The role of scanning mode in near-field optical microscopy

In this paper, a comparison between the three different scanning modes of current use in Scanning Tunneling Optical Microscopy (STOM), i.e. constant height, constant distance and constant intensity modes, is discussed from a realistic theoretical scheme. Starting from a three-dimensional test object, we compare the numerical images issued from these three different acquisition procedures. The numerical approach is based on a fully vectorial three-dimensional description in which the sample is characterized by a unique generalized propagator independent of the illumination mode. The discussion of the numerical results is given for different values of the incident polarization. (C) 1997 Elsevier Science B.V.