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(Color online) (Left) Experimental setup. (Top right) Images of the focal spot on target measured at full laser energy with (right) and without (left) two plasma mirrors before focus. The grey scale is relative to the peak intensity for both images. (Bottom right) RCF layers within the stack showing the proton beam accelerated from a thick SiN target with proton energies as indicated. The grey scale levels correspond to the dose in units of Gy.
(Color online) Angularly integrated experimental proton energy spectra inferred from RCF for various target thicknesses and a duration, energy, and intensity laser pulse, and the spectrum obtained from the two-dimensional PIC simulations. The films in the stack are of HD-810 type from ISP Corp. Each data point corresponds to a film in the stack. Horizontal error bars correspond to the energy range measured by a particular film and the vertical error bar represent the uncertainty in the calibration of the detector that induces uncertainties in the absolute proton number.
(Color online) (a) Electron energy distributions in the simulation box after the peak of the pulse has reached the target for a target with no collisions (solid), an target with collisions (dashed) a conventional target with collisions (dot-dashed). The spectra are obtained by integrating the energy distribution in the whole simulation box. Inset: Electron momentum before the peak of the pulse reaches the target for an target with no collisions (dark/red), and a conventional target with collisions (grey/green). (b) Density profile measured on the laser axis in the simulation box at the same time than (a). Dashed: density measured for the target, solid: density measured for the target without collisions.
2D spatial distribution of the electron energy density before the peak of the pulse reaches the target for a conventional target with collisions (left) and an ultrathin target with no collisions (right).
(Color online) Results from 2D PIC simulations: (left, circles) maximum proton energy, and (right, triangles) absorption of the laser pulse in the case of the interaction of laser pulses of various intensities with ultrathin targets with thicknesses as indicated. The thickness of the target is varied according to the laser intensity in order to maintain an optimal absorption (Ref. 3).
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