Polarization dependent near-field speckle of random gold films

The near-field speckle of random gold nanostructures is experimentally and theoretically investigated. The topography and the intensity distribution, under polarized illumination, are obtained with an aperture scanning near-field optical microscope. The sharpness of the experimental images entitles us to perform a fine statistical analysis based on the autocorrelation function (ACF). The intensity ACF clearly exhibits an anisotropic behavior and subwavelength oscillations, depending on the incident polarization. A comparison with a numerical simulation exhibits the influence of the surface topography on the anisotropic near-field speckle.