Tham khảo tài liệu 'advances in solid-state lasers: development and applicationsduration and in the end limits part 16', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 592 Advances in Solid-State Lasers Development and Applications energy a proton can gain is also determined by its radial distance from the laser spot. Protons located in the centre of the field are accelerated the most up to the maximum energy l Vmcix whereas protons outside experience a lower electric field strength and consequently are accelerated to lower energies. As a consequence of both the screening effect and the transverse inhomogeneity of the electric field the resulting spectrum has a strong correlation to the initial distribution of the protons to be accelerated from the target. Following this understanding Esirkepov and Bulanov proposed an acceleration scheme for the generation of monoenergetic beams where all protons are radially confined to a dot source within the central homogeneous region of the TNSA field Esirkepov et al. 2002 . If the proton source is furthermore sufficiently thin so that screening effects are negligible all protons experience the same potential and are accelerated to a monoenergetic distribution. This is depicted in Figure 14 a . Similar to standard TNSA an intense laser pulse impinges onto a thin target foil and generates a sheath of hot electrons at the target back side. But now there is a dot instead of transversely extended layers constituting a thin radially confined ion source being located in the central homogeneous field region. Recent theoretical studies Robinson Gibbon 2007 showed that the limitation of the source thickness is actually not a critical criterion but that for thicker dots the formation of monoenergetic spectra is supported by charge separation effects between two ion species with different charge to mass ratio q m . protons and carbon cf. Fig. 14 b - d . Robinson Gibbon showed in a detailed study regarding micro-dot acceleration that monoenergetic spectra can in fact be produced from dots of up to micrometer thickness and may even vanish if the source layer is chosen too thin. So how does the charge .
