Device which measures the mutual coherence function of a laser beam

A device for measuring the mutual coherence function of a laser beam, said device including:

• a plane screen constituted by a material capable of blocking the energy of the laser beam, said screen being disposed perpendicular to the axis of the beam and having 2n+1 openings so as to pass 2n+1 pencils of laser light taken from the beam, said openings being disposed along a straight line of said screen and including a central opening, a first group of n openings situated to one side of the central opening and a second group of n openings disposed on the other side of the central opening symmetrically in relation to the central opening, n being an integer;
• a partially reflecting optical plate disposed to pass a fraction of the energy of each pencil of light therethrough and to reflect the other fraction of the energy of each pencil of light at 90 degrees parallel to said straight line;
• a rectangular dihedron having opposed inner reflecting surfaces, said surfaces comprising a first surface and a second surface respectively parallel and perpendicular to the plane of the optical plate with the edge of the dihedron being perpendicular to said straight line, the reflecting surfaces of the dihedron being disposed to receive the pencils of light which are reflected by the optical plate, the pencil of light which emerges from the central opening reaching the edge of the dihedron and being returned on its own path so that part of its energy passes through the plate to form a reference pencil of light;
• a plane mirror disposed to return on its own path said fraction of energy of the pencils of light which has passed through the optical plate;
• a modulator for modulating the phase of said fraction of energy of the pencils of light, said modulator being situated on the path of the pencils of light after passing through the optical plate;
• n+1 photoelectric receivers including a reference receiver disposed to receive the reference pencil of light and n measuring receivers disposed to receive respectively the n pencils of light which emerge from the openings of the first group after they have been successively reflected on the optical plate, said first surface and said second surface of the dihedron and after they have subsequently passed through the optical plate with the n pencils of light being respectively superposed on the n pencils of light which emerge from the openings of the second group having passed through the optical plate then having been reflected successively on the plane mirror and on the optical plate;
• and
• a processing circuit for determining over a predetermined time the amplitude of the signals delivered by each of the n measuring receivers and over said predetermined time the average values of the phase difference between the signals delivered by each of the n measuring receivers and the signal delivered by the reference receiver, whereby these average amplitude values and average phase values are representative of the amplitude and of the phase of the mutual coherence function relating to the points of the cross-section of the laser beam which correspond to the openings of the screen.