Band-selective Measurement of Electronic Dynamics in VO2 using   Femtosecond Near Edge X-ray Absorption
  We report on the first demonstration of femtosecond xray absorption spectroscopy. Our experiments are made possible by the use of broadly tunable bending-magnet radiation from laser-sliced electron bunches within a synchrotron storage ring. We measure ultrafast electronic dynamics associated with the photo-induced insulator-metal phase transition in VO2. Symmetry and element specific xray absorption from near 500 eV V2p and O1s core levels separately measures the filling dynamics of differently hybridized V3d O2p electronic bands near the Fermi level. 
A.Cavalleri, M. Rini, H.H.W. Chong, S. Fourmaux, T.E. Glover, P.A.   Heimann, J.C. Kieffer, R.W. Schoenlein