Heating of thin foils with a relativistic-intensity short-pulse laser

K-shell x-ray spectroscopy of sub-100 nm Al foils irradiated by high contrast, spatially uniform, 150 fs, Ilambda(2)=2x10(18) W mum(2)/cm(2), laser pulses is obtained with 500 fs time resolution. Two distinct phases occur: At less than or equal to500 fs a broad feature comparable to the resonance transitions occurs due to satellites, and at greater than or equal to500 fs the resonance transitions dominate. Initial satellites arise from a large area, high density, low temperature (similar to100 eV) plasma created by fast electrons. Thus, contrary to predictions, a short, high intensity laser incident on a thin foil does not create a uniform, hot dense plasma.