Polarization state of the optical near-field

The polarization state of the optical electromagnetic field lying several nanometers above complex dielectric structures reveals the intricate light-matter interaction that occurs in this near-field zone. This information can only be extracted from an analysis of the polarization state of the detected light in the near-field. These polarization states can be calculated by different numerical methods well-suited to near--field optics. In this paper, we apply two different techniques (Localized Green Function Method and Differential Theory of Gratings) to separate each polarisation component associated with both electric and magnetic optical near-fields produced by nanometer sized objects. The analysis is carried out in two stages: in the first stage, we use a simple dipolar model to achieve insight into the physical origin of the near-field polarization state. In the second stage, we calculate accurate numerical field maps, simulating experimental near-field light detection, to supplement the data produced by analytical models. We conclude this study by demonstrating the role played by the near-field polarization in the formation of the local density of states.Comment: 9 pages, 11 figures, accepted for publication in Phys. Rev.

Polarization contrast in photon scanning tunnelling microscopy combined with atomic force microscopy

Photon scanning tunnelling microscopy combined with atomic force microscopy allows simultaneous acquisition and direct comparison of optical and topographical images, both with a lateral resolution of about 30 nm, far beyond the optical diffraction limit. The probe consists of a modified microfabricated silicon nitride tip mounted o­n a cantilever, commercially available for atomic force microscopy. The lateral resolution is further improved using 'supertips', by depositing a small needle o­n the silicon nitride tip. The combined microscopic technique is applied to thin films of indium tin oxide because of the small grain size and high surface flatness, providing high-resolution optical contrast and limited far-field scattering contribution. Polarization contrast is shown in experiments both changing the polarization of the incident and detected light. Approach curves, both measuring the optical signal and force interaction, show a difference in the optical coupling between p- and s-polarized incident light, p-Polarized light always provides optical contrast more correlated to topography than s-polarized light, both for incident and detected light, in agreement with theoretical models