Generation of High Quality Laser Accelerated Ion Beams
  In order to achieve a high quality, i. e. monoergetic, intense ion beam, we propose the use of a double layer target. The first layer, at the target front, consists of high-Z atoms, while the second (rear) layer is a thin coating of low-Z atoms. The high quality proton beams from the double layer target, irradiated by an ultra-intense laser pulse, are demonstrated with three dimensional Particle-in-Cell simulations. 
T. Zh. Esirkepov, S.V. Bulanov, K. Nishihara, T. Tajima, F. Pegoraro,   V. S. Khoroshkov, K. Mima, H. Daido, Y. Kato, Y. Kit...