My work deals with the theoretical and numerical study of kinetic and relativist plasma. I am developing and using the Particle-In-Cell (PIC) code CALDER. I mainly study the modeling and understanding of the interaction between an ultra intense laser with a target and the subsequent production of ultra fast and intense particle and radiation sources. Different topics investigated are: the laser wakefield acceleration; ion acceleration from solid target; emission of various X and Ɣ rays (such as betatron sources in a wakefield accelerator, Kα and Bremsstrahlung photon emission from a solid target, etc.) or photons with lower frequencies (THz sources). I also investigate the physics of electrons beam propagation in plasma and the effects of strong field QED (e.g. efficient generation Ɣ photons and positrons) which arise when the laser or particle beam used are characterized by extreme properties.