Twisted vortex Gaussian Schell-model beams.

We introduce a new class of partially coherent vortex beams in which the angular momentum of the beam is provided from two different sources: the underlying vortex of the random beam and the "twist" given to the ensemble of beams. The statistical and propagation properties of such beams are investigated, and their orbital angular momentum properties are analyzed. The combination of distinct orbital angular momentum sources allows unusual behaviors that were previously unobserved.

Partially coherent vortex beams of arbitrary order.

We derive analytic solutions for an infinite set of partially coherent vortex beams (PCVBs) of any azimuthal order and for any propagation distance. The correlation singularities of the beams and their orbital angular momentum are investigated. This detailed study of PCVBs opens the possibility of using such beams for remote sensing and free-space optical communications.

Complete representation of a correlation singularity in a partially coherent beam.

An understanding of phase singularities of correlation functions is important in optical coherence theory and imaging science, but to date such singularities have only been theoretically studied in a single transverse plane, at most. In this Letter we evaluate the complete structure of a correlation singularity of a partially coherent Laguerre-Gauss beam, describing it in both the transverse and the propagation directions. These results agree with previously found solutions, and introduce new aspects of correlation singularities.

Enhancement of spatial coherence by surface plasmons.

We report on a method to generate a stationary interference pattern from two independent optical sources, each illuminating a single slit in Young's interference experiment. The pattern arises as a result of the action of surface plasmons traveling between subwavelength slits milled in a metal film. The visibility of the interference pattern can be manipulated by tuning the wavelength of one of the optical sources.

Plasmon-assisted two-slit transmission: Young's experiment revisited.

We present an experimental and theoretical study of the optical transmission of a thin metal screen perforated by two subwavelength slits, separated by many optical wavelengths. The total intensity of the far-field double-slit pattern is shown to be reduced or enhanced as a function of the wavelength of the incident light beam. This modulation is attributed to an interference phenomenon at each of the slits, instead of at the detector. The interference arises as a consequence of the excitation of surface plasmons propagating from one slit to the other.

Anomalous behavior of spectra near phase singularities of focused waves.

It is shown that remarkable spectral changes take place in the neighborhood of phase singularities near the focus of a converging, spatially fully coherent polychromatic wave diffracted at an aperture. In particular, when the spectrum of the wave in the aperture consists of a single line with a narrow Gaussian profile, the spectrum near a phase singularity (i.e., near points of zero intensity of some particular spectral component) changes drastically along a closed loop around the singularity. The spectrum is redshifted at some points, blueshifted at others, and is split into two lines elsewhere.

Relation between computed tomography and diffraction tomography.

The relationship between computed tomography (CAT) and diffraction tomography (DT) is investigated. A simple condition with a clear physical meaning is derived for the applicability of CAT. Corrections due to scattering are incorporated into CAT, and it is shown that the effect of scattering may be characterized by a two-dimensional fractional Fourier transform. The implications of these results for the three-dimensional imaging of weakly scattering objects are also discussed.

Phase conjugation with random fields and with deterministic and random scatterers.

The theory of distortion correction by phase conjugation, developed since the discovery of this phenomenon many years ago, applies to situations when the field that is conjugated is monochromatic and the medium with which it interacts is deterministic. In this Letter a generalization of the theory is presented that applies to phase conjugation of partially coherent waves interacting with either deterministic or random weakly scattering nonabsorbing media.

Sources of arbitrary states of coherence that generate completely coherent fields outside the source.

A new theorem concerning nonradiating stochastic sources is derived. The theorem is used to describe sources that can have a variety of different states of coherence and yet each of them generating a field that is completely spatially coherent outside the source domain. The bearing of this result on a basic unsolved problem is spectroscopy of partially coherent sources is noted.