Abstract: A device for analyzing the wave surface of a light beam has an entry lens which defines a reference plane, optically conjugate with the plane in which the wave surface of the light beam is analysed. A bidimensional meshed lattice is placed in this reference plane, perpendicularly to the beam. The different sub-beams, due to the different orders of diffraction, are focused jointly by a first lens, in an intermediate focal plane, in the vicinity of which a mask selects, from the sub-beams, those which relate to at least three distinct orders of diffraction. A second lens takes the selected sub-beams to a nil-sensitivity plane, conjugate with the plane of the lattice. An interference image is observed in a working plane, situated at a chosen distance from the nil-sensitivity plane. The device can be characterized as an improved achromatic optical interferometer, of the trilateral shift type.