320 research outputs found
Degree of polarization in near fields of thermal sources: effects of surface waves
We introduce the concept of degree of polarization for electromagnetic near fields. The approach is based on the generalized Stokes parameters that appear as expansion coefficients of the 3Ă—3 coherence matrix in terms of the Gell-Mann matrices. The formalism is applied to optical near fields of thermally fluctuating half-space sources with particular interest in fields that are strongly polarized owing to resonant surface plasmons or phonons. This novel method is particularly useful when assessing the full vectorial characteristics of random evanescent fields, e.g., for near-field spectroscopy and polarization microscopy.Peer reviewe
Decomposition of the point-dipole field into homogeneous and evanescent parts
In near-field optics the resolution and sensitivity of measurements depend on the abundance of evanescent waves in relation to propagating waves. The electromagnetic field propagator is related to the scalar spherical wave, for which the Weyl expansion is a half-space representation containing both evanescent and homogeneous plane waves. Making use of these results, we decompose the dyadic free-space Green function into its evanescent and homogeneous parts and show that some approaches put forward in the literature are inconsistent with this formulation. We express the results in a form that is suitable for numerical computation and illustrate the field decomposition for a point dipole in some typical cases.Peer reviewe
Image quality in double- and triple-intensity ghost imaging with classical partially polarized light
Classical ghost imaging is a correlation-imaging technique in which the image
of the object is found through intensity correlations of light. We analyze
three different quality parameters, namely the visibility, the signal-to-noise
ratio (SNR), and the contrast-to-noise ratio (CNR), to assess the performance
of double- and triple-intensity correlation-imaging setups. The source is a
random partially polarized beam of light obeying Gaussian statistics and the
image quality is evaluated as a function of the degree of polarization (DoP).
We show that the visibility improves when the DoP and the order of imaging
increase, while the SNR behaves oppositely. The CNR is for the most part
independent of DoP and the imaging order. The results are important for the
development of new imaging devices using partially polarized light.Comment: Added 2 references, corrected a few typos and revised text slightly.
Results unchange
Cross-spectral purity of the Stokes parameters in random nonstationary electromagnetic beams
We consider cross-spectral purity in random nonstationary electromagnetic
beams in terms of the Stokes parameters representing the spectral density and
the spectral polarization state. We show that a Stokes parameter being
cross-spectrally pure is consistent with the property that the corresponding
normalized time-integrated coherence (two-point) Stokes parameter satisfies a
certain reduction formula. The current analysis differs from the previous works
on cross-spectral purity of nonstationary light beams such that the purity
condition is in line with Mandel's original definition. In addition, in
contrast to earlier works concerning the cross-spectral purity of the
polarization-state Stokes parameters, intensity-normalized coherence Stokes
parameters are applied. It is consequently found that in addition to separate
spatial and temporal coherence factors the reduction formula contains a third
factor that depends exclusively on the polarization properties. We further show
that cross-spectral purity implies a specific structure for the electromagnetic
spectral spatial correlations. The results of this work constitute foundational
advances in the interference of random nonstationary vectorial light.Comment: 5 pages, 1 figur
Polarimetric nonregularity of evanescent waves
Three-dimensional polarization states of random light can be classified into regular and nonregular according to the structure of the related 3 Ă— 3 polarization matrix. Here we show that any purely evanescent wave excited in total internal reflection of a partially polarized plane-wave field is always in a nonregular polarization state. The degree of nonregularity of such evanescent waves is also studied in terms of a recently advanced measure. Nonregular evanescent waves uncover new aspects of the polarimetric structure and dimensional character of electromagnetic near fields, with potential applications in nanoscale surface optics
Polarization time and length for random optical beams
We investigate the dynamics of the instantaneous polarization state of stationary, partially polarized random electromagnetic beamlike fields. An intensity-normalized correlation function of the instantaneous Poincaré vector is introduced for the characterization of the time evolution of the polarization state. This polarization correlation function enables us to define a polarization time and a polarization length over which the polarization state remains substantially unchanged. In the case of Gaussian statistics, the polarization correlation function is shown to assume a simple form in terms of the parameters employed to characterize partial coherence and partial polarization of electromagnetic fields. The formalism is demonstrated for a partially polarized, temporally Gaussian-correlated beam, and black-body radiation. The results are expected to find a range of applications in investigations of phenomena where polarization fluctuations of light play an important role.Peer reviewe
Universality of electromagnetic-field correlations within homogeneous and isotropic sources
We investigate the structure of second-order correlations in electromagnetic fields produced by statistically stationary, homogeneous, and isotropic current distributions. We show that the coherence properties of such fields within a low-loss or nondissipative medium do not depend on the source characteristics, but are solely determined by the propagation properties, and that the degree of coherence of the field is given by the sinc law. Our analysis reproduces the known results for blackbody fields, but it applies to a wider class of sources, not necessarily in thermal equilibrium. We discuss the physics behind the universal behavior of the correlations by comparing the results with those obtained by an electromagnetic plane-wave model.Peer reviewe
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