High-Resolution XUV Absorption Spectra of Radiatively Heated CH Foils

We have performed measurements of the absorption spectra of X-ray heated thin (1 mum) CH foils in the spectral region of the carbon K-edge (200-500 eV). One arm of the Nova laser is incident on a 025 mum thick Au foil, producing a soft X-ray source that radiatively heats the CH sample, placed in close proximity to the foil. Absorption spectra are obtained by viewing the soft X-rays from the Au foil, passing through the sample, with a 3 m grazing-incidence spectrometer. We observe strong absorption from bound-bound transitions, in qualitative agreement with calculations (OPAL). These measurements resolve questions raised in earlier work (EDWARDS J. et al., Europhys. Lett., 11 (1990) 631) where thicker samples (5 mum) led to absorption saturation and the formation of an <> structure near the position of the cold-carbon edge.