Greg Gbur

Spreading of partially coherent beams in random media.

Some published computational work has suggested that partially coherent beams may be less susceptible to distortions caused by propagation through random media than fully coherent beams. In this paper this suggestion is studied quantitatively by examining the mean squared width of partially coherent beams in such media as a function of the propagation distance. The analysis indicates under what conditions, and to what extent, partially coherent beams are less affected by the medium.

Vortex beam propagation through atmospheric turbulence and topological charge conservation

The propagation of vortex beams through weak-to-strong atmospheric turbulence is simulated and analyzed. It is demonstrated that the topological charge of such a beam is a robust quantity that could be used as an information carrier in optical communications. The advantages and limitations of such an approach are discussed.

Phase singularities of the coherence functions in Young's interference pattern

We analyze the coherence properties of a partially coherent field emerging from two pinholes in an opaque screen and show that the spectral degree of coherence possesses phase singularities on certain surfaces in the region of superposition. To our knowledge, this is the first illustration of the singular behavior of the spectral degree of coherence, and the results extend the field of singular optics to the study of phase singularities of correlation functions.

Scintillation of Nonuniformly Polarized Beams in Atmospheric Turbulence

We demonstrate, through numerical simulations, that an appropriately chosen nonuniformly polarized coherent optical field can have appreciably smaller scintillation than comparable beams of uniform polarization. This results from the fact that a nonuniformly polarized field acts as an effective two-mode partially coherent field. The results described here are of direct relevance to the development of free-space optical communication systems.

Singular behavior of the spectrum in the neighborhood of focus.

In a recent paper [Phys. Rev. Lett. 88, 013901 (2002)] it was shown that when a convergent spatially coherent polychromatic wave is diffracted at an aperture, remarkable spectral changes take place on axis in the neighborhood of certain points near the geometrical focus. In particular, it was shown that the spectrum is red-shifted at some points, blueshifted at others, and split into two lines elsewhere. In the present paper we extend the analysis and show that similar changes take place in the focal plane, in the neighborhood of the dark rings of the Airy pattern.

The structure of partially coherent fields

Publisher Summary The general framework of optical coherence theory is now well established and has been described in numerous publications. This chapter provides an overview of recent advances, both theoretical and experimental, that have been made in a number of areas of classical optical coherence. These advances have been spurred on by the introduction of the space-frequency representation of partially coherent fields, and an increased emphasis on the spatial coherence properties of wave fields. The fundamental experiment to measure spatial coherence is Youngs double-slit experiment. A number of important optical processes are influenced by the coherence properties of the wave field. Results relating to the propagation of partially coherent wavefields highlight some of the significant results relating to optical beams. The influence of coherence on focusing is summarized and reviewed, along with the scattering of partially coherent wave fields and its relation to inverse scattering problems is discussed. It has been shown that spatial correlation functions have interesting topological properties associated with their phase singularities; these properties and the relevant literature are discussed. The coherent mode representation and its applications are described and several techniques for the numerical simulation of wave fields with a prescribed statistical behavior are explained.

Can spatial coherence effects produce a local minimum of intensity at focus

It is demonstrated that, for high-Fresnel-number focusing systems illuminated by certain classes of partially coherent light, it is possible to produce a local minimum of intensity at the geometrical focus. Such an effect is possible even though the average intensity in the entrance plane of the lens is uniform. An explanation is offered for this effect, and potential applications are considered.

Nonpropagating string excitations

It is shown that certain force distributions applied to a finite portion of an infinitely long string do not produce any excitation outside the region of the applied force. The existence of such nonpropagating excitations is demonstrated by a simple example, and two general theorems concerning their nature are proven. Some analogies between nonpropagating string excitations and fields produced by nonradiating sources are noted.

Partially coherent beam propagation in atmospheric turbulence [Invited]

Partially coherent beams hold much promise in free-space optical communications for their resistance to the deleterious effects of atmospheric turbulence. We describe the basic theoretical and computational tools used to investigate these effects, and review the research to date.

Determination of density correlation functions from scattering of polychromatic light

It is shown that for some many-particle systems with a high degree of symmetry, i.e. systems with homogeneous and/or isotropic density correlations, the density correlation function may be determined by measurements of the changes in the spectrum of polychromatic light scattered by the particles. The use of spectral measurements for such inverse problems may appreciably reduce the number of measurements required to uniquely determine the system structure.