Fig. 2

Spectral charge (a) and spectral divergence (b) on a single calibration shot, reconstructed from a stack of 25 HD810 radiochromic films. Circular dots on panel (a) indicate the Bragg peak energy within each foil on the stack. Foils #1 through #4 are saturated; foils #20 through #25 were not exploitable for the fitting procedure and only used to assess the cut-off energy.