PSEUDOMODULATION TRANSFER-FUNCTION IN REFLECTION SCANNING NEAR-FIELD OPTICAL MICROSCOPY

In near-field optical microscopy, the resolution is strongly related t o the experimental conditions of illumination and to the distance betw een the tip and the sample. Therefore, an intrinsic modulation transfe r 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 cons equently establish the existence of a pseudo modulation transfer funct ion (PMTF). We calculate it, in the R-SNOM (reflection scanning near-f ield optical microscope) case. The PMTF is an efficient tool for deter mining the SNOM capabilities, if the tip to sample distance is large e nough, without resorting to well-known test samples. This characteriza tion could provide information on the resolving power of the microscop e, working on a wide scanning zone, to choose an interesting sample ar ea. (C) 1998 Elsevier Science B.V. All rights reserved.