Pseudomodulation transfer function in reflection scanning near-field optical microscopy

In near-field optical microscopy, the resolution is strongly related to the experimental conditions of illumination and to the distance between the tip and the sample. Therefore, an intrinsic modulation transfer function is generally meaningless in near-field microscopes. In this paper, we show that experimental microscopes can be characterized by a linear transfer, according to a few experimental conditions, we consequently establish the existence of a pseudo modulation transfer function (PMTF). We calculate it, in the R-SNOM (reflection scanning near-field optical microscope) case. The PMTF is an efficient tool for determining the SNOM capabilities, if the tip to sample distance is large enough, without resorting to well-known test samples. This characterization could provide information on the resolving power of the microscope, working on a wide scanning zone, to choose an interesting sample area. (C) 1998 Elsevier Science B.V. All rights reserved.