Figure 2
Energy spectra of laser-accelerated protons. The energy spectra measured using integration-type ion detector unit with the CR-39 plate at nozzle temperatures of 25 K (red solid line) and 50 K (blue broken line). The energy spectrum measured with the stack of nuclear emulsion films at the nozzle temperature of 25 K (green dotted line) is also shown as reference data50. The error bars on the ordinates represent the standard deviations of the number of the etch pit/track counts accumulated for over 70 laser shots, while those on the abscissa represent the measured energy range. These detector units were installed at a distance of 1.8 m from the laser focal point along the laser propagation direction.
