SNOM device using heterodyne detection

An optical detection device includes a light source emitting a light beam whose electromagnetic field, a means adapted to divide the beam into a first beam defining a first reference pathway and a second beam defining a second sample pathway, a modulation system frequency-shifting the electromagnetic fields of the two beams, a beam coupler adapted to collect the beams, an optical detection system adapted to detect the signal arising from the interference between the beams and coupled via the coupler, the sample being placed in the sample pathway, the optical detection system comprising an optical detector and a device adapted to measure the amplitude and the phase of the signal, an opaque screen comprising an optical aperture is placed at the level of a zone of a sample, in proximity to the sample, in the sample pathway.