Abstract: A method for controlling the speed of a laser pulse includes a step of applying a chirp to the pulse; and a step of focusing the pulse by means of an optical system having a longitudinal chromatic aberration; whereby an intensity peak of the pulse moves along a propagation axis following, over a finite propagation length, a speed profile dependent on the chirp and on the longitudinal chromatic aberration. The use of such a method for accelerating particles via laser, and a system for implementing such a method, are also provided.

Abstract: A method for characterizing a light beam includes separating the light beam by a separator optic into first and second sub-beams; propagating the first and second sub-beams over first and second optics, respectively, said first and second optics being respectively arranged so that the sub-beams on leaving the optics are separated by a time delay ?; recombining the sub-beams so that they spatially interfere and form a two-dimensional interference pattern; measuring the frequency spectrum of at least part of the interference pattern; calculating the Fourier transform in the time domain of at least one spatial point of the frequency spectrum, the Fourier transform in the time domain having a time central peak and first and second time side peaks; calculating the Fourier transform in the frequency domain for one of the side peaks; calculating the spectral amplitude AR(?) and the spatial-spectral phase ?R(x,y,?) for the Fourier transform in the frequency domain.

Abstract: A characterization method of a light beam includes separating the light beam into first and second sub-beams; propagating the first and second sub-beams over first and second optics respectively; the first sub-beam, which forms a reference beam, and the second sub-beam, which forms a characterized beam, being separated by a time delay ?; recombining the reference and characterized beams so that they spatially interfere and form a two-dimensional interference pattern; measuring the pattern to obtain a temporal interferogram; calculating the Fourier transform in the frequency domain of a spatial point of the interferogram, the Fourier transform having a frequency central peak and first and second frequency side peaks; calculating the Fourier transform in the frequency domain for the first or second time side peaks calculating the spectral amplitude and the spatial-spectral phase for the first or second frequency side peak of the Fourier transform in the frequency domain.

Abstract: Method of characterizing a light beam having the steps of: a) disposing the input ends of N >3 optical fibers on the path of the light beam, in such a way that a respective portion of the beam is coupled and propagates in each optical fiber and is emitted from its output end so as to form a respective secondary beam; b) introducing an angular spectral dispersion into the secondary beams by means of at least one dispersive element; c) propagating the dispersed secondary beams in such a way that they overlap to form an interferogram; d) acquiring an image of the interferogram; and e) extracting from the image of the interferogram an item of information relating to the spatial variation of the phase of the light beam at a plurality of wavelengths. Device for the implementation of such a method.

Abstract: Method of characterizing a light beam (FL) comprising the steps consisting in: a) disposing the input ends (EE1-EE11) of N>3 optical fibres (F01-F011) on the path of said light beam, in such a way that a respective portion of said beam is coupled and propagates in each optical fibre and is emitted from its output end (ES1-ES11) so as to form a respective secondary beam; b) introducing an angular spectral dispersion into said secondary beams by means of at least one dispersive element (RD); c) propagating the dispersed secondary beams in such a way that they overlap to form an interferogram; d) acquiring an image of said interferogram; and e) extracting from said image of said interferogram an item of information relating to the spatial variation of the phase of said light beam at a plurality of wavelengths. Device for the implementation of such a method.

Abstract: To generate radiation or particles by interaction between a laser beam and a target, the selected target is a free flow (5) in a vacuum enclosure (40) of a powder made up of solid grains of size from 10 ?m to 1 mm and the laser beam (9), which is an intense pulsed laser beam, is focused onto the powder flow (5) that is driven by gravity only, to create an interaction area (8) generating the radiation or the particles in the vacuum enclosure (40), in which the internal pressure is less than 1000 Pa.