Abstract: The active ring gyrometer comprises a path closed by mirrors (11,12,13) forming a resonant cavity (10) in which is placed a cell (20) containing an optically non-linear medium which permits by a four wave mixture the coherent auto-oscillation of two conjugated counter-rotative waves. The gyrometer further includes two pumping laser beams (31, 32), an optical device (40) for irradiating the medium of the cell, an optical system (50) for causing these two waves to interfere, and a detector (60). The optically non-linear medium and the intensity modulators (70) of the pumping beams permit the production of an optical "bias" which eliminates the blind zone in which the gyrometer is unsuitable for measuring relatively low rates of rotation.

Abstract: A process for producing a fluidtight seal between a body of a vitroceramic material and a metal element intended to be part of the construction of a gas laser and in particular a laser gyrometer includes interposing between the surfaces of the body of vitroceramic material and the metal element to be sealed a joining member of a metal capable of diffusing into the vitroceramic material, and subjecting the assembly thus formed to a thermo-compression operation so as to result in a superficial diffusion of the material of the joining member into the facing surfaces of the body of vitroceramic material and the metal element.

Abstract: A filtering element for a beam of coherent light, comprising a diffraction grating placed in the path of the beam and disposed with respect to the direction of the beam in such manner that the angle of incidence of the beam is at least equal to 80.degree. and different from the angle of diffraction. At least one additional optical element is placed in the path of a component of the beam diffracted by said grating for returning to the grating a part of the light of said component.

Abstract: The mirror comprises a multilayer structure, at least one of the component layers of which is made from a piezoelectric material, and electrodes for applying voltage to the multilayer structure. A free face of the multilayer structure carries the reflecting surface of the mirror. At least one of the outer faces of the mirror comprises at least one zone of curvature which is non-zero in the non-excited state of the multilayer structure.

Abstract: The optical device comprises at least two optical elements (M.sub.1, M.sub.2 ; L.sub.1, L.sub.2, L.sub.3 ; L.sub.1, M.sub.2) which are of variable focal length and include multilayer structures, at least one source of voltage (47) for the multilayer structures and electronic control means for controlling the voltage applied to the respective multilayer structures of the optical elements of variable focal length as a function of the magnification desired for the optical device.

Abstract: The optical element comprises a first bimorph structure, at least one of the components of which is made from piezoelectric material and supply electrodes for the bimorph structure. The element further comprises at least one reinforcing piezoelectric bimorph structure provided with supply electrodes. The latter are respectively connected to the electrodes of the first bimorph structure. An element of the reinforcing bimorph structure is placed against a corresponding element of the first bimorph structure and fixed thereto by a layer of an elastic material. The latter has a tensile strength which is low relative to that of the elements constituting the bimorph structures of piezoelectric material.

Abstract: It comprises a container made at least partly from a transparent material and filled with an index adapting medium. At least one of the walls of the container through which the optical axis of the system extends comprises a piezoelectric multilayer structure for modifying the curvature of the wall in accordance with the voltage applied to the multilayer structure.

Abstract: The laser oscillator comprises an optical amplifying medium and a diaphragm disposed between two mirrors defining a cavity. The diaphragm is placed between the amplifying medium and the mirror having a high coefficient of reflection. A polarizer is placed between the diaphragm and the amplifying medium. A device for rotating the polarization of the output beam of the oscillator and for transforming and returning this beam by reflection to the amplifying medium and the polarizer is provided so that, when the beam again reaches the amplifying medium, it has a section roughly equal to the section of the amplifying medium.

Abstract: A method for eliminating small-scale, spatial intensity fluctuations in laser beams is disclosed comprising the steps of placing in the path of the laser beam at least one nonlinear filtering element constituted by a fluid medium, having an index of refraction increasing with the intensity of light passing through the fluid medium and focusing only the laser's small-scale, spatial intensity fluctuations above a predetermined power threshold at a focal point within the fluid medium whereby the energy contained in these fluctuations is dissipated. Alternatively, the nonlinear filter element can be constituted by a fluid medium wherein high-frequency sound waves propagate with low attenuation wherein only the small-scale, spatial intensity fluctuations above a stimulated Brillouin power threshold are back-reflected whereby the energy contained in those fluctuations is eliminated.