Schematic of the experimental setup for 45°. For normal incidence, the electron spectrometer, transmission screen, and Thomson Parabola were relocated to be at target normal.
(a) Normalized fast diode traces of laser energy contrast vs. time. The precompressor laser pulse representing the XPW case (red) and the post-DPM pulse (green) are taken simultaneously. The ASE pedestal is clearly observed before the DPM, it appears as a ramp due to the integrating nature of the photodiode. (b) Full power energy flux measurements (squares) of the laser before the main pulse arrive from 3rd order autocorrelation traces with a laser power of 30 TW. The inferred DPM contrast is shown, along with the plasma formation threshold. Lines shown for visual aid only, and do not correspond to the actual prepulse structure.
(a) CCD image of the focal spot with calibrated position. (b) Lineout of the focal spot (solid blue) with the lineout of an Airy Disk (dashed green).
(a) Proton spectra with 30 TW on target and dual plasma mirrors for a SiN target (blue triangles) and XPW pulse cleaning with a SiN target (red squares). The noise level is indicated with the dashed line. Also shown are the corresponding raw Thomson parabola ion spectrometer traces for (b) XPW and (c) for dual plasma mirrors.
Thomson Parabola trace for (a) SiN target and (b) Teflon target. Selected ions are identified. Some ions overlap due to identical charge to mass ratios.
(a) Proton energy v. divergence half-angle for 0.03 (red squares), 0.1 (blue circles), and (green triangles) targets. The error is 2°. (b) Target thickness v. average angle of the peak proton signal, relative to target normal. Targets and above showed no deflection from target normal. (c) Schematic of the filter stack for the divergence measurements. A pinhole in the center of the filter stack and CR-39 allowed signal to reach the ion spectrometer.
Maximum proton energies (blue diamonds) and ions (red triangles) versus target thickness for all targets at normal incidence with dual plasma mirrors averaged over many shots. The protons show an exponential increase in energy with decreasing thickness, while the carbon ions show a rapid rise in maximum energy per nucleon as target thickness drops. Carbon data are shown for thicknesses where the fully ionized carbon is the dominant charge state.
Initial 1D density profiles along the laser propagation direction for the (a) XPW and the (b) DPM case. In the XPW case, the regions where protons are present are highlighted in the green patterned regions. In the DPM case, the protons lie along the dashed lines. (c) Comparison of the proton energy spectra for the two cases for 350 nm SiN targets. (d) Comparison of the proton spectra generated with the OSIRIS code (blue) compared to an implicit PIC code developed at NRL (green squares) with identical parameters.
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