The invention relates to a system with a multi-jet gas nozzle for experiments with laser radiation, intended for generation of laser radiation harmonics, in case of broad-band laser beams, using multiple gas jets, with submillimetric distances between the jets, thereby permitting the control of gas density distribution modulation period. According to the invention, the system comprises a positioning system having up to six degrees of freedom, in order to finely variate the relative position of a gas-injection nozzle in relation with a laser beam, along the two axes of the space, x and y, which are perpendicular to the beam propagation direction, z, while permitting the nozzle to rotate about axes parallel to x and y, the nozzle having some slots arranged under variable angles in relation with the laser beam propagation direction, z.