Optimization and Control of Laser-Accelerated Proton Beams

The irradiation of thin metal foils by high-energy short-pulse lasers with intensities above 10^18 W/cm^2 leads to the acceleration of mega-electron-volt (MeV) ion beams. Until today, though, there is no complete model for the laser ion-acceleration that can be used for the determination of all ion beam parameters. However, the development of applications requires an accurate knowledge of the space and momentum distribution of the ions. Therefore the measurement technique of “Radiochromic film Imaging Spectroscopy (RIS)” has been developed and used in experiments at various laser systems world wide. The results obtained with RIS have been considered in a 3D particle tracking code that can fully reproduce the measured data. Further experiments were performed to demonstrate beam manipulation either by different target geometries or laser beam shapes. In order to control the intrinsic beam divergence, miniature quadrupole-lenses have been utilized to demonstrate the first controlled transport and focusing of laser-accelerated MeV-protons. 10^6 protons with an energy of 14 MeV could be reproducibly focused to a small beam spot in a distance of 50 cm from the source.