Fig. 2: Transition from RSA to SA.
From: Transient absorption of warm dense matter created by an X-ray free-electron laser
a, Transmission of an XFEL pulse centred at the L2 and L3 edges of a 100-nm-thick Cu foil as a function of pulse intensity I. In both cases, the transmission first decreases (RSA), reaches a minimum and then increases (SA) as a function of intensity. b,c, Transmission at the L3 edge (b) and L2 edge (c) in selected spectral regions below the L3 or L2 pre-edge (1,4), on the L3 or L2 pre-edge (2, 5) and on the L3 or L2 edge (3, 6), respectively, as shown in corresponding panels d and e. d,e, The solid lines show the cold reference spectra (absorption coefficient μA) whereas the dotted lines show spectra where the pre-edge features are prominent, as obtained at I = 5 × 1013 W cm−2 (d) and I = 9 × 1014 W cm−2 (e). The vertical dashed lines, labelled 3dN, show the calculated 2p3/23dN → 3dN+1 excitation energies of various ions (Supplementary Information Section VI.B). The error bars in a, b and c indicate the 95% confidence intervals.
