Abstract: An optical device for focusing a light beam. The device includes a Fourier diffractive element that can separate an incident beam into n beams along n directions which are symmetric about an optical axis. The device also includes a diffractive element including n Fresnel lenses capable of refocusing the n beams onto the optical axis. The device may be used with lasers and laser cutting devices.

Abstract: It includes a measuring space (8) comprising a constrained passage (15) for the fluid, a monochromatic light source (31) delivering a beam (F1) to optical elements (6, 32, 34) including a first diffractive optical element (32) having a diffractive network (38) predetermined as a function, on the one hand, of the characteristics of the source and, on the other hand, of chosen geometrical and spectral characteristics for the illumination of the constrained passage, and suitable for inducing fluorescence of at least part of the fluid, and first (19-20), second (34-36) and third (40) optoelectronic elements intended to collect, respectively, a transmitted beam, fluorescence and a diffracted beam, and suitable for delivering to an analysis unit (24) signals relating to the contents of the beams.