Laser Acceleration of Highly Energetic Carbon Ions Using a Double-Layer Target Composed of Slightly Underdense Plasma and Ultrathin Foil

We report the experimental generation of highly energetic carbon ions up to 48 MeV per nucleon by shooting double-layer targets composed of well-controlled slightly underdense plasma and ultrathin foils with ultraintense femtosecond laser pulses. Particle-in-cell simulations reveal that carbon ions are ejected from the ultrathin foils due to radiation pressure and then accelerated in an enhanced sheath field established by the superponderomotive electron flow. Such a cascaded acceleration is especially suited for heavy ion acceleration with femtosecond laser pulses. The breakthrough of heavy ion energy up to many tens of $\mathrm{MeV}/\mathrm{u}$ at a high repetition rate would be able to trigger significant advances in nuclear physics, high energy density physics, and medical physics.

Figure 1

(a) Schematic drawing of the cascaded acceleration process. (b),(c) Raw data and ion spectra obtained from a 20-nm DLC target [upper image in (b), red lines in (c)] and a double-layer target with $80\mu \mathrm{m}$ CNF [lower image in (b), black lines in (c)]. The dashed lines in (c) show the detection threshold. (d) The dependence of the maximum proton or carbon energy on the thickness of the CNF layer.

Figure 2

(a) Snapshots of transverse electric field ($E_y$), longitudinal electric field ($E_x$), and the energy density [$(\gamma -1)n_e$] of electrons from CNF at different times. (b) Snapshots of the density of ${\mathrm{C}}^{6+}$. (c) Energy spectra of electrons in CNF (red line) and in DLC (black line) at $T=480\mathrm{fs}$, and the ${\mathrm{C}}^{6+}$ spectra at different times.

Figure 3

(a) Energy gain rate ($\mathrm{MeV}/\mathrm{fs}$) of ${\mathrm{C}}^{6+}$ ions as a function of time for targets with different CNF layers obtained from simulations. The arrows show the arrival instant of the laser pulses for different cases. (b) The dependence of maximum ${\mathrm{C}}^{6+}$ energy on the thickness of DLC for single DLC targets and double-layer targets obtained from simulations.

Figure 4

Summary of reported experimental results (shown by the reference number) and scaling of carbon ions in cascaded acceleration scheme.