Speckle Pattern in the Near Field

International audienceAnalysis of the speckle structure of a random field is a well-known topic. With the development of near-field microscopy, the subject has been revisited in the last ten years. This paper addresses the structure of a random field in close proximity to an interface. First, we give a general overview of the differences between the structure of the field in the near field and in the far field. We emphasize the role of the evanescent waves in the near field. The second part of the paper reviews recent studies on field correlations in the near field for two cases: random thermal fields and light multiply scattered. The third part of the paper is devoted to the analysis of the speckle pattern above an interface in the single scattering regime. It is shown that in that case, the speckle pattern is nonuniversal and strongly related to the statistical properties of the surface. It is known that near-field images strongly depend on the specific properties of each tip. It cannot be assumed in general that the signal delivered by a near-field scanning microscope delivers a signal proportional to the square of the local electric field. In the last part of the paper, we derive from the reciprocity theorem a general form of the signal. In particular, we emphasize the role of polarization and the influence of the tip on the spectral response