Abstract: A device for guiding a civil engineering/earthmoving machine using laser beams having a laser emitter and two laser receivers each mounted on a displacement unit mobile with two degrees of freedom. Two receiver position sensors are associated with each unit to measure its position with reference to two degrees of freedom and to generate signals representative of this position. A machine position sensor measures the position of the machine with reference to a fifth degree of freedom and generates a signal representing this position. A computer responsive to these signals stores the geometrical features of the surface over which the machine is guided and controls each receiver in two dimensions to maintain it centered on the beam from the laser emitter. The computer also generates in real time command instructions applied to actuators controlling the machine, on the basis of these geometrical features.

Abstract: The optical filter device comprises a stack of thin layers exhibiting a sequences h and g which defines a fractal organization. This device makes it possible to obtain spectrum lines which are extremely fine and very well resolved.

Abstract: The alignment apparatus is intended for repairing welds using infrared radiation and a weldhead (30) inside a heat exchanger tube (14) in the water box (20) of a steam generator associated with a nuclear reactor. A power beam (PE, PL, PS) is transported to the axis (24) of a tube (14) to be treated via two motor-driven light deflectors referred to as an "emitter" (11) fixed adjacent to an access hole into the water box, and as a "receiver" (12) carried by a "carrier" (22) at the entrance to the tube to be treated. The power beam is surrounded coaxially by a visible beam (AE, AL, AS) which is used for establishing and maintaining an optical connection between the emitter and the receiver by means of retroreflectors (15) and an autocollimation mirror (17) carried by the receiver (12) and by detectors (16, 18) carried by the emitter (11).