Near field optical microscopy using a metallic vibrating tip

We present here an alternative experimental approach to achieve a local selection of a field distribution smaller than the wavelength. The sample surface is irradiated by a strongly converging beam issued from a microscope objective. A tungsten tip is used to perturb locally and periodically the electromagnetic field in the diffraction limited spot. The vibration amplitude is kept at a constant value when scanning the sample. We expect this to discard the topographical response and to retain mainly the optical response of the sample. We can use our microscope as an ordinary scanning metallographic one by monitoring the DC level of the reflected light and compare this signal with the AC signal induced by the tip oscillation on the same detector. Preliminary results obtained show a clear improvement of the resolution compared to the diffraction limited one.