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Greg Gbur

University of North Carolina at Charlotte, Physics and Optical Science, Department Member

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Greg Gbur is an Associate Professor of Physics and Optical Science at the University of North Carolina at Charlotte, specializing in classical theoretical optics (i.e. the wave properties of light). He has written a textbook on Mathematical Methods for Optical Physics and Engineering, published by Cambridge University Press in 2011. He also writes a blog on optics, physics, the history of science and horror fiction at skullsinthestars.com.
Phone: 704-687-8137
Address: UNC Charlotte
Department of Physics and Optical Science
9201 University City Blvd.
Charlotte, NC 28223

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Papers by Greg Gbur

S.M. Kim and G. Gbur, "Angular momentum conservation in partially coherent wavefields," Phys. Rev. A 86 (2012), 043814.

Angular momentum in electromagnetic wave systems is an important yet difficult subject to deal wi... more Angular momentum in electromagnetic wave systems is an important yet difficult subject to deal with, both classically and quantum mechanically. We investigate the angular momentum of partially coherent electromagnetic wave fields and establish the general formalism for angular momentum conservation, based on the Maxwell stress tensor for partially coherent sources and fields in the space-frequency domain. This formalism is applied to study the angular momentum properties of several classes of partially coherent electromagnetic beams possessing circulation.

Y. Gu and G. Gbur, "Reduction of turbulence-induced scintillation by nonuniformly polarized beam arrays," Opt. Lett. 37 (2012), 1553-1555.

We have explored a method to reduce turbulence-induced scintillation by using an incoherent beam ... more We have explored a method to reduce turbulence-induced scintillation by using an incoherent beam array composed of beamlets with nonuniform polarization. It is shown that significant scintillation reduction of such an incoherent beam array can be obtained by using nonuniformly polarized beamlets whose scintillation properties are optimized.

C. Rosenbury, G. Gbur and Y. Gu, "Phase singularities, correlation singularities, and conditions for complete destructive interference," J. Opt. Soc. Am. A 29 (2012), 410-416.

A previously derived condition for the complete destructive interference of partially coherent li... more A previously derived condition for the complete destructive interference of partially coherent light emerging from a trio of pinholes in an opaque screen is generalized to the case when the coherence properties of the field are asymmetric. It is shown by example that the interference condition is necessary, but not sufficient, and that the existence of complete destructive interference also depends on the intensity of light emerging from the pinholes and the system geometry; more general conditions for such interference are derived. The phase of the wave field exhibits both phase singularities and correlation singularities, and a number of nonintuitive situations in which complete destructive interference occurs are described and explained.

C.H. Gan, Y. Gu, T.D. Visser and G. Gbur, "Coherence converting plasmonic hole arrays," Plasmonics, 7 (2012), 313.

Simulations are presented that demonstrate that the global state of spatial coherence of an optic... more Simulations are presented that demonstrate that the global state of spatial coherence of an optical wavefield can be altered on transmission through an array of subwavelength-sized holes in a metal plate that supports surface plasmons. It is found that the state of coherence of the emergent field strongly depends on the separation between the holes and their scattering strength. Our findings suggest that subwavelength hole arrays on a metal film can be potentially employed as a plasmon-assisted coherence converting device, useful in modifying the directionality, spectrum, and polarization of the transmitted wave.

S. Sahin, G. Gbur and O. Korotkova, “Scattering of light from particles with semisoft boundaries,” Opt. Lett. 36 (2011), 3957-3959.

A three-dimensional multi-Gaussian function, being a finite sum of Gaussian functions, is adopted... more A three-dimensional multi-Gaussian function, being a finite sum of Gaussian functions, is adopted for modeling of a spherically symmetric scatterer with a semisoft boundary, i.e. such that has continuous and adjustable drop in the index of refraction. A Gaussian sphere and a hard sphere are the two limiting cases when the number of terms in multi-Gaussian distribution is one and infinity, respectively. The effect of the boundary's softness on the intensity distribution of the scattered wave is revealed. The generalization of the model to random scatterers with semisoft boundaries is also outlined.

X. Pang, G. Gbur and T.D. Visser, "The Gouy phase of Airy beams", Opt. Lett. 36 (2011), 2492-2494.

The phase behavior of Airy beams is studied, and their Gouy phase is defined. Analytic expression... more

G. Gbur, "Invisibility physics: Kerker's 'invisible bodies'", in B. Zivkovic, J. Goldman (Eds.), The Open Laboratory 2010 (Coturnix, Chapel Hill, 2010), p. 179.

G. Gbur and T.D. Visser, "The structure of partially coherent fields", in E. Wolf (Ed.), Prog. in Optics, vol. 55 (Elsevier, Amsterdam, 2010), p. 285.

Y. Gu and G. Gbur, "Scintillation of pseudo-Bessel correlated beams in atmospheric turbulence," J. Opt. Soc. Am. A 27 (2010), 2621-2629.

The concept of pseudo-Bessel correlated beams is introduced, and their scintillation properties o... more The concept of pseudo-Bessel correlated beams is introduced, and their scintillation properties on propagation through turbulence are investigated. By using the Rytov approximation, the scintillation index of pseudo-Bessel correlated beams is formulated in weak turbulence. The study of scintillation is extended into strong turbulence by numeric simulations. It is shown that by choosing an appropriate coherence parameter, pseudo-Bessel correlated beams have lower scintillation than comparable fully coherent beams in both weak and strong turbulence. In addition, the configuration of pseudo-Bessel correlated beams is modified by adding a horizontal beamlet; the scintillation properties of these modified beams are also discussed.

Y. Gu and G. Gbur, "Scintillation of Airy beam arrays in atmospheric turbulence," Opt. Lett. 35 (2010), 3456-3458.

We investigate the scintillation properties of Airy beam arrays in atmospheric turbulence. By uti... more We investigate the scintillation properties of Airy beam arrays in atmospheric turbulence. By utilizing the "selfbending" propagation property of Airy beams, the constituent beamlets propagate through relatively independent regions of turbulence but still largely overlap at the on-axis detector. Through numeric simulations, it is shown that the scintillation of an Airy beam array is significantly reduced and close to the theoretical minimum.

G. Gbur and S.M. Kim, "Magnetization effect in momentum conservation in partially coherent wavefields," Phys. Rev. A 82 (2010), 043807.

The law of momentum conservation and its applications for partially coherent electromagnetic fiel... more The law of momentum conservation and its applications for partially coherent electromagnetic fields has been recently studied with the emphasis on the electric polarization. In this work, we provide more complete expressions of the formalism by including magnetization. Even though polarization gives a dominant effect in momentum flow in electromagnetic wave systems in general, magnetization can also be important in optical metamaterials. Therefore, this more general formalism will be useful for some physical situations where magnetization can be nonnegligible.

Y. Gu and G. Gbur, " Measurement of atmospheric turbulence strength by vortex beam," Opt. Commun. 283 (2010), 1209-1212.

The behavior of spatial correlation singularities suggests a possible method for measuring atmosp... more The behavior of spatial correlation singularities suggests a possible method for measuring atmospheric turbulence strength with a vortex beam. The refractive index structure constant C 2 n can be obtained by measuring the radius of a ring dislocation of a vortex beam which has passed through atmospheric turbulence. An approximate analytic expression for the radius of a ring dislocation as a function of C 2 n has been derived, and its accuracy is verified by numerical examples.

C.H. Gan and G. Gbur, "Extraordinary optical transmission through multi-layered systems of corrugated metallic thin films," Opt. Exp. 17 (2009), 20553-20566.

Optical transmission through multi-layered systems of corrugated metallic thin films is investiga... more Optical transmission through multi-layered systems of corrugated metallic thin films is investigated by rigorous electromagnetic simulations based on an exact Green tensor method. Compared to a single metal slab of equivalent thickness and volume, it was found that the multi-layered system can significantly impede the field decay, often leading to transmission greater than that expected from the Fabry-Perot resonance-like behavior exhibited by subwavelength slits in a single slab. Extraordinary optical transmission is also observable for systems of layers whose combined thicknesses are much greater than the skin depth of the metal. Structures consisting of up to five layers with a net thickness of 500 nm for the metal films were considered in our study. These findings demonstrate that an appreciable fraction of the optical power that is incident on the thin metal films can be transmitted over distances greater than their skin depth using plasmonic resonances.

Y. Gu, O. Korotkova and G. Gbur, "Scintillation of nonuniformly polarized beams in atmospheric turbulence," Opt. Lett. 34 (2009), 2261-2263.

We demonstrate, through numerical simulations, that an appropriately chosen nonuniformly polarize... more 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.

S.M. Kim and G. Gbur, "Momentum conservation in partially coherent wave fields," Phys. Rev. A 79 (2009), 033844.

D. Moses, C.H. Gan, and G. Gbur, "Directional, nonpropagating, and polychromatic excitations in one-dimensional wave systems," Phys. Rev. E 79 (2009), 026606.

It has been demonstrated that, in a one-dimensional wave system, monochromatic waves may be gener... more It has been demonstrated that, in a one-dimensional wave system, monochromatic waves may be generated which are completely localized to the region of excitation or which propagate in only one direction. We further the discussion of such nonpropagating and directional excitations and demonstrate that they can be extended to excitations of an arbitrary finite number of frequencies. Two techniques for mathematically constructing these excitations are discussed. Furthermore, the relation between nonpropagating excitations and nonscattering scatterers is discussed. The results presented here may be useful in the development of devices for onedimensional and quasi-one-dimensional wave systems.

Y. Gu and G. Gbur, "Topological reactions of correlation vortices," Opt. Commun. 282 (2009), 709.

It is now well-appreciated that the correlation functions of partially coherent optical wavefield... more It is now well-appreciated that the correlation functions of partially coherent optical wavefields may possess phase singularities with properties similar to those that appear in monochromatic wavefields. Though much work has been done to investigate the generic properties of such correlation vortices, little effort has gone towards studying topological reactions associated with these vortices. In this paper we investigate three such reactions: (1) The break-up of a second-order optical vortex into first-order correlation vortices. (2) Creation and annihilation of correlation vortices. The behavior of correlation vortices on propagation. These results clearly demonstrate the relationship between optical vortices and correlation vortices, and suggest the possible use of correlation vortices as a probe of the statistical properties of a field or a medium.

C.H. Gan and G. Gbur, "Spatial coherence conversion with surface plasmons using a three-slit interferometer," Plasmonics 3 (2008), 111.

G. Gbur and G.A. Swartzlander, Jr., "Complete transverse representation of a correlation singularity of a partially coherent field," J. Opt. Soc. Am. B 25 (2008), 1422.

An understanding of correlation singularities is fundamentally important in imaging science. Unti... more An understanding of correlation singularities is fundamentally important in imaging science. Until now spatial coherence studies have examined a two-dimensional projection of the four-dimensional correlation function, finding so-called correlation vortices or correlation ring dislocations in a given transverse plane. Here we describe the properties and symmetries of the full four-dimensional correlation function. The general solution is found to be a hyperbola in two reduced dimensions. For perfect coherence this reduces to crossed straight lines, whereas in the incoherent limit it reduces to parallel lines. These results elucidate a number of previous experimental and theoretical observations regarding correlation singularities and suggest other behaviors of such singularities.

T. van Dijk, G. Gbur, and T. D. Visser, "Shaping the focal intensity distribution using spatial coherence," J. Opt. Soc. Am. A 25 (2008), 575.

The intensity and the state of coherence are examined in the focal region of a converging, partia... more The intensity and the state of coherence are examined in the focal region of a converging, partially coherent wave field. In particular, Bessel-correlated fields are studied in detail. It is found that it is possible to change the intensity distribution and even to produce a local minimum of intensity at the geometrical focus by altering the coherence length. It is also shown that, even though the original field is partially coherent, in the focal region there are pairs of points at which the field is fully correlated and pairs of points at which the field is completely incoherent. The relevance of this work to applications such as optical trapping and beam shaping is discussed.

S.M. Kim and G. Gbur, "Angular momentum conservation in partially coherent wavefields," Phys. Rev. A 86 (2012), 043814.

Angular momentum in electromagnetic wave systems is an important yet difficult subject to deal wi... more Angular momentum in electromagnetic wave systems is an important yet difficult subject to deal with, both classically and quantum mechanically. We investigate the angular momentum of partially coherent electromagnetic wave fields and establish the general formalism for angular momentum conservation, based on the Maxwell stress tensor for partially coherent sources and fields in the space-frequency domain. This formalism is applied to study the angular momentum properties of several classes of partially coherent electromagnetic beams possessing circulation.

Y. Gu and G. Gbur, "Reduction of turbulence-induced scintillation by nonuniformly polarized beam arrays," Opt. Lett. 37 (2012), 1553-1555.

We have explored a method to reduce turbulence-induced scintillation by using an incoherent beam ... more We have explored a method to reduce turbulence-induced scintillation by using an incoherent beam array composed of beamlets with nonuniform polarization. It is shown that significant scintillation reduction of such an incoherent beam array can be obtained by using nonuniformly polarized beamlets whose scintillation properties are optimized.

C. Rosenbury, G. Gbur and Y. Gu, "Phase singularities, correlation singularities, and conditions for complete destructive interference," J. Opt. Soc. Am. A 29 (2012), 410-416.

A previously derived condition for the complete destructive interference of partially coherent li... more A previously derived condition for the complete destructive interference of partially coherent light emerging from a trio of pinholes in an opaque screen is generalized to the case when the coherence properties of the field are asymmetric. It is shown by example that the interference condition is necessary, but not sufficient, and that the existence of complete destructive interference also depends on the intensity of light emerging from the pinholes and the system geometry; more general conditions for such interference are derived. The phase of the wave field exhibits both phase singularities and correlation singularities, and a number of nonintuitive situations in which complete destructive interference occurs are described and explained.

C.H. Gan, Y. Gu, T.D. Visser and G. Gbur, "Coherence converting plasmonic hole arrays," Plasmonics, 7 (2012), 313.

Simulations are presented that demonstrate that the global state of spatial coherence of an optic... more Simulations are presented that demonstrate that the global state of spatial coherence of an optical wavefield can be altered on transmission through an array of subwavelength-sized holes in a metal plate that supports surface plasmons. It is found that the state of coherence of the emergent field strongly depends on the separation between the holes and their scattering strength. Our findings suggest that subwavelength hole arrays on a metal film can be potentially employed as a plasmon-assisted coherence converting device, useful in modifying the directionality, spectrum, and polarization of the transmitted wave.

S. Sahin, G. Gbur and O. Korotkova, “Scattering of light from particles with semisoft boundaries,” Opt. Lett. 36 (2011), 3957-3959.

A three-dimensional multi-Gaussian function, being a finite sum of Gaussian functions, is adopted... more A three-dimensional multi-Gaussian function, being a finite sum of Gaussian functions, is adopted for modeling of a spherically symmetric scatterer with a semisoft boundary, i.e. such that has continuous and adjustable drop in the index of refraction. A Gaussian sphere and a hard sphere are the two limiting cases when the number of terms in multi-Gaussian distribution is one and infinity, respectively. The effect of the boundary's softness on the intensity distribution of the scattered wave is revealed. The generalization of the model to random scatterers with semisoft boundaries is also outlined.

X. Pang, G. Gbur and T.D. Visser, "The Gouy phase of Airy beams", Opt. Lett. 36 (2011), 2492-2494.

The phase behavior of Airy beams is studied, and their Gouy phase is defined. Analytic expression... more

G. Gbur, "Invisibility physics: Kerker's 'invisible bodies'", in B. Zivkovic, J. Goldman (Eds.), The Open Laboratory 2010 (Coturnix, Chapel Hill, 2010), p. 179.

G. Gbur and T.D. Visser, "The structure of partially coherent fields", in E. Wolf (Ed.), Prog. in Optics, vol. 55 (Elsevier, Amsterdam, 2010), p. 285.

Y. Gu and G. Gbur, "Scintillation of pseudo-Bessel correlated beams in atmospheric turbulence," J. Opt. Soc. Am. A 27 (2010), 2621-2629.

The concept of pseudo-Bessel correlated beams is introduced, and their scintillation properties o... more The concept of pseudo-Bessel correlated beams is introduced, and their scintillation properties on propagation through turbulence are investigated. By using the Rytov approximation, the scintillation index of pseudo-Bessel correlated beams is formulated in weak turbulence. The study of scintillation is extended into strong turbulence by numeric simulations. It is shown that by choosing an appropriate coherence parameter, pseudo-Bessel correlated beams have lower scintillation than comparable fully coherent beams in both weak and strong turbulence. In addition, the configuration of pseudo-Bessel correlated beams is modified by adding a horizontal beamlet; the scintillation properties of these modified beams are also discussed.

Y. Gu and G. Gbur, "Scintillation of Airy beam arrays in atmospheric turbulence," Opt. Lett. 35 (2010), 3456-3458.

We investigate the scintillation properties of Airy beam arrays in atmospheric turbulence. By uti... more We investigate the scintillation properties of Airy beam arrays in atmospheric turbulence. By utilizing the "selfbending" propagation property of Airy beams, the constituent beamlets propagate through relatively independent regions of turbulence but still largely overlap at the on-axis detector. Through numeric simulations, it is shown that the scintillation of an Airy beam array is significantly reduced and close to the theoretical minimum.

G. Gbur and S.M. Kim, "Magnetization effect in momentum conservation in partially coherent wavefields," Phys. Rev. A 82 (2010), 043807.

The law of momentum conservation and its applications for partially coherent electromagnetic fiel... more The law of momentum conservation and its applications for partially coherent electromagnetic fields has been recently studied with the emphasis on the electric polarization. In this work, we provide more complete expressions of the formalism by including magnetization. Even though polarization gives a dominant effect in momentum flow in electromagnetic wave systems in general, magnetization can also be important in optical metamaterials. Therefore, this more general formalism will be useful for some physical situations where magnetization can be nonnegligible.

Y. Gu and G. Gbur, " Measurement of atmospheric turbulence strength by vortex beam," Opt. Commun. 283 (2010), 1209-1212.

The behavior of spatial correlation singularities suggests a possible method for measuring atmosp... more The behavior of spatial correlation singularities suggests a possible method for measuring atmospheric turbulence strength with a vortex beam. The refractive index structure constant C 2 n can be obtained by measuring the radius of a ring dislocation of a vortex beam which has passed through atmospheric turbulence. An approximate analytic expression for the radius of a ring dislocation as a function of C 2 n has been derived, and its accuracy is verified by numerical examples.

C.H. Gan and G. Gbur, "Extraordinary optical transmission through multi-layered systems of corrugated metallic thin films," Opt. Exp. 17 (2009), 20553-20566.

Optical transmission through multi-layered systems of corrugated metallic thin films is investiga... more Optical transmission through multi-layered systems of corrugated metallic thin films is investigated by rigorous electromagnetic simulations based on an exact Green tensor method. Compared to a single metal slab of equivalent thickness and volume, it was found that the multi-layered system can significantly impede the field decay, often leading to transmission greater than that expected from the Fabry-Perot resonance-like behavior exhibited by subwavelength slits in a single slab. Extraordinary optical transmission is also observable for systems of layers whose combined thicknesses are much greater than the skin depth of the metal. Structures consisting of up to five layers with a net thickness of 500 nm for the metal films were considered in our study. These findings demonstrate that an appreciable fraction of the optical power that is incident on the thin metal films can be transmitted over distances greater than their skin depth using plasmonic resonances.

Y. Gu, O. Korotkova and G. Gbur, "Scintillation of nonuniformly polarized beams in atmospheric turbulence," Opt. Lett. 34 (2009), 2261-2263.

We demonstrate, through numerical simulations, that an appropriately chosen nonuniformly polarize... more 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.

S.M. Kim and G. Gbur, "Momentum conservation in partially coherent wave fields," Phys. Rev. A 79 (2009), 033844.

D. Moses, C.H. Gan, and G. Gbur, "Directional, nonpropagating, and polychromatic excitations in one-dimensional wave systems," Phys. Rev. E 79 (2009), 026606.

It has been demonstrated that, in a one-dimensional wave system, monochromatic waves may be gener... more It has been demonstrated that, in a one-dimensional wave system, monochromatic waves may be generated which are completely localized to the region of excitation or which propagate in only one direction. We further the discussion of such nonpropagating and directional excitations and demonstrate that they can be extended to excitations of an arbitrary finite number of frequencies. Two techniques for mathematically constructing these excitations are discussed. Furthermore, the relation between nonpropagating excitations and nonscattering scatterers is discussed. The results presented here may be useful in the development of devices for onedimensional and quasi-one-dimensional wave systems.

Y. Gu and G. Gbur, "Topological reactions of correlation vortices," Opt. Commun. 282 (2009), 709.

It is now well-appreciated that the correlation functions of partially coherent optical wavefield... more It is now well-appreciated that the correlation functions of partially coherent optical wavefields may possess phase singularities with properties similar to those that appear in monochromatic wavefields. Though much work has been done to investigate the generic properties of such correlation vortices, little effort has gone towards studying topological reactions associated with these vortices. In this paper we investigate three such reactions: (1) The break-up of a second-order optical vortex into first-order correlation vortices. (2) Creation and annihilation of correlation vortices. The behavior of correlation vortices on propagation. These results clearly demonstrate the relationship between optical vortices and correlation vortices, and suggest the possible use of correlation vortices as a probe of the statistical properties of a field or a medium.

C.H. Gan and G. Gbur, "Spatial coherence conversion with surface plasmons using a three-slit interferometer," Plasmonics 3 (2008), 111.

G. Gbur and G.A. Swartzlander, Jr., "Complete transverse representation of a correlation singularity of a partially coherent field," J. Opt. Soc. Am. B 25 (2008), 1422.

An understanding of correlation singularities is fundamentally important in imaging science. Unti... more An understanding of correlation singularities is fundamentally important in imaging science. Until now spatial coherence studies have examined a two-dimensional projection of the four-dimensional correlation function, finding so-called correlation vortices or correlation ring dislocations in a given transverse plane. Here we describe the properties and symmetries of the full four-dimensional correlation function. The general solution is found to be a hyperbola in two reduced dimensions. For perfect coherence this reduces to crossed straight lines, whereas in the incoherent limit it reduces to parallel lines. These results elucidate a number of previous experimental and theoretical observations regarding correlation singularities and suggest other behaviors of such singularities.

T. van Dijk, G. Gbur, and T. D. Visser, "Shaping the focal intensity distribution using spatial coherence," J. Opt. Soc. Am. A 25 (2008), 575.

The intensity and the state of coherence are examined in the focal region of a converging, partia... more The intensity and the state of coherence are examined in the focal region of a converging, partially coherent wave field. In particular, Bessel-correlated fields are studied in detail. It is found that it is possible to change the intensity distribution and even to produce a local minimum of intensity at the geometrical focus by altering the coherence length. It is also shown that, even though the original field is partially coherent, in the focal region there are pairs of points at which the field is fully correlated and pairs of points at which the field is completely incoherent. The relevance of this work to applications such as optical trapping and beam shaping is discussed.