Laser-acceleration of high energy protons. Study of acceleration mechanisms and beam handling

In the last few years, intense research has been conducted on laser-accelerated ion sources and their applications. These sources have exceptional properties, i.e. high brightness and high spectral cut-off, high directionality and laminarity, short burst duration. We have shown that for proton energies >10 MeV, the transverse and longitudinal emittance are respectively <0.004 mm-mrad and <10-4 eV-s, i.e. at least 100-fold and may be as much as 104-fold better than conventional accelerators beams. Thanks to these properties, these sources allow for example point-projection radiography with unprecedented resolution. They also open new opportunities for ion beam generation and control and could stimulate development of compact ion accelerators for many applications. Energy increase and beam handling are now major challenges that these ion source face. We have been studying scaling laws for the maximum energy of laser-accelerated protons. This has allowed us to show that there is an optimum in the laser pulse duration of ∼200 fs-1 ps, with a needed laser energy level of 30 to 100 J, in order to achieve e.g. 200 MeV energy protons. We have also performed first experiments exploring the interaction of ultra-high contrast laser pulses with ultra-thin targets (10s of nm thick) and observed a significant energy increase of the ions in this regime as compared to using thicker foils (>a few μm thick) interacting with a laser having standard ASE. Finally, as for such applications beam control is an essential requirement, we have developed an ultra-fast laser-triggered micro-lens that allows tuneable control of the beam divergence as well as energy selection. (author)