Mode analysis of spreading of partially coherent beams propagating through atmospheric turbulence

Abstract

The spreading of partially coherent beams propagating through atmospheric turbulence is studied by use of the coherent-mode representation of the beams. Specifically, we consider partially coherent Gaussian Schell-model beams entering the atmosphere, and we examine the spreading of each coherent mode, represented by a Hermite-Gaussian function, on propagation. We find that in atmospheric turbulence the relative spreading of higher-order modes is smaller than that of lower-order modes, whereas the relative spreading of all order modes is the same as in free space. This modal behavior successfully explains why under certain circumstances partially coherent beams are less affected by atmospheric turbulence than are fully spatially coherent laser beams.

The Structure of Partially Coherent Fields

“…Gbur and Wolf (2002) looked theoretically at the spreading of partially coherent beams in random media, and noted that they are "resistant" to turbulence; this was demonstrated experimentally by Dogariu and Amarande (2003). Similar theoretical results were found by Ponomarenko, Greffet, and Wolf (2002) using a Hilbert-space method, and by Shirai et al (2003) using the coherent mode representation. Long-distance propagation of partially coherent beams was studied soon after by Salem, Shirai, Dogariu, and Wolf (2003).…”

“…A modal representation can also be applied to the propagation of fields through random media, as was demonstrated theoretically by Shirai, Dogariu, and Wolf (2003) in a study of the spreading of beams in turbulence. Schwartz and Dogariu (2006) have suggested that a modecoupling approach could be used to study more general properties of a turbulence-degraded beam.…”

Experimental determination of thermal turbulence effects on a propagating laser beam

“…Many theoretical and experimental investigations on the behavior of a propagating beam show Sphumelele C. Ndlovu: School of Chemistry and Physics, University of KwaZulu-Natal, Scottsville, Pietermaritzburg 3209, RSA *Corresponding Author: Naven Chetty: School of Chemistry and Physics, University of KwaZulu-Natal, Scottsville, Pietermaritzburg 3209, RSA, E-mail: ChettyN3@ukzn.ac.za that atmospheric turbulence leads to intensity perturbations [3][4][5][6][7][8][9]. These perturbations result from refractive index uctuations due to thermal uctuations in the atmosphere.…”

Optical coherenscopy based on phase-space tomography

“…A historical example illustrating the relevance of light statistics is found in astronomy where the star size was estimated from the measurement of the degree of coherence (DoC) [4]. Modern coherence-based techniques include ghost imaging [5,6], coherence controlled microscopy [7,8], lithography [9,10], and characterization of atmospheric [11] and plasma [12] instabilities. Moreover, the use of partially coherent light increases the transmission capacity of free-space communications [13] and improves information encoding [14].…”