Undoubtedly, the acceleration of charged particles has been one of the most active research fields in the physics of laser-matter interaction all along the last ten years. In itself, laser driven ion acceleration was already a well known phenomenon although essentially circumscribed to the thermal expansion of the coronal plasma typical of nano and sub-nanosecond low intensities laser pulses interaction regimes.
Thanks to the CPA technique, introduced in the ending 80' it has been possible to dispose of short, more and more intense laser beams. From that time on, intensities ≥ 1018W/cm2 have been available allowing to explore laser-matter interaction in the so-called "relativistic domain" as the motion of electrons in such an electromagnetic field is indeed relativistic. The huge electric fields produced in plasmas due to the laser-induced charge separation open new fields of research in the domain of charged particle acceleration. The admitted scenario for proton acceleration, called Target Normal Sheath Acceleration (TNSA), involves three consecutive steps. First, the laser pre-pulse creates a thin plasma layer at the surface of the foil.
Then, the intense part of the pulse interacting with this thin layer accelerates electrons toward the foil. Finally, the electron beam reaches the rear surface and creates a strong electrostatic field which first ionizes and then accelerates protons and ions to high energies. The excellent emission properties these ion beams show make them particularly suitable for a wide number of applications including high resolution probing of electric fields in plasmas, fast ignition applications, induction of nuclear phenomena, isotope production for medical applications, and proton therapy.