High charge ion beams with achromatic divergence by the BELLA petawatt laser*

 We report on an experimental study of ion acceleration from micrometer thick metallic targets using the BELLA petawatt laser. Here, we show that for the first time, high quality ion beams can be generated under 0.5 Hz high repetition rate with a petawatt laser system, delivering unprecedented single shot doses up few 1000s Gy. By using a large focal spot size (r0=53 um), proton beams with a significant reduced divergence (<250 mrad) are observed. In addition, the proton beams present a remarkable thickness-dependent achromatic feature in high energy range, for example, in case of 2 um Ti target, the proton beams present constant divergence angle of ~100 mrad beyond 3.2 MeV. Such ion beams are of particularly interest for applications that require high ion charge density.