Prof. Dr. Alain Dereux
Laboratoire de Physique, Université de Bourgogne, Dijon

This contribution presents key results to understand correctly near-field optical microscope images in order to bring to the fore potential applications dealing with subwavelength optical devices and surface chemical physics. Two types of near-field optical microscopes can be distinguished. In illumination mode near-field optical microscopes, the light is incident through the local probe which scans the sample surface. In collection mode near-field optical microscopes, the light is incident through the substrate so that the tip is used for local detection purpose only. In order to find a definitive issue to the controversial question of defining the resolution of a near-field optical microscope, we propose a practical point of view defining a subwavelength detection process. On the basis of simple physical arguments, this point of view expects that the solutions of Maxwell equations should agree with images obtained by collection mode near-field microscopes, while the electromagnetic local density of states (LDOS) should be considered to provide an interpretation of illumination mode near-field microscopes images. We report near-field microscope images which support this practical point of view both in collection and illumination modes.