Optik 125 (2014) 561–564 Contents lists available at ScienceDirect Optik jou rn al homepage: www.elsevier.de/ijleo Beam wander of electromagnetic partially coherent flat-topped beam propagating in turbulent atmosphere Mehdi Sharifi a , Guohua Wu b , Bin Luo a , Anhong Dang a , Hong Guo a,∗ a The State Key Laboratory of Advanced Optical Communication Systems and Networks and Institute of Quantum Electronics, School of Electronics Engineering and Computer Science, Peking University, Beijing 100871, China b School of Electronic Engineering, Beijing University of Posts and Telecommunications, Beijing 100876, China a r t i c l e i n f o Article history: Received 2 March 2013 Accepted 3 July 2013 Keywords: Electromagnetic flat-topped beam Beam wander Turbulent atmosphere a b s t r a c t Beam wander of an electromagnetic partially coherent flat-topped (EPCFT) beam propagating through turbulent atmosphere is studied. The analytical expression of beam wander effect is obtained. The influ- ence of source size, source spatially coherent lengths, degree of polarization, and beam flatness order are studied in detail. It has been shown that by adjusting these parameters appropriately, the beam wander effects could be greatly reduced. Compared with increasing the degree of polarization, the beam wander could be reduced much more effectively by increasing the beam flatness order. The EPCFT beam can greatly reduce the beam wander effect and the parameters should be chosen very carefully for different applications. © 2013 Elsevier GmbH. All rights reserved. 1. Introduction Beam wandering is one of the most important effects of the atmospheric turbulence that limits the use of the FSO communica- tion systems. Beam wander which is caused mostly by large-scale turbulence near the transmitter, can be defined as the combined effect of the movement of the short-term beam centroid in the receiver plane and the movement of the short-term beam instan- taneous center around the beam centroid within the beam [1,2]. Up to now, beams wander for a variety of beams with different shapes, such as, dark hollow, annular, and cos and cosh-Gaussian and flat-topped beam have been studied [3–6]. These researches indicate that under certain condition, above mentioned beams, can show less beam wander compared with a fundamental Gaussian beam. Many results indicate that partially coherent beams can effec- tively reduce intensity fluctuation and consequently improve the performance of the laser communication systems [7–9]. In this regards, partially coherent flat-topped (PCFT) beams with wide applications has attracted considerable attention in recent years. Propagation properties of different kinds of PCFT beams in atmo- spheric turbulence have been investigated [10–14]. On the other hand, an electromagnetic partially polarized beam characterized by its polarization properties can further reduce the scintillation index more compared with linearly polarized beams ∗ Corresponding author. Tel.: +86 10 62753208. E-mail address: hongguo@pku.edu.cn (H. Guo). [15]. As a result and due to practical importance of this kind of beams, the propagation properties of electromagnetic partially polarized beams propagating through atmospheric turbulence has attracted considerable attention in recent years [16–23]. As indicated by previous researches [3], flat-topped beams exhibit less beam wander with respect to a fundamental Gaussian beam. Thus, it is valuable the studying of the beam wander of a partially polarized EPCFT beam. The aim is to investigate how the coherence and polarization aspects as well as beam flatness order can affect on beam wander of EPCFT beam. In this paper we extend the general model of beam wander, to the case of an electromagnetic partially coherent flat-topped (EPCFT) beam. In next sections, a general expression of the beam wander is derived for an EPCFT beam. Then beam wander expres- sion is examined by numerical examples and figures in which the effects of source size, source coherence lengths, degree of polariza- tion and order of flatness are also studied in detail. 2. Theoretical model Beam wander can be expressed as variance random displace- ment (r c ) of the instantaneous center of the beam as it propagates through atmospheric turbulence as [1] r 2 c  = 4 2 k 2 W 2 FS (L)  L 0  ∞ 0 ˚ n ()H LS (, z) ×  1 − exp  − L 2 (1 − z/L) 2 k  ddz, (1) 0030-4026/$ – see front matter © 2013 Elsevier GmbH. All rights reserved. http://dx.doi.org/10.1016/j.ijleo.2013.07.025