Numerical comparison between constant-height and constant-intensity images in scanning near field optical microscopy

Abstract

Within a microscopic theory, we present numerical simulations of scanning near field optical microscopy for constant-height, constant-intensity and near-field (under shear-force distance regulation) imaging methods. Our primary interest is to compare the constant-height and constant-intensity images. We clearly demonstrate that the two images are different particularly for near field. Both images may resolve subwavelength features, but constant-height images are more or less associated with far field diffractions. Finally, we use two simple examples to show the following. For the far field components whose distance dependence from the surface is about 1/ z, the two images are somewhat similar, while, for near field components whose distance dependence is as fast as 1/ z 3, the two images are quite different. In other words, the more near field the bigger the difference.