Near-field to far-field characterization of speckle patterns generated by disordered nanomaterials

TL;DR

This paper investigates how optical speckle patterns evolve from near-field to far-field regimes in disordered nanomaterials, revealing the link between near-field speckles and internal structure using SNOM.

Contribution

It introduces a method to characterize speckle patterns across different regimes with sub-wavelength resolution, connecting near-field speckles to internal medium structure.

Findings

Speckle patterns vary non-universally at sub-wavelength distances.

Near-field speckles are linked to the internal structure of disordered media.

The study demonstrates continuous transition from near-field to far-field speckle behavior.

Abstract

We study the intensity spatial correlation function of optical speckle patterns above a disordered dielectric medium in the multiple scattering regime. The intensity distributions are recorded by scanning near-field optical microscopy (SNOM) with sub-wavelength spatial resolution at variable distances from the surface in a range which spans continuously from the near-field (distance $ \ll \lambda $) to the far-field regime (distance $\gg \lambda $). The non-universal behavior at sub-wavelength distances reveals the connection between the near-field speckle pattern and the internal structure of the medium.