Device for forming laser pulses intended to convert a laser pulse from an input pulsed laser beam into a train of individual output pulses exhibiting temporal intensity modulation, this device comprising: - an input for allowing an input pulsed laser beam to enter; - a spatial phase modulator, arranged on the path of said input pulsed laser beam to be illuminated thereby, and consisting of pixels arranged on a surface of the modulator, each programmable separately to introduce a phase shift of between 0 and 2π, organised on the surface of the modulator in lines, oriented in a direction (y) at right angles to a direction (z), and columns at right angles to the lines, oriented in a spatial direction (s) contained in the plane (xz) formed by the direction (z) and the direction (x), the direction (x) being at right angles to the direction (y) and to the direction (z), - a control means for programming the phase shifts of the pixels of said spatial phase modulator; - a telescope (1, 2) for enlaring said input pulsed beam, arranged between the input and the spatial phase modulator, making it possible to adjust the size of the input pulsed laser beam to that of the spatial phase modulator and forming an incident beam oriented in a direction of incidence contained in a plane at right angles to the direction (y) of the lines; - a spatial filtering means for the light beam diffracted by the spatial phase modulator that is propagated in the direction (z); the phase shifts of the pixels of the spatial phase modulator being programmed, in such a way as to emulate an echelle diffraction grating (3, 3') made up of individual facets; the individual facets being arranged in the direction (y) of the lines, and the angles formed, in the plane (xz), by the individual facets with the spatial direction (s), known as the individual facet angles, being varied along the spatial direction (s). - an input for allowing an input pulsed laser beam to enter; - a spatial phase modulator, arranged on the path of said input pulsed laser beam to be illuminated thereby, and consisting of pixels arranged on a surface of the modulator, each programmable separately to introduce a phase shift of between 0 and 2π, organised on the surface of the modulator in lines, oriented in a direction (y) at right angles to a direction (z), and columns at right angles to the lines, oriented in a spatial direction (s) contained in the plane (xz) formed by the direction (z) and the direction (x), the direction (x) being at right angles to the direction (y) and to the direction (z), - a control means for programming the phase shifts of the pixels of said spatial phase modulator; - a telescope (1, 2) for enlaring said input pulsed beam, arranged between the input and the spatial phase modulator, making it possible to adjust the size of the input pulsed laser beam to that of the spatial phase modulator and forming an incident beam oriented in a direction of incidence contained in a plane at right angles to the direction (y) of the lines; - a spatial filtering means for the light beam diffracted by the spatial phase modulator that is propagated in the direction (z); the phase shifts of the pixels of the spatial phase modulator being programmed, in such a way as to emulate an echelle diffraction grating (3, 3') made up of individual facets; the individual facets being arranged in the direction (y) of the lines, and the angles formed, in the plane (xz), by the individual facets with the spatial direction (s), known as the individual facet angles, being varied along the spatial direction (s).