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

Abstract

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.

Coherence Stokes Parameters in the Description of Electromagnetic Coherence

“…Insight into the connection between polarization and coherence is provided by the coherence or two-point Stokes parameters, originally introduced by Ellis and Dogariu [6] and later studied by others [7,8]. These parameters are the two-point versions of the customary polarization (one-point) Stokes parameters and they have been recently successfully used, e.g., in spatial [9][10][11][12][13] and temporal [14,15] interferometry, analysis of field propagation [16], nanoscattering [17,18], as well as with quantized light fields [19].…”

Spatial coherence of light measured by nanoscattering

“…Quite recently it was predicted that using two nanoparticle probes and observing the visibility of the intensity fringes that their scattered fields produce in the far zone yields the degree of spatial coherence of the light at the particle sites [10]. A single nanoprobe acts as a local scatterer transferring information on the field at the probe, including its statistical characteristics [11], into the far field.…”

“…In addition, the far fields generated in probe and pinhole techniques are produced by dipole scattering and aperture diffraction, respectively. As shown in [10], the fringe pattern in the former case is equipped with a specific geometric factor. We also note that the use of subwavelength nanoapertures would lead to added complexity, as their far fields depend highly on the material and thickness of the aperture screen as well as on the size of the holes [12].…”

“…In this work, we demonstrate the first measurement of the spatial coherence of optical beams with nanoprobes. We consider fully polarized light (allowing scalar treatment), but the technique can be extended to partially polarized beams as well [10]. The probes are gold cube-shaped nanoparticles deposited on a silicon substrate.…”

“…The beam power after the polarizer was approximately 2.65 mW for both sources. While we consider fully polarized light in this work, the technique can readily be extended to beams of arbitrary states of partial polarization as well [10].…”