An interferometric method is used to enhance the weak scattered signal in apertureless near-field scanning infrared microscopy. The method involves introducing a homodyning reference field, and amplifies the desired signal field by the magnitude of the reference field. This method markedly improves the signal-to-noise ratio of the detected signal, over the nonhomodyned experiment. A model for the dependence of the near-field signal, as a function of the normal distance of the tip from the surface, is discussed. Application of a model in which the tip is represented by two spherical scatterers, one large and one small, indicates the electromagnetic field enhancement is 90-fold greater at the sharp apex of the metallic probe tip.
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Stebounova et al. (2003) studied this question.
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