Production of multi-MeV Bremsstrahlung x-ray sources by peta-watt laser pulses on various targets

During the interaction of a high-intensity picosecond laser pulse with a plasma, a large amount of relativistic electrons are accelerated. If these electrons interact with a high-Z solid target, Bremsstrahlung photons are generated. This multi-MeV x-ray source may be used in various applications including radiography and photonuclear studies. The characteristics of such sources, produced with a peta-watt laser interacting with different targets, are investigated numerically, using laser-plasma interaction and transport codes to model the relativistic electron acceleration and their transport in the conversion target, respectively. If the laser pulse interacts with a pre-plasma in front of a solid target, the on-axis dose first increases with pre-plasma scale-length, but then saturates and fluctuates, due to strong filamentation of the peta-watt pulse. In an ionized gas jet, laser hosing reduces the electron emission along the propagation direction and thus the dose. For a capillary tube filled with plasma, the laser pulse is well confined along the axis and a net increase of the on-axis dose is obtained. The X-spot size obtained for these different cases varies from 20 pm to a few hundred microns. (authors)