Generation of 0.5GEV C6+ ions from irradiation of ultra-thin foils with high contrast, high intensity laser pulses

Summary form only given. Laser-driven particle acceleration has been under intense investigation for the last decade and is of particular interest for key applications such as medical physics, fast ignition and inertial confinement fusion. The dominant ion acceleration mechanism is known as target normal sheath acceleration (TNSA); although easy accessible it suffers from a low energy conversion efficiency. Recently reported maximum ion energies are in the range of a few tens of MeV, which is well below the energies needed for most applications. Recently proposed acceleration mechanisms utilize ultra-high contrast laser pulses and ultra-thin solid targets allowing for generation of ions in the GeV range from intense laser-plasma interaction. A high laser contrast suppresses pre-ionization of the solid target by any pre-pulses or laser pedestals and in theory enables acceleration beyond TNSA in regimes such as the break-out afterburner (BOA)² or radiation pressure acceleration (RPA). In the light of these novel acceleration regimes we report on the generation of 0.5GeV C6+ carbon ions from interaction of high intensity (10²⁰ W cm^-2) and high contrast (10¹⁰) laser pulses with solid targets. We used free-standing ultra-thin diamond like carbon foils (DLC) in the range from 3 nm to 50 nm, which were produced at our target fabrication laboratory. The high SP3 content of about 75% yields an increased laser damage threshold and greatly supports suppression of target pre-ionization. With the production of GeV scaled ion energies we increased the maximum energy by one order of magnitude and for the first time demonstrated an acceleration beyond TNSA. This represents a significant advance towards compact and feasible ion sources for a large variety of applications, especially in medical phyiscs.