Inelastic light scattering from a Mott insulator
  We propose to use Bragg spectroscopy to measure the excitation spectrum of the Mott insulator state of an atomic Bose gas in an optical lattice. We calculate the structure factor of the Mott insulator taking into account both the selfenergy corrections of the atoms and the corresponding dressing of the atom-photon interaction. We determine the scattering rate of photons in the stimulated Raman transition and show that by measuring this scattering rate in an experiment, in particular the excitation gap of the Mott insulator can be determined. 
D. Van Oosten, D. B. M. Dickerscheid, P. van der Straten, and H. T. C.   Stoof