Device for analyzing a polyphase mixture (2) via a light beam (3) backscattered by said mixture, comprising: a vertical cell (1) capable of containing the polyphase mixture; means (4) for emitting a light beam (5) in the direction of the cell, in such a way that the light beam lies in a vertical plane (PV) covering at least the height (hc) of the cell containing the polyphase mixture (2); means (6) for receiving a light beam (3) backscattered by the polyphase mixture, covering the height of the backscattered light beam (3), extending over the height (hc) of the cell containing the polyphase mixture (2); optical conjugation means (17) placed between the cell (1) and the means (6) for receiving the backscattered beam (3), the receiving means (6) comprising a matrix centre (20) forming a surface for receiving the backscattered beam, lying in vertical and horizontal directions; and means (7) for analyzing the backscattered beam received by the matrix sensor, the light beam (5) emitted in the direction of the cell, adopting, at its interface (9) between the internal surface (10) of the wall (18) of the cell (1) and the polyphase mixture (2), the form of a vertical line (16) the width of which is shorter, preferably very much shorter, than the free transport path (1*) of the polyphase mixture (2).