Fig. 1. Experimental layout showing the division of single material target split into Layers A and B and the location of the front and rear spectrometers.

Fig. 2. Spectral transmission PB(λ) calculated for different temperatures and constant plasma layer thickness of dB=10  μm.

Fig. 3. X-ray spectra measured from the rear sides of Si foil targets with different thicknesses (black thin lines) and best fit modeled (thick purple lines) for temperatures Te,B from 140 to 330 eV and absorbing plasma layer thickness dB=5  μm. Spectral calculations at temperatures that differ from the best-fit value are shown by the thin blue lines and indicate the uncertainty in the current method.