Abstract: The present invention relates to a device (1) for characterizing an interface of a structure (6), said structure (6) comprising a solid first material and a second material, the materials being separated by said interface. The device (1) comprises: means (2) for generating a first mechanical wave; means (2) for forming Brillouin oscillations; means (10) for detecting time variation of the Brillouin oscillations; means (12) for responding to the time variation of the Brillouin oscillations to identify reflection of said first mechanical wave by said interface or transmission through said interface of a second mechanical wave interfering with the first mechanical wave; and means (13) for determining the variation in amplitude of the Brillouin oscillations before and after reflection or transmission by said interface. The invention also relates to a corresponding method of characterization.