An optical detection device comprises a light source (9) that emits a light beam with an electromagnetic field, means suitable for splitting the beam (91) into a first beam defining a first, control path (80), and a second beam defining a second, sample path (70), a modulation system (78) which shifts the frequency of the electromagnetic fields of the two beams, a beam coupler (92) suitable for combining the beams, an optical detection system (50) suitable for detecting the signal resulting from the interference between the beams coupled by the coupler, the sample being placed in the sample path (70), the optical detection system (50) comprising an optical detector (5) and a device suitable for measuring the amplitude and phase of the signal (6), an opaque screen (2) comprising an optical aperture (20) being placed on a sample zone near the sample in the sample path (70).