[en] The experiments in which matter is compressed through power laser requires probe techniques able to measure the atomic structure in very short times. An X-ray diffractometer has been specially designed for the LULI2000 laser. One of the two laser beams is used to compress matter while the other one is used to generate X-rays. The main challenge lays in the ability of the diffractometer to tell the diffracted signal given by the compressed material from the intense background noise. A shielded box surrounding the sample to be compressed has been designed. 5 inside sides of the box are covered with X-ray detectors and on one side an aperture allows X-rays to irradiate the front side of the sample while the back side of the sample is compressed by the laser radiation. Combined with a pressure probe, this device has allowed the study of the evolution of the atomic structure of an iron sample beyond 200 GPa pressure. (A.C.)