Connection of electromagnetic degrees of coherence in space-time and space-frequency domains.

We study the relationship between the electromagnetic degrees of coherence of stationary random fields in the space-time and space-frequency domains. In contrast to a known result on scalar fields, it appears that, due to the structure of the electromagnetic degree of coherence, no general closed-form relationship exists for the electromagnetic degrees in the two domains. However, relations that illustrate the similarities and differences between the two quantities can be established by specific considerations covering quasi-monochromatic and broadband situations of electromagnetic Gaussian Schell-model beams and blackbody radiation.

Detection of partial polarization of light beams with dipolar nanocubes.

We confirm experimentally that the degree and state of polarization of a random, partially polarized electromagnetic beam can be obtained by probing the field with a nanoscatterer. We use a gold nanocube on silicon substrate as a local scatterer and detect the polarization characteristics of the scattered far field, which enables us to deduce the state of partial polarization of the field at the nanoprobe site. In contrast to previous beam characterization methods where spatial resolution is limited by the pixel size of the detector, the accuracy of the current technique is specified by the particle size. Our work is the first step towards polarization-state detection of random optical near fields for which the use of nanoprobes is required.

Detection of electromagnetic degree of coherence with nanoscatterers: comparison with Young's interferometer.

We show theoretically that the (spectral) electromagnetic degree of spatial coherence of a random, stationary light beam can be measured by using two dipolar nanoscatterers instead of aperture diffraction as in traditional Young's interferometer. The method is based on considering individually the correlation functions associated with the six polarization states that make up the coherence (two-point) Stokes parameters and observing separately the visibilities and the locations of the intensity fringes created by the interfering dipole fields, leading to a complete characterization of the beam's second-order spatial coherence. The novel technique, although introduced in this work for beams, paves the way toward the detection of spatial coherence in nonparaxial optical near-fields for which the use of nanoscatterers is necessary.

Partial polarization of optical beams and near fields probed with a nanoscatterer.

We consider theoretically the detection of the spectral polarization characteristics of random, partially polarized optical beams and near fields by probing them with a dipolar nanoparticle. We show that measuring the polarization state of the scattered far field with a conventional waveplate-polarizer setup, possibly in several directions, results in the full 3×3 polarization matrix at the probe site. This allows us to deduce the distributions of the degree of polarization of the field and the Stokes parameters of the polarized part of the field with a resolution limited by the probe size. Regarding random near fields we show that, in analogy with a known result on beam fields, a degree of polarization of three-component light fields put forward in recent literature can in some cases be interpreted as a ratio of the intensity in the polarized part of the light to that of the total field. We demonstrate the technique by considering the probing of a Gaussian-Schell model beam and a thermally excited near field. The method extends the current scanning-probe techniques to the detection of partial polarization of random light fields and can find applications in nanophotonics and polarization optics.