2013, Steinke, S., Hilz, P., Schnürer, M., Priebe, G., Bränzel, J., Abicht, F., Kiefer, D., Kreuzer, C., Ostermayr, T., Schreiber, J., Andreev, A.A., Yu, T.P., Pukhov, A., Sandner, W.

We present experimental results on ion acceleration with circularly polarized, ultrahigh contrast laser pulses focused to peak intensities of 5×1019 W cm-2 onto polymer targets of a few 10 nanometer thickness. We observed spatially and energetically separated protons and carbon ions that accumulate to pronounced peaks around 2 MeV containing as much as 6.5% of the laser energy. Based on particle-in-cell simulation, we illustrate that an early separation of heavier carbon ions and lighter protons creates a stable interface that is maintained beyond the end of the radiation pressure dominated acceleration process.