(Elsevier Sci Ltd, 2010) Cai, Yangjian; Eyyuboglu, Halil T.; Baykal, Yahya; Eyyubolu, Halil T.The propagation of a dark hollow beam (DHB) of circular, elliptical or rectangular symmetry through aligned and misaligned ABCD optical systems in turbulent atmosphere is investigated. Analytical propagation formulae for the average intensities of various DHBs are derived based on the extended Huygens-Fresnel integral. As a numerical example, the focusing properties of various DHBs in turbulent atmosphere are studied It is found that the focusing properties of various DHBs in turbulent atmosphere are much different from their focusing properties in free space (C) 2010 Elsevier Ltd. All rights reserved.Article Citation - WoS: 76Citation - Scopus: 81Propagation and Coherence Properties of Higher Order Partially Coherent Dark Hollow Beams in Turbulence(Elsevier Sci Ltd, 2008) Eyyuboglu, Haill TanyerWe formulate and evaluate in terms of graphical outputs, source and receiver plane expressions, the complex degree of coherence, beam size variation and power in bucket performance for higher order partially coherent dark hollow beams propagating in turbulent atmosphere. Our formulation is able to cover square, rectangular, circular, elliptical geometries for dark hollow and flat-topped beams in one single expression. From the graphical outputs of the receiver plane, it is observed that higher order partially coherent dark hollow beams will initially develop an outer ring around a central lobe, but will eventually evolve towards a Gaussian shape as the propagation distance is extended. It is further observed that stronger turbulence levels and greater partial coherence have similar effects on beam profile. During propagation, modulus of complex degree of coherence of partially coherent dark hollow beams appears to rise above that of the source plane values, reaching as high as near unity. Beam size analysis shows that, among the types examined, (nearly) flat-topped beam experiences the least beam expansion. Power in bucket analysis indicates that lowest order square fully coherent dark beam offers the best power capturing. (c) 2007 Published by Elsevier Ltd.